Index of Refraction

Surprisingly, This Is Useful

2012-01-30T17:07:00.001-05:00

On The Road Again

2012-01-30T13:34:00.002-05:00

We're back in the swing, and swing is a very appropriate term for our current chapter - vibrations and waves. B, C and E Blocks discussed the characteristics of simple harmonic motion and examined how mass-spring and pendulum systems demonstrate this pretty well. Make sure you can describe what is happening to kinetic energy, potential energy, restoring force, acceleration, velocity and displacement during an oscillation cycle for both of those systems. We took time to show how Hooke's Law satisfies the relationship that restoring force is proportional to displacement for spring systems and for B and C Blocks, harkened back to our lab on conservation of energy for simple harmonic motion to further nail down these ideas. Tomorrow, B and C begin looking a other physical descriptors of simple harmonic motion such as period and frequency and how they can be measured/calculated. E Block will start on their Pendulum Periods lab...

...which is what F Block worked on today. The period of an oscillation is the amount of time required to make one full trip back to the start (crossing equilibrium twice). Period is measured in seconds and we'll look more closely at its relationship to frequency (the number of oscillations per second) in a couple of days. Groups tested three physical features of a pendulum that might influence period: mass, amplitude and length. Tomorrow, we'll graph out our data and draw some conclusions. Then its on to looking at other features of pendulum motion that the other sections hit today.

This Is Why We Need Engineers

2012-01-27T11:57:00.001-05:00

Chemistry Cat - You So Funny

2012-01-27T11:54:00.002-05:00

I've Read a Few of These

2012-01-26T16:58:00.000-05:00

Very Little News Today

2012-01-26T16:35:00.002-05:00

...so here's Deadpool with a taco on his head...

The Midterm March

2012-01-25T12:56:00.003-05:00

B and F Blocks had their midterm exams today and, although I will see F Block tomorrow, I won't see B Block until Monday when everyone starts their unit on vibrations and waves. We'll hit the basics first then move into a more detailed study of sound and light. Our lab for our next chapter will focus on the factors affecting the period of oscillation of a pendulum and a fun time will be had by all...

One Set Down

2012-01-24T12:44:00.001-05:00

C and E Blocks had their midterm exams today and B and F Block will endure them tomorrow. Not much else to say for things going on, but to remind B and F folks that I am here before school tomorrow if they have any last-minute questions. Good Luck!

Midterms

2012-01-23T15:49:00.003-05:00

Well,everyone had a day of whatever help they needed for the upcoming midterm exams. C and E are on the chopping block tomorrow and B and F follow on Wednesday. Remember basic test-taking strategies:

Don't come into the test hungry, thirsty or needing a restroom-break. Take care of all of that ahead of time.

Make sure to have all materials with you such as your writing utensil and calculator. A calculator is especially important since the riff-raff ones I have in class may not be the most efficient ones with which to work your problems.

Use basic logic and common sense - if an answer doesn't make sense, it is probably not the right answer. Physics is all about the real world, so use your instincts.

Eliminate options for multiple-choice questions to increase the probability of being right if you have no choice but to guess on an item.

Skip questions you don't know and come back to them later. Another question might jog your memory or give you a hint and wasting time on a question that you're weak on lessens time you have to work on questions you feel confident about.

Read questions carefully - don't read the first few words and assume you know what the rest of the question says.

You have seen all of the information before - think about what concepts the question might target based on the information given before you start to line up formulas.

Bring work with you - if you finish early, you need something to keep you busy so that you don't resort to chatting and wind up in hot water.

Study so you know the information - not so you can figure it out on the test, since that makes you take far longer on the test than you should and for midterm and final exams you should not count on receiving any extra time to finish your test.

Good luck everyone!

Day is Done

2012-01-20T13:56:00.003-05:00

Everyone is finished with the material for Chapter 11, with F Block going over the ideal of entropy in class today. E Block worked on their Boyle's Law lab after doing a run through of the chapters for the midterm exam. B and C Blocks did the same and then began to look over their practice tests for the midterm and ask questions that they had prepared for review. Remember to ask me for any help that you need or extra problems to work on and if there is something that comes up over the weekend, email me. If you need a video made of how to solve a specific problem, email me early so I can have time to get it done and get it posted. Monday after school is teacher meetings, so I won't be available to stay after - put an X through that on your calendar as extra-help time. Have a great weekend!

Too True...

2012-01-19T17:55:00.002-05:00

Facing Midterms

2012-01-19T15:55:00.003-05:00

Today saw the end of the thermodynamics chapter for B, C and E Blocks. On the heels of yesterday's work on heat engines, cyclic thermodynamic processes and the 2^nd Law of Thermodynamics, we took up the topic of entropy. Although we didn't approach it quantitatively, make sure you are clear about what entropy reflects, that entropy increases naturally in systems, how the 2^nd Law of Thermodynamics relates to entropy and why we see a net increase in entropy for all processes, even if entropy is decreasing in some parts of a system. Tomorrow, E Block works on a Boyle's Lab for part of the period and starts reviewing for the remainder. B and C Blocks start on midterm review and may hit that lab later, if the midterm week time schedule permits.

F Block worked on a lab that examined pressure and volume in a sample of gas. We used the gas pressure sensor to monitor changes in pressure as we compressed a gas and used the data to document the particulars of Boyle's Law. I also made folks determine how much work was done in the process using the available P-V diagram (luckily, LoggerPro does integration). Tomorrow, we'll discuss the lab and take a look at entropy. Then its review for you guys too, so come prepared with questions!

Free For Today Only

2012-01-18T16:59:00.002-05:00

HelloFax is letting people send free faxes to their congressional representatives and senators about SOPA and PIPA:

Stop SOPA and PIPA

SOPA for Gamers

2012-01-18T16:13:00.000-05:00

SOPA

2012-01-18T16:10:00.001-05:00

SOPA Blackout

2012-01-18T15:31:00.002-05:00

No class-information post today to show solidarity with folks who think piracy is unethical, but that censoring the internet is a ridiculous and un-American of attacking the problem.

Thermodynamics!

2012-01-17T13:53:00.002-05:00

We are going to whip through this chapter and after today, I think you see why. It is one of the most information-poor chapters in the book and the math is very simple, so it should be a 3-day trip, at best. In truth, thermodynamics is a massive physics/engineering topic, but a lot is beyond our scope, so the material is just a taste of things you'll find in later classes. Make sure to come prepared on Friday and on Monday with questions about the material for the midterm exam and if you need any practice work, ask me for some. But, you may need to give me a day to hunt up something suitable, so do not wait until the last minute...

Today we took a look at what are thermodynamic systems and how work, heat and internal energy are related in those systems. We redefined work to accommodate the properties of gases (W = PΔV) and examined P-V diagrams to evaluate how much work a thermodynamic system was doing. We also discussed the model thermodynamic processes and examples of each and then restated those using the 1^st Law of Thermodynamics (ΔU = Q - W). You'll get to work with both of today's formulas in the homework problems and the questions will let you practice identifying the examples of thermodynamic processes. Tomorrow - heat engines and heat engine efficiency.

My Brain

2012-01-12T08:16:00.002-05:00

I swear this is about how well it works some days...

Goodbye Chapter 9

2012-01-11T12:06:00.003-05:00

Today was our final interaction with the Chapter 9 material and tomorrow will evaluate how much of that interaction was retained. B, E and F Blocks conducted a review of the material, going page by page and idea by idea through heat and temperature. C Block had that review yesterday and worked on their Heat lab activities today. That served as additional review as the ideas of heat of fusion, specific heat, direction of heat flow, the specific heat and latent heat formulas and rates of cooling were all touched upon in the investigations. The write-ups won't be due until we return from the long weekend, but most folks had time in class to get that started while working on the Newton's Law of Cooling activity. Come Tuesday, everyone will be hip deep in Thermodynamics!

Maybe They'll Do Some Guest Instructing

2012-01-11T07:10:00.000-05:00

Heat Transfer

2012-01-10T12:06:00.002-05:00

C Block had their exam review today, which frees up tomorrow for your lab investigations. Those labs will reinforce today's review of chapter topics and give you some additional practice working with the math of the chapter. The write-up won't be due on Thursday, so don't worry about trying to get that finished while preparing for the exam.

B, E and F Blocks concentrated on mechanisms of heat transfer today. After reviewing the latent heat homework, we launched into a discussion of conduction, convection and radiation and described a number of examples of each heat transfer mechanism at work. Make sure you can define each and recognize examples of each for the test. We also looked at conductors and insulators and how they could be used to regulate heat flow into or out of a system. Again, examples were used to highlight this part of the lesson, so be able to explain an example on Thursday's exam. Tomorrow is review, so come with questions that you have about the material.

Heat and More Heat

2012-01-09T15:45:00.003-05:00

B and F Blocks burned through the concept of latent heat after we reviewed specific heat and how to work problems temperature change caused by energy gain and loss. Phase changes involve energy gain and loss, but without any temperature change. The substance's energy change is of the potential flavor, energy stored in the electrostatic bonds between particles, and changes in potential energy don't affect temperature. We contrasted latent heat of fusion and vaporization and explained why latent heat of vaporization will always be in a higher weight class than heat of fusion. Tomorrow we hit the idea of heat transfer before taking Wednesday as our review day for the upcoming exam.

C Block discussed the mechanisms of heat transfer - conduction, convection and radiation - and described examples of each in action. Make sure you can thoroughly discuss each method of heat transfer (when it occurs, does it need matter, is it rapid or slow) and tell what type of heat transfer is being used in specific examples. Tomorrow, we review for the chapter exam and on Wednesday you get to work on a lab that tidies up a lot of our topics on heat and temperature.

E Block conducted three small investigations that allowed folks to explore heat of fusion, heat transfer between objects at different temperatures and how temperature difference impacts the rate of heat flow between objects. You got a lot of practice working with the specific heat formula and added a new bit of math to the mix - the exponential relationship that is Newton's Law of Cooling. I put some hints on the board to use for writing your conclusion and there's plenty of information in the book and notes to flesh out your explanation of your results. We'll discuss the lab in class tomorrow, before reviewing the latent heat homework and embarking on a discussion of methods of heat transfer.

Specific Heat

2012-01-05T16:40:00.002-05:00

B Block took time to define heat and relate temperature change to the direction of the flow of heat energy between objects. Heat will always flow spontaneously from the object at a higher temperature to an object of lower temperature, but we have to do work on the system to move heat up a temperature gradient. Work can also be done on an object to increase its internal energy, which is why when you hit a nail with a hammer, the nail head feels nice and warm. Tomorrow, we jump into the specific heat arena and the video I'll post below will be relevant to tomorrow's homework.

For C, E and F Blocks, specific heat was the topic of the day. Specific heat is the amount of heat energy we must add or remove to change the temperature of 1 kg of a substance by 1^°C. The higher the specific heat, the more energy necessary for a temperature change and the lower the specific heat, the less energy required. We looked at some examples of specific heat values in class and discussed how the specific heat differences between water, land and air contribute to the moderate climate for coastal areas. Our attention then moved to the method of determining specific heat (calorimetry) and how the basic principle behind calorimetry, aka conservation of energy, can be used to solve problems. Remember that the ΔT variable represents the difference between the final and initial temperatures and approach problems so that ΔT stays positive, even if you have to expand it to T₁ = T_f (opposite of our normal pattern. For C and E Blocks, we'll go over your specific heat homework in class before moving onto the concept of latent heat. For F Block, your homework problems are due on Monday, since tomorrow is lab day!

Here is a quick and dirty video for solving a calorimetry-type problem, which requires you determine the final temperature for the system:

The Irony

2012-01-04T18:38:00.002-05:00

Our focus was "heat" on the coldest day of the school year, so far.

C, E and F Blocks reviewed their homework on temperature before defining heat and detailing why it was a different phenomenon than internal energy. We discussed why heat always moves spontaneously down a temperature gradient and described devices that use work to push heat energy up the gradient (air conditioners and refrigerators). The connection between heat, temperature, internal energy and work ended our time, along with an overview of how James Joule pieced together that particular puzzle. Tomorrow, we jump into the concept of specific heat and how to calculate how much heat is gained or lost by an object.

B Block started their period by reviewing yesterday's lab investigations. Mixing warm and cold water produced curved heating/cooling plots that could be explained by Newton's Law of Cooling, which proposes an exponential pattern to heat loss by an object. When the temperature differences are large, the heat transfer is rapid but as the temperatures move closer together, the rate of energy transfer slows until there is zero net transfer of energy when the system reaches thermal equilibrium. We also looked at why our calculated value for the latent heat of fusion for water was higher than expected. The water in our experiment was not pure water (regular tap water) and a portion of the energy transferred by the warm water did not go into the ice. The system was not a closed one, so the surrounding environment accepted some of the warm water's energy and those factors contributed to the inflated values for L_{f, H₂O}. Our attention then turned to the definition of temperature and how temperature relates to an object's internal energy. The three basic temperature scales were reviewed, as were the ideas of thermal equilibrium and thermal expansion. Tomorrow, we discuss the phenomenon of heat and how it integrates with out discussions of temperature and internal energy. At the same time, we'll connect it with work.

Rowling Would Never Approve

2012-01-03T17:23:00.000-05:00

But this would be so cool...

I Miss Buffy...

2012-01-03T17:00:00.003-05:00

We're Back!

2012-01-03T11:52:00.003-05:00

After a nice, long, relaxing break, we are back with our noses to the grindstone.

C, E and F Blocks began their discussion of temperature which, for most everyone, was a nice review to kick off the week. We defined temperature as the average kinetic energy of the particles in a substance and examined how translational, rotational and vibrational kinetic energies all played in a role in an object's temperature. We then turned to how temperature can change through a gain or loss of energy and how the concept of thermal equilibrium fit into this construct. With the example of how a thermometer can assess an object's temperature, we segued into the idea of thermal expansion/contraction and how it made old-timey thermometers work and was still a critical topic for engineers. We ended with an overview of the temperature scales and the promise that tomorrow will center around the idea of heat.

B Block went over their fluid mechanics exams (as did E Block), then moved into two investigations to introduce the ideas of heat, temperature, thermal equilibrium and phase change. Mixing Warm and Cold water showed the heating and cooling curves for equal masses of water combined and how they reached an equilibrium temperature intermediate between the two extremes. The heat gained and lost was calculated (Q = mcΔT) and compared to demonstrate conservation of energy. Well, as well as it could be conserved in an open calorimeter. The Latent Heat of Fusion investigation looked at the amount of heat energy needed to take water through the solid-liquid phase change. We'll hit all of these topics in detail in this chapter, but your work with in chemistry should have you with a leg up on the material. Tomorrow, temperature, thermal equilibrium and thermal expansion...

Sloth Sanctuary

2011-12-29T19:20:00.002-05:00

Everyone knows I support the Child's Play charity, but I do contribute to others as well. If you are looking to do some good and help out a group that gets little notice but does fantastic work, check out the Sloth Sanctuary in Costa Rica. A little bit goes a long way there and if you can skip a couple of lattes one week, you might consider sending them the savings. They are having a year-end drive that ends on Jan. 1 that could use some propping up:

and you can send them some scratch through Razoo (very nice online fundraising service) by clicking on the image. If you're like me and prefer to help out those that a trillion people aren't giving to already, consider the Sloth Sanctuary. You can give anytime by visiting their site and making a direct donation to this great group.

Hope the break is going well - see you soon!

And Off We Go...

2011-12-22T09:42:00.002-05:00

Today was a day of finishing tests and snatching up some bonus points. What I did is put up to 5 points from your bonus work onto your last test and if you got more than 5, I dropped it onto homework. So, happy holidays from me...

When we return, be ready to launch into new material and don't lose sight of the fact that midterms start not long after we get back from break. You have your notes, tests, review sheets, homework, etc., so do not put off studying for that exam, which goes back to Day 1!

Test Day!

2011-12-21T11:09:00.001-05:00

Oh what fun it is... everyone was engaged in their Chapter 9 exams and, hopefully, all loose ends will be securely tied off before we leave tomorrow. When we return, be prepared to hit heat and topics like heat transfer, change of phase, latent heat, specific heat and all sorts of other goodies...

Big Ol' Review Day

2011-12-20T16:20:00.002-05:00

Tomorrow is the Chapter 9 exam for everyone and today was set aside to tie up all loose ends. We walked through the chapter page by page and addressed any issues that folks had with the material. Email me tonight (early!) or stop by tomorrow before school if you have any additional questions. When we return from break, we'll be jumping into the topics of heat and thermodynamics and that should take us right to the midterm exam!

A Bunch of Hot Air

2011-12-19T07:16:00.002-05:00

Everyone was working on gases today, among other things and that wraps up the new information for the chapter and Wednesday's exam. B and E Blocks discussed the ideal gas law and its derivations (Boyle's, Charles's and Gay-Lussac's laws) and the homework problems tonight focus on working with the ideal gas law. I posted one video over the weekend (9.4 #4) and here's another to help you work through some of the ideas:

9E #3

C Block reviewed their gas law homework, then began a practice test that we will use as part of our exam review tomorrow. F Block went over the same homework, but then moved to the buoyant forces lab that allowed them to see the variation in pressure with depth in a column of fluid and work with the pressure-with-depth formula (which was a special case of Bernoulli's equation for static fluids). We'll go over the lab in class tomorrow and walk through the chapter as part of our review for Wednesday's exam.

For all blocks, when we return from break, the topic of interest will be heat, so prepare for a little bit of a gear change...

Yeah!

2011-12-18T15:45:00.002-05:00

Child's Play charity is just poised to break 2 x 10⁶ k! That's 2 million smackeroos for the exponentially challenged. I just put in my contribution of some DS games that were on Boston Children's Hospital wishlist at Amazon. Looks like lots of locals really opened their wallets this year. I looked at the wishlist early in the season and what remains is only a fraction of what was there. Glad to see that local gamers did their part to help with the cause and make some sick kids a little happier this year...

Gas Law Problems

2011-12-18T11:19:00.004-05:00

Here's a worked out example to help with the work we'll go over tomorrow...

9.4 #4

Center of Mass

2011-12-17T09:54:00.002-05:00

When an object's center of mass is positioned beyond the object's base of support, the object will tip. Glad to know people are out there making practical use of this principle for the benefit of mankind...

Problem-Solving Help

2011-12-15T16:36:00.004-05:00

Here are a couple of videos for tonight's homework (for C, E and F at least)

9D #1

9D #2

9.3 #3

Good old' Bernoulli

2011-12-15T14:05:00.001-05:00

Folks were working with Bernoulli's Principle or equation in class. B Block springboarded from their pressure with depth lab into the ideas associated with fluids in motion. We. looked at types of fluid flow, the ideal fluid model and then looked at how conservation of mass in moving fluids is this field by the relationship outlined by the continuity equation. We'll go into conservation if energy in fluid systems tomorrow. with was the ground trod by C, E and F Blocks. Those classes reviewed Bernoulli's Principle and the continuity equation and pressed forward with Bernoulli's equation. Bernoulli's equation is a mathematical statement that energy in a fluid system is conserved. Energy can be bound In kinetic energy, gravitational potential energy and pressure. The energy can be converted from one form to another any number of times and not all forms may be present at different points in the system. We'll review all of this and the associated homework tomorrow, so do your best working with the ideas and formulas. Then, it is on to properties and behaviors of gases.

I Made a Video!

2011-12-14T19:48:00.002-05:00

Finished watching the new Fright Night film (not bad - David Tennant rules, as usual) and tried out a new app on the iPad. Click the Play button to see what I cobbled together in an unedited round for the continuity equation. Maybe I'll try and keep up with doing some videos, especially if they actually let me make the background dark. I hate white backgrounds...

Fluids are Moving and Grooving

2011-12-14T16:19:00.002-05:00

C, E and F Blocks began a discussion on fluids in motion. We took time to contrast laminar and turbulent flow, described the ideal fluid model, discussed conservation of mass (as satisfied by the continuity equation) and dabbled in Bernoulli's Principle. Bernoulli's Principle explains a number of phenomena in real life that we outlined in class and a few more examples will be added tomorrow. Bernoulli also provides us with Bernoulli's equation, which will demonstrate how fluid systems satisfy the Law of Conservation of Energy.

B Block conducted a lab investigation on variations in fluid pressure with depth. The linear relationship derived from the experimental data nicely corroborated the basic pressure with depth formula: P = P_o + ρgh. We took time to examine the parts of that equation as demonstrated in the investigation and will take time tomorrow to see if you were able to successfully transfer that experience into problem-solving techniques for your homework problems. Then, it's onto fluids in motion!

Catching Up

2011-12-13T17:21:00.003-05:00

Me... not you...

With my absence yesterday, today was a day to take up the slack, tie up loose ends and cover some new ground while we were at it. B and E Blocks reviewed and spot-checked understanding for buoyancy and began a walk through the topic of pressure. We took time to define pressure, contrast it from force, discuss Pascal's Principle and its application to hydraulic devices and explain how and why pressure varies with position in a column of fluid. Tomorrow, we'll put the icing on pressure and begin to take a look a fluids in motion. Well, E Block will do this - B Block will be investigating pressure with depth and the absolute pressure formula: P = P_o + ρgh - and using that to further their discussion of fluid pressure.

C and F Blocks tidied up their work with fluid pressure. C Block conducted a lab investigation that verified the linear relationship between pressure and position in a fluid column and saw that the equation of the line for that experiment was simply the formula for absolute pressure that we worked with in class. Some additional pressure-depth practice problems were assigned for practice and all of this will be reviewed tomorrow before we move on to fluids in motion. F Block discussed the idea of pressure with depth and how that could be extended to the effects on living creatures that we observed when they are exposed to significant variations in environmental pressure. Tomorrow, we move from stationary fluids to fluids in motion and see how that motion affects fluid pressure and direction of motion.

Hipsters...

2011-12-13T12:20:00.001-05:00

...they're everywhere...

Friday is Happy Day!

2011-12-09T16:33:00.001-05:00

B block reviewed their rotational dynamics exams and then moved onto their buoyancy homework problems. That took a bit more time than expected and we took the safe course of working on a few more before moving on to new material. On Monday, we'll start off by looking at these additional buoyancy problems before moving onto fluid pressure.

C Block checked over their pressure problems and then took a look of how fluid pressure varied with depth in the fluid column. Atmospheric pressure is highest at ground level since all the layers of the atmosphere pushing down on your head. As you rise, there is less mass, therefore weight on you, so the pressure diminishes. The same is true when you descend in the ocean. And because objects are 3-dimensional, the pressure on the bottom of the object is larger than the pressure on top of the object, ensuring a net upwards force. There is the origin of the fluid's buoyant force... we'll go over your homework problems on Monday and then tackle the topic of fluids in motion.

E Block investigated Archimedes Principle. For a completely submerged object, the buoyant force is basically constant. But, as you progressively submerged the object, the buoyant force increased as the volume of the displaced fluid increased. Have your write-up ready for Monday, as well as your buoyancy problems to review before we move on to fluid pressure.

F Block reviewed their buoyant forces lab and the associated lab questions and then, after reviewing the buoyancy homework, moved onto fluid pressure. Fluids exert pressure on objects in them and on their containers. For a closed system, if additional pressure is added to the system, it is transmitted equally in all directions in the fluid - Pascal's Principle. We discussed how this applied to hydraulic devices and worked a few problems in class with a hydraulics device. You have a few more to work for homework and we'll go over these on Monday before moving on to looking at how fluid pressure varies with position in a fluid column.

Have a great weekend!

Name the Book

2011-12-09T11:09:00.002-05:00

Another +10 geek points if you know the book... Take a further +10 if you've read it...

Now, We're All Soaked

2011-12-08T17:37:00.001-05:00

On top if the torrential rain that started the day, all groups now are working through the fluids unit. B and E Blocks had a discussion about buoyancy and how to experimentally and mathematically determine the magnitude of buoyant forces. Tomorrow, E Block will work in a lab that will let them take a closer look at buoyant forces and preview a few ideas about the effects of depth or altitude on forces and pressure. B block will begin their study of fluid pressure with a look at Pascal's principle and hydraulics.

B Block discussed fluid pressure in class and looked at some techniques for solving problems involving simple hydraulic devices. Tomorrow, we look at how depth or altitude influences the pressures objects experience. E Block worked on their lab on buoyant forces and investigated how sending a object deeper into a fluid affected the size of the upward force acting on the bottom of the object. By graphing the force on the object versus depth, we were able to determine the density of the fluid in which the object was submerged. We'll review this lab tomorrow, go over your homework problems for buoyancy and then move into the arena of fluid pressure.

Facing Fluids

2011-12-07T16:21:00.002-05:00

B and E Blocks worked on their rotational dynamics and equilibrium exams today, while C and F Blocks began their work on fluid mechanics. Liquids and gases have their own characteristic interactions with forces and we started with the idea of buoyant forces. Fluids exert upward-directed forces on objects you place in or on them and the resulting change in the object's motion depends on the net force the object experiences (the difference between its weight and the buoyant force). We looked, experimentally and Archimedes Principle, then took the easier method for determining buoyant force : F_B = ρ_fVg. Remember that volume of the displaced fluid is equal to the object's volume. We'll go over your practice problems tomorrow (B Block) or Friday (F Block) and tomorrow will find F Block conducting a laboratory investigation on Archimedes Principle.

Statisticians... and Scientists

2011-12-06T19:34:00.003-05:00

In Transition

2011-12-06T13:59:00.002-05:00

C and F Blocks endured their rotational dynamics and equilibrium exams today and will jump into the deep pool of forces in fluids tomorrow. B and E Blocks engaged in further review for their exams, which will fall tomorrow. Catch up with me before school if you have any questions.

Conservation of Angular Momentum

2011-12-05T16:22:00.003-05:00

Here's a couple of videos to watch to highlight a few examples of conservation of angular momentum. For the merry-go-round video, pay attention to how much mass is located at the edge of the merry-go-round and what happens to the angular speed when the mass becomes more closely distributed around the axis of rotation. You see the same ideas in the second video, adding in the vector nature of momentum (which we didn't cover in class, but is fun to see anyway).

Rolling to a Stop

2011-12-05T12:03:00.003-05:00

B and E Blocks got a reprieve for tomorrow's exam. We'll have the exam on Wednesday and use tomorrow for general review (E Block) and general review/lever and pulley lab discussion (B Block). For C and F Blocks - the governor did not call. Tomorrow is still the day for your rotational dynamics and equilibrium exam and today was spent reviewing material for that experience. If you need help, email me tonight or stop by my room tomorrow morning before school and we'll see what we can do. On Wednesday you guys move on to forces in fluids, starting with a look at fluid pressure.

Quote of the Day

2011-12-04T13:40:00.001-05:00

"Chickens are too stupid to mutiny."

from MST3K's riff on Prince of Space. Catch the video if you want a laugh...

Friday is Fun Day!

2011-12-02T19:57:00.001-05:00

B Block went over their simple machine homework and then reviewed for Tuesday's exam. On Monday, you'll work on a lab that investigates levers and pulleys that will let you wok with the concepts of mechanical advantage and efficiency. C Block conducted that lab today and found that distance is the key to multiplying your effort force. Apply a force through a large distance and you use a relatively small force to get a job done. F Block conducted only the lever potion o that lab today, but e main concepts were still emphasized (albeit without the fun of working with pulleys and pulley systems). Poo old' E Block spent the period getting some problem-solving practice for Newton's Second Law for rotation, conservation of angular momentum and conservation of energy. I'll get some videos up this weekend to give you some additional guidance, but feel free to email me if you have a question.

See folks Monday!

Simple Machines

2011-12-01T13:44:00.003-05:00

Everyone was in the kingdom of simple machines today. The nature and purpose of machines was discussed, as was the tradeoff between force and distance that is a known consequence of using a machine. The other known cost of using a machine is the loss of useful energy/work, which is assessed by the machine's efficiency. Make sure you can differentiate between ideal mechanical advantage (IMA) and actual mechanical advantage (AMA) and explain why IMA>AMA for real machines. Tomorrow, C Block will work on a lab centered on levers and pulleys and F Block will take on just the lever portion for a short-block activity. B Block will be reviewing for Tuesday's exam, performing the levers and pulleys investigation on Monday, and E Block will get some problem-solving practice for conservation of angular momentum and mechanical energy.

Energy and Machines

2011-11-30T16:35:00.002-05:00

Rotational kinetic energy and conservation of energy was the order of the day for B, C and F Blocks. Rotational kinetic energy is another form of mechanical energy and should rightfully be included when considering conservation of energy. When working problems, remember the tips that we discussed in class and just be very careful and systematic when setting up your equations. Tomorrow, we begin a discussion of simple machines, mechanical advantage and efficiency...

...which was what E Block investigated in lab today. You worked with levers and pulleys, two machines that rely on torque to function, and analyzed how repositioning the effort force for levers and changing number of supporting ropes for pulleys affected mechanical advantage. Effectively, how did changing distance affect the amount of force needed to raise your load or resistance. Machines cannot give us more work out than we put in, but they can increase our effort force or distance. If effort force is increased, the force acts over a small distance. If effort distance is increased, it only generates a small output force. Both factors cannot be multiplied simultaneously. We'll discuss the lab tomorrow and begin our discussion of simple machines, using your results to highlight our talk.

Rotational Analogues

2011-11-29T13:58:00.003-05:00

More of those on deck today for B, C and E Blocks. B Block went over their work on rotational equilibrium, Newton's ^nd Law for rotation and angular momentum. Tomorrow, we'll add on rotational kinetic energy and start our examination of simple machines.

C Block covered the same ground as B Block, but added on rotational kinetic energy, to boot. Rotational kinetic energy is another form of mechanical energy and rotating objects can have plain ol' kinetic energy, rotational kinetic energy or both, depending on the circumstances. Remember to choose shapes wisely for calculating moment of inertia for objects and that v_t and ω can be interchanged using the relationship we learned last chapter:

v_t = rω

Problems often ask you to solve for something like the translational speed of an object after it has rolled down a ramp and you have to use conservation of energy to do so. Rewriting the rotational kinetic energy formula in terms of translational velocity (KE_rot = 1/2 I(v_t²/r²)reduces the number of velocity variables in the problem to one - the one for which you want to solve. You can also rewrite translational kinetic energy in terms of angular speed, if that is the speed you are asked to determine: KE = 1/2 m(rω)²). And, problems can go the other way - giving you a speed, mass and radius and asking how high something would roll up a ramp. You'd have to use that one speed in both kinetic energy formulas so that you could determine the final gravitational potential energy and, therefore height. Tomorrow, we go over these ideas and then move on to simple machines.

E Block got all three new descriptors of rotational motion in one blast and were left having to analyze conservation of angular motion and rotational kinetic energy for a demonstration. We'll go over that tomorrow before you begin your lab work on simple machines.

F Block conducted a lab investigation on torque and rotational equilibrium. As we had discussed in lab, balance (rotational equilibrium) is based on an absence of net torque not an absence of net force and you demonstrated that quite nicely today. You had unequal forces on either side of the meter stick, but by positioning them at the proper locations, you were able to achieve equilibrium. We'll go over the lab tomorrow before moving on to rotational kinetic energy and conservation of energy for rotating systems.

+20 Nerd Points

2011-11-29T10:56:00.002-05:00

if you can ID all the Dr. Who characters in this pic...

Turkey in the Rear-View Mirror

2011-11-28T18:39:00.002-05:00

Back to Work!

B, C and F Blocks reviewed the concepts of torque, center of mass, moment of inertia and rotational equilibrium before moving on to Newton's 2^nd Law for rotational motion and angular momentum. When working with N-2 for rotation, the relationships between the variables are the same as for plain ol' vanilla N-2. Net torque is directly proportional to angular acceleration and inversely proportional to moment of inertia:

τ_net = Iα

For angular momentum, again, the concept is analogous to translational momentum and the formula is a one-for-one substitution when scripting an expression for angular momentum:

L = Iω

And, yes, angular momentum is conserved in the absence of external torque and we discussed the example of the ice skater going into a spin by bringing in their arms to lower their moment of inertia (to raise angular speed) and also collected data using the rotary motion sensor to verify that conservation of angular moment is a valid idea.

E Block discussed the concept of rotational equilibrium. Extended objects can be analyzed in terms of translation and/or rotational equilibrium and we examined some problems that used both conditions of equilibrium to assess the magnitude of forces acting on systems. We'll go over these problems tomorrow before moving on to Newton's 2^nd Law for rotational motion and angular momentum.

Yep...

2011-11-27T10:49:00.002-05:00

And... We're Done

2011-11-23T09:24:00.002-05:00

Well, I am at least. The last two blocks today are my preparation blocks, so I am puttering around the room cleaning up from this week's rotational dynamics labs. B Block finished their data analysis today and we'll discuss what you found on Monday to help you get some ideas for your write-up, although you should already have some idea of what patterns you should be seeing and thinking of reasons why those patterns were wonky, if that happened. C Block discussed rotational equilibrium, which built on the torque and balance lab that we conducted. We looked over a typical problem for rotational equilibrium dealing and students had the chance to practice solving this type of problem. We'll pick up with this when we get back from break.

Facing a Half-Day

2011-11-22T13:44:00.003-05:00

Today was the last full day of the week and it was a busy one...

B Block began their rotational motion lab. Data was collected that allowed students to measure angular acceleration for a variety of torques and that information will be plotted to assess the object's moment of inertia. For the rod with weights, we'll also take a look at how changing the spacing of the weights affects the moment of inertia, though from our previous discussions, you should have a pretty good idea as to the outcome. Tomorrow is set aside for graphing and analyzing your data - don't forget to get the rod data from the other groups!

C Block engaged in a discussion of center of mass and moment on inertia, two very important concepts for rotational motion. An object's center of mass is the point around which the object will naturally rotate when acted on only by gravity. It is also the balance point, and if your center of mass moves beyond your base of support - consider yourself toppled. We'll expand on these ideas tomorrow, along with our lab work on torque and balance.

E Block took a look at torque, center of mass and moment of inertia. Torque and moment of inertia are critical in providing a framework around which to evaluate and explain your experimental results from your rotational dynamics lab, so I hoped good attention was paid by all attendees. Remember that your lab is not due until next Tuesday or Wednesday, so don't kill yourself trying to get it written up over the break. But, do start thinking about how the increasing torques affected angular acceleration for each trial, how increasing mass for your discs affected angular acceleration (when subject to the same torque) and how using a different shape played into the game. For your rod, it approximates point masses acting away from the axis of rotation, so you should have some idea of how its moment of inertia should compare with comparably massed discs. Also, how did changing the mass spacing affect the moment of inertia? Did the pattern make sense? If now, explain what might have happened to give unexpected results.

F Block worked on rotational equilibrium - where objects are subject to a net torque of 0. Whether you are not rotating or rotating at constant angular speed, you are in rotational equilibrium - angular acceleration is noted when you are subject to net torque. Objects can exist in translational or rotational equilibrium, both at the same time or neither, depending on the situation. We looked at some problems to see how to use these two conditions of equilibrium to analyze forces in a system. We'll go over them on Monday when we return and see how folks feel about moving on to angular momentum.

If I don't see you tomorrow - have a great Thanksgiving!

Rotatin'

2011-11-21T13:45:00.002-05:00

B Block took time to focus on the problem solving aspect of rotational equilibrium. Objects can exist in rotational equilibrium, translational equilibrium, neither or both, depending on the specific circumstances. The problems we are looking at have objects in both forms of equilibrium and we are assessing the forces at work. Remember to use both conditions for equilibrium as tools (F_net = 0 and τ_net = 0) and choose rotational axes wisely. A force applied directly to the axis of rotation does not produce torque and that can help reduce the number of variables in a problem. Over the next couple of days, we'll be working on your rotational dynamics lab and I can help you with any individual issues working these problems during lab time.

C Block worked on a lab dealing with torque and balance. When we speak of balance, we are usually talking about an object being in rotational equilibrium and for that to occur, the sum of all torques on the object must be zero. For each mass you placed on your suspended meter stick, you used the weight and lever-arm distance to calculate its individual torque and with a thought about direction, demonstrated that the clockwise torque in your system balanced the counterclockwise torque. The post-lab problems deal with torque and balance and we'll go over those tomorrow before looking at the concepts of center of mass and moment of inertial.

E Block finished the data analysis for their rotational dynamics lab and folks should think carefully about the write-up hints I put on the board. With the disks, how did torque affect angular acceleration and why was the acceleration different between the single disk and the two disks stacked? Why was the slope of the line for your masses on a rod as large a value as it was? Why did the different positions of the masses on the rod affect the slopes of the lines? We'll start going over these ideas in class tomorrow, so pay attention and use those discussions to help script your synopsis.

F Block discussed the idea of center of mass and moment of inertia. We looked at some demonstrations that showed how the ease of rotation was affected by an object's mass distribution and how moment of inertia, torque and angular acceleration played together through the formula τ_net = Iα. We'll delve more deeply into that relationship in the next section when we really focus on the role moment of inertia plays in other aspects of rotational motion.

600!

2011-11-18T15:47:00.002-05:00

This is the 600th Index of Refraction blog post - cool...

B and F Blocks began their work with rotational dynamics with a study of torque. Remember that torque is not a force - it is the ability of a force to produce rotation. We looked at some examples of how lever arm affects what the force accomplishes when applied to a rotating body. And don't forget angle - only the component of the force that is perpendicular to the rotation contributes to torque and the formula:

τ = Fd(sinΘ)

takes those factors into account. We looked at a sample problem where three forces acted on a beam and calculated the torque produced by each force. Forces applied directly on the axis of rotation do not contribute to torque and force that do contribute to torque could produce clockwise (-) or counterclockwise (+) rotation. When calculating τ_net, pay close attention to those signs. On Monday, C Block will work on a lab that centers on torque and rotational equilibrium and F Block will move on to take a look at center of mass and moment of inertia.

Which was what B Block discussed today. An object's center of mass is the point on an extended object where it will naturally rotate around when acted on only by gravity. Toss a baseball bat in the air and it will rotate around its center of mass, but the center of mass itself will trace out the characteristic parabolic trajectory of an object demonstrating projectile motion. However, an object can rotate around any point if you apply a torque and some axes are easier to rotate around than others. That leads to the idea of moment of inertia - the resistance of an object to rotation. If the mass of an object is clustered around the rotational axis, the moment of inertia will be lower than if the mass is spread at a distance from the axis. We looked at a couple of demonstrations to see how mass distribution affects rotation, specifically angular acceleration, and we'll pursue that relationship mathematically in a later section. On Monday, we'll move into the arena of the second condition for equilibrium and see how to analyze objects in translational and rotational equilibrium.

E Block continued their lab work on rotational dynamics. All groups have their data now and will work on data analysis on Monday.

Have a good weekend!

Rotational Dynamics

2011-11-17T18:56:00.001-05:00

C and F Blocks had their graded learning experiences for circular motion today and will move into rotational dynamics tomorrow.

B Block sat down and took a good hard look at the concept of torque, the rotational analogue of force. Torque depends not only on the magnitude of the applied fore, but also the location of the force relative to the axis of rotation. The angle at which the force is applied also matters, as only the force component that is perpendicular to the rotational arm contributes to torque. We looked at a variety of examples that highlighted the role of lever arm and angle on torque and took time to nail down the mathematical finery of the topic. Tomorrow, we'll expand on the contrast between point masses and extended objects by taking on center of mass and rotational equilibrium.

E Block began work on their rotational dynamics lab. Took folks awhile to get comfortable working with the equipment, but all groups were actively collecting angular acceleration data by the period's end. Tomorrow, we will continue to examine the relationship between torque, angular acceleration and moment of inertia. Take time tonight to plan out tomorrow's data collection and, perhaps, doing some reading on moment of inertia.

Turning the Corner

2011-11-16T16:27:00.002-05:00

C and F Blocks put the final nail in the circular motion coffin and will bury it tomorrow with their exam. Then, it's off into other aspects of rotational motion such as torque, moment of inertia, angular momentum...

B Block did some reading and thinking on the subject of torque - the ability of a force to produce rotation. The application of a force is not the final word in the rotation of an object. We have to take into account where the force is applied, which is spelled out in the concept of lever arm. A force applied at a distance from a rotational axis makes for easier rotation than a force applied close to the axis. Think about spinning a bike wheel by putting your hand on the rubber of the tire, or using your finger down near the axle to spin the tire using the spokes. One is easy and one is hard. We'll go into this in detail tomorrow and your lab for this unit will let you quantify this relationship, while dragging in the concept of moment of inertia, to boot. E Block had the day off, so nothing to say about them, but "see you tomorrow" and be ready to work on your rotational dynamics lab investigation.

Still Circiln'

2011-11-15T12:56:00.002-05:00

B and E Blocks took their circular motion exam today and will move on to rotational dynamics tomorrow/Thursday. With the half-day in place, only B Block will meet, but E Block has their marching orders to prepare for Thursday's law on rotational motion.

C and F Blocks did some review work after going over their universal gravitation problems. Tomorrow, F Block will run their centripetal force lab and B will get a bit more review for Thursday's exam.

So...

2011-11-14T20:28:00.001-05:00

If all you're doing is texting - shame on you...

Back in the Saddle

2011-11-14T13:34:00.003-05:00

After a long weekend, we hop right back into circular motion for the final blast before we hit rotational dynamics. B and E Blocks went over their homework for gravitational/centripetal forces and reviewed for tomorrow's exam. No very complex problems, but a lot of little ones to make sure you can work with the skills in the chapter. Still only 25 test items, though, and the short answer should be guaranteed points if you haven't been sleeping in class.

C and F Blocks reviewed their work on centripetal force and took a look at Newton's Law of Universal Gravitation today. Gravity is generated by all mass and the larger the mass, the stronger the gravitational field. As with all fields, as you distance yourself from the mass, the field gets weaker. So, combine those ideas and we get the notion that the force that arises when two gravitational fields overlap is directly proportional to the masses and inversely proportional to the distance between them. Specifically:

F_g = G(m₁m₂)/r²

This is an example of an inverse-square law, and we'll see several of them this year. Tonight's homework will allow you to practice with this formula and remember the head's ups I gave you in class: don't forget "G," don't forget to square/square-root the distance and make sure you can work with your calculator efficiently to punch in all those darned numbers and exponents. Although none of the problems have you work with a distance between two objects and then add the individual radii for your overall calculation, don't lose sight of the fact that the distance is measured between each object's center of gravity which, for a sphere is dead smack in the middle. We'll go over these problems tomorrow and start the review process for Thursday's exam.

Nice Short Week

2011-11-09T17:58:00.003-05:00

We'll pick up education again on Monday, so enjoy your long weekend...

B Block conducted their centripetal force lab, investigating centripetal force, tangential velocity and rotational radius. From our discussion of centripetal force and acceleration, the results should not have been surprising. For a given force, a larger radius requires a larger velocity and as force increases, greater velocity is required to maintain constant radius. On Monday, we'll go over the lab, the homework problems on centripetal force and gravity and review for Tuesday's exam.

C Block worked through tangential velocity and acceleration, with centripetal acceleration and force thrown in for fun. Remember to use the correct units for angular variables and linear variables and that tangential acceleration has a different job than centripetal acceleration. Tangential acceleration reports rate of change of direction, centripetal acceleration reports rate of change of speed. That tangential velocity vector has two components and each acceleration measures rate of change in one of them. It stands to reason, then, that centripetal force produces change of direction of velocity, and you would be right. We'll review these ideas on Monday before starting to work on gravity.

E Block did their own force work today with centripetal force and gravity. Remember that many forces can act as centripetal forces, including gravity, but do not always serve that function in all situations. Work on those homework problems and pay special attention to the gravity piece - that formula gets people into trouble if they forget about the /r² piece.

F Block reviewed tangential velocity/acceleration and centripetal acceleration before moving in to centripetal force. We took time to discuss the basic job of centripetal force and looked at examples of how various forces can take on that role. On Monday, we'll take a special look at gravity - a force produced by all matter.

Tossing in Tangentials

2011-11-08T14:08:00.003-05:00

E and F Blocks added tangential velocity and acceleration to our descriptors of circular motion. Both are instantaneous values with a straight line direction found through drawing the tangent line for the relevant point on the circle. Unlike angular velocity and acceleration, these values are not the same for every point on the object - they vary based on distance from the axis of rotation. The further away from the rotational axis, the larger they are and they decrease in size as we approach the center of the circle. Centripetal acceleration describes the rate of change of direction for the tangential velocity vectors and always points to the center of the circle. Make sure you can use both formulas to calculate centripetal acceleration, based on the velocity value you're given and we'll add in the force that promotes this acceleration tomorrow.

B Block discussed centripetal force in class and related it to our work yesterday on centripetal acceleration. Remember that "centripetal force" is a job description - many forces can serve this purpose and you might have to calculate the value of the centripetal force using Newton's ^nd Law of Motion or assess a normal force before moving on in a problem. We also began our discussion of gravity, which was cut short by the fire drill. Gravity is a force of attraction between all matter and can be calculated using Newton's Law of Universal Gravitation. We'll review this tomorrow very briefly before you start on your lab investigation.

C Block worked on their centripetal force lab, looking at the relationship between centripetal force, radius of rotation and speed of rotation. For your write-up, you only have to include the graphs, data tables and a concluding statement about the relationship between force and velocity versus force and velocity². We'll go over these tomorrow and use the lab to highlight some ideas about centripetal acceleration.

Round and Round We Go

2011-11-07T16:53:00.002-05:00

Everyone was swimming in the rotational motion pool today and we'll keep on with circular motion concepts for one more chapter when this one is done...

C and F Blocks got their introduction to circular motion with a basic description of what circular motion entails and how to measure and describe the motion. Displacement is viewed from the standpoint of how much of the circle covered and is reported as an angle. Remember to have your calculator in radians for this unit, since this is how we will work with angles in this unit. Once displacement has been defined as an angle, the calculation of angular velocity and acceleration follows in the same fashion as for linear motion: ω = ΔΘ/time and α = Δω/time. For kinematics formulas, use the ones you're used to and substitute the angular version of the variable for its linear counterpart. Pay attention in problem solving for how displacement is reported, as there a few ways that it can be presented - 15 radians, 3πradians, 6 revolutions, 4 laps around the track - and you have to make the appropriate conversions for your problem solving. We'll go over the homework problems first thing tomorrow in F Block, then move into tangential (or linear) velocity and acceleration and take a peek at a third acceleration: centripetal acceleration. C Block will be conducting a lab investigation on centripetal acceleration and force that will give folks a look ahead to those topics.

B Block worked through tangential velocity and acceleration, as well as centripetal acceleration. Tangential velocity and acceleration are instantaneous values and exist for every point on the circle. Every part of the rotating object has a set of motion conditions that if there was no centripetal force, would dictate the motion of the object. If you whirl a ball on a string and snip the string, the ball would move in a straight line and speed as indicated by the tangential motion values. Unlike angular velocity and acceleration, tangential values are not the same for every point on the circle - the farther away from the axis of rotation you are, the greater are these values. In fact, it is the differences in the tangential variables that produce constant angular values. Centripetal acceleration is responsible for fiddling with the direction portion of the tangential velocities and is always directed perpendicular to the tangential acceleration and directed towards the center of the rotation. You'll get to play with this acceleration on Wednesday in your lab investigation, but make sure you can calculate it now, either with rotational or tangential velocity as the given velocity value.

E Block began their discussion of rotational motion after an overview of Friday's lab investigation. Objects moving in a circle have the same descriptors of motion as linear motion - displacement, velocity, acceleration, etc. and after a re-imagining of how displacement is reported, the calculation and analysis of angular velocity and acceleration follows easily. Tonight, you are working on angular kinematics - remember to read the problems carefully, use units to identify variables, pay close attention as to who is initial and who is final velocity and be mindful of signs. We'll go over this work tomorrow before adding another type of velocity and two types of acceleration to our descriptors list.

Success

2011-11-05T22:10:00.001-04:00

Is not a vector... never forget that...

That Time of Year

2011-11-04T20:10:00.006-04:00

The Child's Play initiative has officially kicked off for the year! A charity built by the twisted minds behind the Penny Arcade webcomics to support sick children, it gives gamers a chance to show the world that we're not the stereotypical social rejects or violence-crazed nutcases as the media likes to paint us. Donations can be made through PayPal or texting, or you can choose a hospital (I support Children's Hospital in Boston) and click through to their Amazon WishList to buy things to send directly to kids in need. There are a variety of other ways to participate, like donating to Desert Bus for Hope or even creating your own fundraising event like a gaming marathon, so interested folks can find some way to toss their hat into the ring. Times are tough, so it is not easy sometimes to part with any dollars, but if you can do anything, some very sick child would be more grateful than you can imagine. Visit the Child's Play site for more information and try to give a hospital-bound kid a smile...

Chemistry Humor

2011-11-04T19:42:00.001-04:00

Many Happenings

2011-11-04T12:59:00.003-04:00

B Block worked through angular kinematics today, building on last night's reading. After we frame displacement in terms of angles (measured in radians!), calculating angular velocity and acceleration follow the same techniques that we used for linear motion. For the kinematics formulas, they are item-for-item substitutions between the linear variables and their angular counterparts. Same formulas, different motion. We'll review this ground on Monday before tacking on tangential speed and tangential acceleration.

C and F Blocks worked on their test corrections in class due to the time constraints for getting grades submitted. Have them ready for Monday and that will be our official start day for rotational motion.

E Block worked on their centripetal force investigation, looking at the relationship between the magnitude of the force, the rotational radius and the rotational speed. The greater the force, the faster the speed had to be to maintain a constant radius and a smaller radius required less speed to be maintained than a large radius, when the forces were equal. We'll get into deeper discussion of centripetal force and acceleration on Tuesday - Monday is set aside to explore the basics of angular kinematics.

Have a good weekend!

A Lost Day

2011-11-03T17:47:00.002-04:00

I was closeted with a number of my brethren getting training on a piece of software for curriculum mapping (yes, it was as big-sighing as it sounds)so you guys had the run of the day. Well, not quite...

B and E Blocks dipped their toes into rotational motion with basic descriptors of rotational motion such as angular displacement, velocity and acceleration. Once you re-define how we measure displacement for circular motion, the rest just falls into place. B Block will discuss this material tomorrow and E Block will conduct a lab activity on centripetal acceleration and force. Something has to work on changing the direction of the object so that it moves in a circle...

C and F Blocks watched the Mythbusters episode, Ping Pong Rescue, that introduced concepts about buoyancy and forces in fluids. Is this our next chapter? No. But it did let you see how basic observations and experiments work to produce the concepts that we discuss and formulas that we use. Make sure to finish up your discussion questions to go over tomorrow - we will get to forces in fluids in a couple of chapters so your brainwork is not wasted. Tomorrow, owing to the large number of individuals who need to make up the Chapter 6 exam and the looming deadline for submitting Quarter 1 grades, time will be allotted for test corrections and test taking so we can end the quarter with everyone up to date.

See you tomorrow!

Test Day!

2011-11-02T13:24:00.003-04:00

Everyone was engaged with their exams today and tomorrow would have been the official start of circular motion, but I have to spend the day with some curriculum mapping software. Oh, the fun... I can already feel the fun...

Anyway, you'll be busy tomorrow, so don't think it will be a day off. We'll pick up with angular displacement, speed and acceleration on Friday, with E Block working on a lab involving centripetal acceleration and force.

Contact Lenses

2011-11-01T20:23:00.004-04:00

Everyone asks me where I get my contact lenses for my Halloween costume and it is this company:

9mm Special Effects

They provide special effects contact lenses for film, TV and videos - in other words, they know what they're doing to get a good effect that is safe for the wearer. If you ever want to add contact lenses to your Halloween costume, and a number of you say this every year, you HAVE TO shop with a reputable company. Cheap contact lenses can ruin your eyes - you need quality lenses and a good company will accommodate any prescription you might have. Yes, professionally-crafted lenses will cost a bit, but your eyes are worth it...

NPR's 100

2011-11-01T16:42:00.002-04:00

National Public Radio asked listeners to help with a list of the top 100 SciFi/Fantasy books. SF Signal made up a great flow-chart to help you choose something from the list to read. The .jpg is a big image that takes little scrolling to navigate but is a very cool image to work with. If you'd like an interactive version - check out this link: An Interactive Guide to NPR's List of Top 100 Science Fiction and Fantasy books.

Countdown to Test Time

2011-11-01T13:45:00.002-04:00

Today was a day of review for all sections. The review sheet has been up online and folks have hopefully availed themselves of that resource. In class, we walked through the chapter, page by page highlighting relevant material and skills and took time to answer any questions people threw out. On Thursday, I'll be out due to some training they want people to have for some software the district is buying, so our formal start to circular motion work will begin on Friday. Good luck tomorrow!

Happy Halloween!

2011-10-31T13:19:00.002-04:00

Such a busy day of tidying up loose ends for momentum in preparation for our exam on Wednesday. B Block conducted a lab investigation on the impulse-momentum theorem, C and F Blocks discussed elastic collisions and E Block discussed the types of collisions in one whole go. For your collisions, be able to describe their basic properties and what happens in therms of conservation of momentum and kinetic energy. Problem solving involves your basic idea of conservation of momentum, with you having to craft a specific formula work with based on the specifics of the problem. Tomorrow, we'll go over homework, walk through the chapter and get ourselves ready for the exam. On Thursday - circular motion!

Collisions!

2011-10-28T13:52:00.002-04:00

Today was conservation of momentum or collisions, depending on the block. B and F Block worked on collisions with B Block getting perfectly inelastic, inelastic and elastic collisions in one gulp and F Block getting perfectly inelastic collisions in a small nibble. Collisions are categorized by how well they conserve kinetic energy. Elastics do a great job, perfectly inelastics do a poor job and inelastics are in between. Also, for perfectly inelastic collisions, the objects stick together and move as a unit after the interaction. In truth, most collisions are inelastic in nature, but for our purposes, we'll consider them either perfectly inelastic or elastic and go from there.

C Block worked on their Impulse-Momentum lab. Remember to take care in your calculations of momentum change that the signs for initial and final velocity are correct and used properly in the determination of Δp. We'll go over the lab on Monday, but make sure to consider the items I put on the board when framing your conclusion -what should we have seen for the agreement of impulse and momentum change/sources of error in experiment; how did time and magnitude of force compare for the thin and thick rubber band and how does that play into the impulse-momentum theorem.

E Block discussed the idea of conservation of momentum. Although a collision changes the momentum of each object involved, the total momentum of the system remains the same. We have Newton's 3^rd Law of Motion and impulse to thank for this and we examined how momentum conservation played out in different examples from real life. Keep these in mind as you approach problem-solving and setting up proper equations. We'll bring conservation of momentum with us Monday into our discussion of collisions and will see it again when we discuss rotational motion.

Cats is Cats...

2011-10-27T17:25:00.002-04:00

Conservation of Momentum and Collisions

2011-10-27T13:39:00.002-04:00

E Block reviewed yesterday's lab and then moved into a discussion of momentum and impulse, which was the lab's focus topic. Make sure you can explain each of those ideas, as well as implications of the impulse-momentum theorem. We'll go over your homework problems tomorrow, but they should go pretty quickly since you performed the same calculations for your lab analysis.

B and F Blocks had their discussion of conservation of momentum. Remember that conservation of momentum is a system-based concept. It is absolutely expected that the momentum of individual objects changes after a collision. It is the system's total momentum that remains unchanged. A gain by one is matched by an equal loss in the other. We looked at how conservation of momentum arose from Newton's 3^rd Law of Motion and the concept of impulse and how to perform calculations with various conservation of momentum situations. We'll go over those homework items tomorrow before striking out into the different forms of collisions.

C Block spent the period reviewing conservation of momentum and examining perfectly inelastic collisions. For this type of collision, we expect to see a reduction in kinetic energy, although momentum is still conserved system-wide. For these collisions, we assume that the objects stick together and move as a single unit after the interaction and that kinetic energy is lost in the deformation of the objects, as well as though sound and heat due to friction. We'll hit elastic collisions after tomorrow's lab on the impulse-momentum theorem.

For everyone - exam on Wednesday, so start appropriate time and resource management techniques now...

Moving on With Momentum

2011-10-26T13:42:00.003-04:00

B and F Blocks had their introduction to momentum and the impulse-momentum theorem. An object's momentum - the inertia in motion - is affected by the size of the force it experiences and the duration that the force acts on the object. We looked at examples where small forces produced large momentum change (through long time intervals) and where large forces produced small momentum change (through tiny time intervals). Remember that momentum is a vector and inherits the direction piece from velocity. Because of this, it is critical to properly assign and track signs when calculating momentum change.

E Block conducted their impulse-momentum theorem lab, comparing the equivalence of the two for a stiff and loose rubber band. Make careful calculations of momentum change and explain any variations between the measured impulse and the calculated change of momentum. We'll discuss the impulse-momentum theorem tomorrow and use the lab to highlight the discussion.

C Block took a look at conservation of momentum. In a closed system, the total momentum of objects in the system stays the same, regardless of the interactions they experience. However, the momentum of individual objects will change. We looked at how Newton's 3^rd Law of Motion and the idea of impulse mandated conservation of momentum for two objects striking each other (the simplest model) and discussed common scenarios encountered in problem solving. Remember that for systems that start at rest (like a cannonball in a cannon), momentum is still conserved once the cannonball is fired. The cannonball and cannon have equal and opposite changes of momentum, which would still sum to a total momentum of zero. We could use that information, then, to calculate the speed of the cannonball or the recoil velocity of the cannon, if necessary. We'll go over your homework problems tomorrow before taking a closer look at the idea of a "collision."

Videos!

2011-10-25T17:27:00.003-04:00

Some momentum and impulse videos:

Momentum and Impulse

2011-10-25T13:42:00.002-04:00

C and F Blocks started their unit on momentum today. B Block had a discussion focusing on momentum, impulse and the impulse-momentum theorem. Momentum, often viewed as the measure of motion, is the product of mass and velocity. Because of the velocity piece, momentum is a vector with the direction matching the direction of the velocity. This becomes very important when working with momentum change. If directions changes from positive to negative (right to left, north to south), you have to be sure to include the proper signs in your calculations. When an object's momentum does change, we would expect that a force was at the root of it, since the piece of momentum that changed was almost certainly the velocity piece. And, since a change of velocity indicates acceleration, we know a force is promoting the momentum change we measure. But, the duration of the applied force also plays a part and that leads to the concept of impulse.

Impulse is the product of force and time interval. The same impulse can exist for two different forces, if the time interval is also different. A 10 Nxs impulse can be achieved through 5N and 2s, 10N and 1s or 1N and 10s. And all of these will produce the same change in momentum of the object. So, it depends on the situation - do you need a small force or a large force - that will set the time you need to apply the force. We discussed the need for follow-through in sports and the science behind safety devices such as air bags and safety nets and will look more at impulse and momentum in lab, as F Block did today. The lab today used a force sensor to directly measure the impulse acting on a moving cart and a motion detector measured the velocity changes produced by the impulse. Make careful calculations of the change of momentum when working on your lab and think about why it does or does not match the measured impulse and how the loose and tight rubber bands compared in changing the motion of the cart.

B and E Blocks took their work and energy exams and will start on momentum and impulse tomorrow.

The End of Work

2011-10-24T14:15:00.003-04:00

C and F Blocks took their work and energy exams today and will start with momentum and impulse tomorrow. F Block will conduct a lab investigation centering on the impulse-momentum theorem. When we started the previous chapter, we said there were some other things one had to consider about an object's change in motion besides the size of the net force - distance through which the force was acting and the duration of the application of the force. We looked at the distance piece with work and add the time piece in this chapter. The impulse-momentum looks at force, time and momentum change, with impulse being defined as the product of net force and time. In Newton's day, force was looked at as the rate of change of momentum, another way of relating the variables. You'll investigate this tomorrow and C Block will discuss it in class.

B and E blocks reviewed Friday's work on power and also the concepts for the chapter in preparation for tomorrow's exam. As for C and F Blocks, we will move into momentum and impulse after our test and the lab that F Block will conduct on Wednesday will investigate the impulse-momentum theorem.

Work, Power and Energy Videos

2011-10-22T13:12:00.003-04:00

With exams on Monday and Tuesday, here are some videos on the relevant exam topics:

Personal Awareness

2011-10-21T16:32:00.003-04:00

One of my favorite shows ever was Star Trek: Deep Space Nine. I love shows that have a darker theme to them, like this show and Babylon 5. B-5 has been available for streaming for a long time now, but DS9 was just put out recently. Ran across this chart today and had to laugh about what it says about me. (Click through for full sized view).

My absolute, hands-down favorite character was Garak (Mr. Chaotic Neutral). My iPhone is named Garak, to give you an idea of my support... And, let's face it - anyone who has met me can easily picture me saying a line like that. My second favorite character was Gul Dukat (Mr. Chaotic Evil). Not sure what this says about me, but today's Friday so who really cares. But it is an interesting exercise when you're reading a book, watching a movie or following a TV series... who are your favorite characters and what is it about them that generates the interest... what part of you resonates with the characters and what does that say about your personality, strengths and weaknesses, abilities and shortcomings...

Phynally Phryday

2011-10-21T13:48:00.001-04:00

A very long week of work (HAH!) ends with an exam review foe C and F Blocks and a tidying up of conservation of energy and power topics for B and E Blocks. Keep very much in mind at power is a rate function and that it ca be approached from a variety of ways involving work and energy. We'll review these ideas on Monday, in preparation for your exam on Tuesday. I'll take some time this weekend to post some video clips about this chapter's topics, so check in occasionally for that help. Have a good weekend!

Do NOT Do This on the SAT

2011-10-21T12:37:00.003-04:00

Again, Yep

2011-10-21T10:56:00.002-04:00

Ongoing Energy

2011-10-20T16:26:00.002-04:00

Today was B Block's chance to run an investigation on conservation of energy. By observing an oscillating spring and making measurements of the kinetic energy and elastic potential energy, it was clear that the total energy was conserved nicely in this system. Attaching an index card to piece of paper to the bottom of the spring made friction a significant force and conservation of mechanical energy was not observed. Concentrate on your conclusion for your write-up tonight - the patterns of the energy conversions, the adherence to conservation of energy, etc. We'll discuss the lab tomorrow and then wrap up ideas with energy conservation and power.

C and F Blocks discussed the idea of power. The word has its own meaning in daily life and that meaning bears no real resemblance to the scientific use - the rate of energy conversion or the rate at which work is performed. Two machines with different power ratings can absolutely do the same work - the lower-power machine just takes longer. We emphasized that the unit - the Watt - that we see on light bulbs and appliances is the same Watt as for our mechanical energy studies and took some time to observe the power of three computers and a television set. For your poor old parents, remember that electrical power reports the rate of energy consumption by your electronics and every Joule of that energy ends up on the electric bill... tomorrow, we'll go over your power homework problems and review for Monday's exam. Then, it's off to momentum!

E Block strolled through conservation of energy, using their lab focused on energy of a ball thrown into the air as an example. The total energy was nicely conserved in that system, although the energy was continually being converted between gravitational potential and kinetic. When the ball was bounced on the floor, however, conservation of mechanical energy faltered. There was significant loss to non-mechanical forms and the overall energy declined with each bounce. We'll go over your conservation of energy problems tomorrow, then move into power.

Don't Mess With Mendeleev

2011-10-20T16:10:00.002-04:00

Watching the Rise and Fall

2011-10-19T12:04:00.004-04:00

C Block worked on a lab that focused on energy transformations and energy conservation for an oscillating spring. The spring constant was experimentally determined and used for the calculation of elastic potential energy. The object's mass was a known value and the motion detector provided displacement and velocity information for the final energy determinations. The graphs of kinetic energy and elastic potential energy showed nicely the inverse relationship between the two and adding a plot of total energy demonstrated its conservation throughout the oscillations. No matter how often the energy is transformed, the total remains the same. Adding an index card to the bottom of the oscillating mass increased air resistance and the conservation of mechanical energy suffered due to energy transformation to non-mechanical forms. We'll discuss the lab in class tomorrow, go over the conservation of energy homework problems, then launch into a discussion of power.

B and E Blocks finished up our basic mechanical energy forms by adding gravitational potential and elastic potential to the list. Both are energies of position and both represent stored energy. Both are related to the amount of work done on or by the object and both are readily accessible by objects for work. When working problems, make sure to double-check the reference point for measuring height for gravitational potential energy. It isn't always the ground...

F Block took time to review kinetic and potential energies before looking at conservation of energy. Conservation of total energy is a fundamental law of the universe, but conservation of mechanical energy is valid only in low-friction systems. Transformation of mechanical energy to non-mechanical forms or forms useless for motion will reduce the overall mechanical energy the system has available over time. We are going to assume for your homework problems that mechanical energy is well conserved so that ME_i = ME_f. It is up to you, though, to use that relationship to come up with a proper equation to work with this concept in specific situations. We'll go over these problems tomorrow and then take a look at power.

Riding the Energy Train

2011-10-18T18:00:00.003-04:00

Our discussion of work and energy continued today with various people starting at various places. B Block and F Blocks took on the topic of potential energy, with the two examples on stage now being gravitational potential and elastic potential. Easily accessed for work, unlike chemical or nuclear, those forms of potential energy get lumped, along with kinetic energy, as mechanical energy. We looked at both of those energies conceptually and mathematically and will review our work tomorrow before moving on to conservation of energy.

Which was where C Block picked up today. Energy does not care what it is at any time - it readily converts and transforms between forms and types. The only caveat is that the total value is always conserved. Mechanical energy, no so much, due to transformations into unusable, non-mechanical forms, but total energy most certainly is conserved quantity. For mechanical energy, as long as friction and other factors are kept at bay, mechanical energy is conserved well enough to make some good predictions about the behavior of objects. Common problems involve solving for a final velocity for an object falling from a height (with or without an initial velocity)and predicting how high something will rise given a launch velocity. Sometimes the problems would be accessible using kinematics formulas, but they fall down when acceleration is not constant and get complicated when the motion covers two or three dimensions getting to its final location. We'll go over your homework problems tomorrow before moving into power.

E Block began their discussion of work and the work-kinetic energy theorem after a discussion of yesterday's lab. Although we highlight the relationship between work and kinetic energy, a similar relationship exists between work and change of potential energy. We'll dig deeper into potential energy tomorrow, highlighting the one you've worked with in lab, gravitational potential energy and adding a new one, elastic potential energy.

Full of Energy

2011-10-17T13:35:00.003-04:00

B and F Blocks began their study of work and energy today by nailing down the scientific use of the term "work," looking at how the direction of an applied force affects the amount of work it does on an object, examining situations involving positive and negative work and relating work to the kinetic energy change of a object. For F Block, the lab we conducted yesterday helped to highlight the ideas of work and energy. The ball's fluctuations in kinetic energy related to it's speed and represented the work done on it by the person throwing the ball and by gravity while the ball was in free fall. You did positive work on the ball tossing it upwards (sped up), gravity did negative work on the ball on the rise (slowed down) and positive work on the way down (sped up) and you did negative work on the ball when you caught it (brought it to a stop). Tomorrow, we'll add the potential energy piece to the mix.

C Block built on their study of work and kinetic energy by adding in two potential energies we class as mechanical energies - gravitational potential (PE_g) and elastic potential (PE_elastic). Both are readily available for active work, unlike chemical or heat, and are easily convertible to kinetic energy. Both are energies of position - position in earth's gravitational field and final position based on stretch or compression. Changes in position (lifting, dropping, stretching, compressing) represent work being done - these energies represent the stored work that you did. Release that energy and that equivalent of work can now be done by the object. On Wednesday, you'll do a lab that will look at potential energy and it's conversion to kinetic in a dynamic system. That lab will also bring in tomorrow's discussion about conservation of energy.

E Block conducted a lab that looked at energy conversions for a ball tossed in the air. You tracked the changes in kinetic and gravitational potential energy and clearly saw the inverse relationship between the two. The total energy, however, remained constant, demonstrating the conservation of mechanical energy in that low-friction system. That went down the tubes when you allowed the ball to bounce on the floor. Mechanical energy was not conserved as a goodly portion of it was converted to heat, internal energy and sound with each bounce. Total energy in a closed system is always conserved, but mechanical energy declines with time due interactions with other objects in the system. We'll go over the lab tomorrow and refer to it frequently in our discussions of work and energy in this chapter.

Hello Work and Energy!

2011-10-14T13:45:00.002-04:00

B and E Blocks took their forces and laws of motion exam and will get a start on the concepts of work and energy on Monday, with E Block conducting an investigation on conservation of energy. The preliminary questions for the lab that you are working on for homework will introduce you to the relevant ideas for the lab and give you some tools to interpret the results. B Block will engage in a discussion of work and kinetic energy and how they relate through the work-kinetic theorem.

C Block started their work discussion today. The scientific use of the term "work" was highlighted as was the formula we use to calculate work. Remember that the force in the formula is the net force acting on the object and the work assessed will be the next work the object experiences. Positive net force delivers positive work and negative net force delivers negative work. What this can mean is that an object speeds up (+work) or slows down (-work), starts from rest, comes to a stop, or changes direction. But, there must be some displacement for work to be done by that force and, further, the force must have at least some component in the plane of the motion for it to contribute to work. So, for a box sliding across the floor, gravity does no work on the box since the motion is purely horizontal, but weight acts vertically. Because work can produce a change of velocity, it can produce a change in kinetic energy the amount of that change is equal to the work done on or by the object. The work-kinetic energy theorem lets you assess work by measuring velocity changes or use a work value to predict a resulting velocity change for an object. We'll add another energy to our list on Monday, gravitational potential energy and add several more as the year goes on.

F Block conducted an investigation concerning conservation of energy with a ball tossed in the air. You were able to see the patterns of kinetic energy and gravitational potential energy change for the ball in free fall and those changes matched what we would predict based on what we know about free-fall motion. The energy graphs nicely showed that as kinetic energy decreased, gravitational potential increases and vice versa so that the total energy in the system remained constant. For your conclusion section, make sure to include the Extension piece with the bouncing ball (is conservation of energy observed for the bouncing ball - why or why not) and what we would have observed for a high bounce ball in the same situation. On Monday, we will begin our discussion of work and energy and use the lab for that lecture and subsequent ones to illustrate our points.

Have a good weekend!

When You Read....

2011-10-13T16:36:00.001-04:00

Stuff like this makes sense... (hint: pick up a little Arthur Conan Doyle)

One Set of Exams Down

2011-10-13T15:56:00.002-04:00

C and F Blocks had their Forces and Laws of Motion exam today. Some folks need some more time and are filing in tomorrow before school to finish up. In class, C Block will begin their investigation of work and energy with discussion of work. F Block will investigate conservation of energy and conversions between kinetic energy and gravitational potential energy. You're homework tonight is to answer those preliminary questions at the start of the lab and that might involve a perusal of Chapter 5 to nail down the answers. But, it will also get you thinking about the lab concepts and provide a foundation to understand your results. And, I expect you to demonstrate that understanding in the Conclusion section of your lab write-up.

B and E Blocks take their exams tomorrow and if you need more help, see me tomorrow before school. You do have all the skills to work the problems, but you have to be able to decide which skills to use and apply them appropriately. And, don't neglect the basic content and concepts. It is easy to focus only on the math and forget basic definitions and ideas that the math supports. On Monday, we'll begin our study of work and energy with E Block conducting an investigation on energy and energy conservation and B Block diving into the topic of work.

Finishing Forces

2011-10-12T13:40:00.004-04:00

C and F Blocks spent the period tidying up loose ends with friction and air resistance and reviewing for tomorrow's exam. We walked through the chapter page by page highlighting what to pay attention to and highlighted the math skills you will be required to demonstrate. Although there are only two new formula pieces added this chapter - F_net = ma and μ_k,s = F_k,s/F_N - using those formulas is not necessarily straight forward and require careful reading of the problem and drawing accurate force diagrams to puzzle out. Also, be on the look out for the need to perhaps use a kinematics formula to work out acceleration for a calculation of net force. Now, I tried to make this obvious in class, but in case you weren't listening, expect a couple of short answers, one of which is going to be an incline problem. Don't be surprised if you are asked to:

Calculate the weight of an object

Calculate the normal force acting on the object

Calculate the force pulling it down the incline

Calculate the force of static friction holding it stationary on the incline

Calculate the coefficient of friction between the incline and the object

So come ready to tackle that and if you need help, see me before school tomorrow.

B and E Blocks finished up with friction and air resistance in class today. B Block reviewed their homework problems for friction and their Chapter 3 exams and E Block finished their discussion of friction and will go over their friction problems tomorrow. Come with questions as we review for Friday's exam and see me before school if you need any additional help.