Sloth Sanctuary

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...

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!

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

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

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!

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

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

9.4 #4

Center of Mass

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

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

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!

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

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

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...

...they're everywhere...

Friday is Happy Day!

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

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

Now, We're All Soaked

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

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

In Transition

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

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

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

"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!

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

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

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

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

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

Turkey in the Rear-View Mirror

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...

And... We're Done

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

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'

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!

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

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

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'

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...

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

Back in the Saddle

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

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

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

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

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

That Time of Year

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

Many Happenings

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

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!

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

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

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

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!

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!

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...

Conservation of Momentum and Collisions

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

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!

Some momentum and impulse videos:

Momentum and Impulse

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

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

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

Personal Awareness

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

 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

Again, Yep

Ongoing Energy

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

Watching the Rise and Fall

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

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

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!

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....

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

One Set of Exams Down

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

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:

1. Calculate the weight of an object


2. Calculate the normal force acting on the object


3. Calculate the force pulling it down the incline


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


5. 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.

Yep...

Cat's Paw

This is considered the closest thing the original Star Trek has to a Halloween episode... enjoy (even with the stupid commercials)...

Wake Up!

It's school time again, you slackers with your 4-day weekend. Bright-eyed and bushy-tailed we march onwards!

B Block conducted a lab investigation that targeted static and kinetic friction. We measured those values for a block of wood stationary on and moving across your lab table, highlighting the value for F_s,max, the way in which the graphs demonstrated equilibrium and how varying the normal force varied both of these friction measurements. With your data, you will also calculate the coefficient of friction between your surfaces. Remember - mass is not weight, so make sure you are using the object's weight to determine the normal force. Also, when you slid your block across the table and used the motion detector to measure the velocity change, it is important that the data was linear, indicating constant acceleration. Use that acceleration value (the slope of the line you recorded) in Newton's 2^nd Law of Motion formula to determine the value of kinetic friction acting on the block. Tomorrow, we'll go over the lab (though it is not due until Thursday) and the homework on friction before adding air resistance to the mix. Test now scheduled for Friday.

C, E and F Blocks had their discussion of friction and air resistance,though F Block has a tiny piece to catch tomorrow. Objects are subject to friction whenever they contact other matter, whether they are moving or not. Static friction has a larger value than kinetic friction because of the adhesive bonds that are able to form when objects are stationary against each other. Once in motion, the surface imperfections are important aspects of the surface construction to worry about We discussed how the normal force relates to the magnitude of the frictional force and how to work in those pesky surface imperfections in to an equation to evaluate friction. The coefficient of friction can be experimentally determined in lab and used to assess the value of frictional resistance an object experiences. Doesn't mean the normal force still isn't a player, though. A small car and a large truck on the same road do not experience the same force of friction, even if they have identical tires. The trucks larger weight produces a larger normal force and, so, is subject to a larger force of friction. Tomorrow, we'll tidy up loose ends for C and F Blocks, review and launch into Thursday's exam. E Block's exam is on Friday, but we have more ground to cover, so the extra day is needed.

Do Something Good

There are a lot of great charities out there, I'll be plugging Child's Play here soon, for example, and another solid example is DonateGames. They accept donated videogames and consoles and sell them online, with the proceeds benefiting sick kids. Send them pretty much any game or game system and they'll take it, though they also accept good ol' cash via PayPal. Got old games and things hanging around? Consider shipping them out for a good cause. You can also buy used stuff from their site at a nice discount and add to their coffers. They also encourage people to host their own drives to collect games and gaming equipment - might be a nice way for a couple of you guys to accumulate some community service hours and make a real difference in some kid's life. Gamers get such a bad rap in society... it's good to see people shining a good light on the likes of us.

Rolling into the Long Weekend

At least you guys don't have to come in tomorrow - pity the poor teachers who have to sit through meetings and work on curriculum. Yeah, plotting and planning new ways to make you miserable...

B Block got into a deep discussion about friction, both kinetic and static and the concept of the coefficient of friction. Friction jumps up every time matter contacts matter, but the magnitude depends on several things including the nature of the surfaces and the normal force that acts on the object. Static friction always has a larger value for a given situation than kinetic friction and Tuesday's lab will let you explore that in detail. For your homework problems - they're not hard per se, but they tend to require a number of steps to accomplish. Take your time, sketch things out, watch for applied forces being implemented at an angle and consider how that affects the normal force, frictional resistance and net force acting on the object. We'll go over these on Wednesday before touching on air resistance.

C Block conducted a lab on static and kinetic friction and saw clearly how force applied to an object does not necessarily make an object move. You must exceed the maximum amount of static friction the system can produce before motion can occur. Up until that point the value for applied force is balanced by the static friction, so the object stays in equilibrium. Once F_s,max has been exceeded, the object begins moving, but is still subject to kinetic friction. From your data you will be calculating the frictional force acting on your blocks, the coefficient of friction between the block and reflecting on the nature of forces in motion as you move through the analysis questions and write-up. The lab isn't due until Wednesday, so be prepared on Tuesday to ask me any questions you might have about the lab. We'll go over it in a general way, but you need to tell me if you need specific help with a question or calculation.

E Block took up the ideas of weight and the normal force, which will propel us into a discussion of friction on Tuesday. Remember that the magnitudes of weight and the normal force are only equal if the object is on a flat, horizontal surface. Otherwise, F_Nis only a component of the object's weight. Also, the normal force is affected by applied forces if they act in or have a component that acts perpendicular to the surface. Keep an eye out for those problems and don't forget to add of subtract that value into your calculations. On Tuesday, we'll take up a discussion of friction and you will need to work with both weight and the normal force to successfully manage situations where we include frictional resistance.

F Block started the period by going over Newton's 3rd Law of Motion. When one object contacts another, two forces are immediately and simultaneously generated, equal in magnitude and opposite in direction to each other. To determine the behavior of the objects after the contact, you have to bring those forces into Newton's 2nd Law of Motion and, with the objects' inertia, calculate the resulting acceleration on each object. We then looked at weight, which is easy to confuse with mass, but is something very different. Mass is an inherent property of matter, but weight varies with location since acceleration due to gravity is location-dependent. Weight is a force, reported in Newtons, so make sure that mass is in kilograms and acceleration is in m/s² when you calculate an object's weight. On Tuesday, we'll tackle the normal force and might dip toes into the area of friction.

Have a great long weekend!

RIP Steve Jobs

Love him or hate him, the man was smart, savvy, hard-working and left a massive stamp on our culture... I'm gonna miss the guy...

Gotta Love that Newton

Today was filled with Newton's Laws of Motion, with some weight and normal force thrown in for color.

B and C Blocks reviewed their N-2 and N-3 homework, then moved into a discussion of weight and the normal force. Keep in mind when working problems that mass is not weight - you cannot stick an object's mass into a problem when weight is the necessary property. Also, watch out for problems where the situation does not take place on Earth or is in a location on Earth where they provide a specific value for gravitational acceleration. Then "g" will be whatever the value is for that location and not the familiar 9.81 m/s². A good calculation of weight is critical when assigning a value for normal force in a problem. A surface responds to the push applied on it by an object, so we need the size of that push to determine the response. For horizontal surfaces, F_N = F_g. Easy as pie. On an incline; however, because the normal line to the surface is not parallel to the direction of weight, only a portion of that weight generates a responding normal force: F_N = mgcosΘ. The other component of the weight - mgsinΘ - acts to accelerate the object down the ramp and factors in when assessing motion of the object up or down the ramp. Normal force, itself, plays a starring role in determining role in the frictional force an object experiences, so we will take time to make sure we can accurately calculate the normal force acting on an object before we start to tackle friction. The lab you guys will run for this unit will investigate friction in detail, so that should help clarify a lot of the concepts we'll discuss in class.

E and F Blocks had a discussion of Newton's Laws of Motion, with E Block making it through Newton's 3rd Law and F Block making it through Newton's 2nd Law. We'll pick up with weight and the normal force for E Block tomorrow and conquer Newton's 3rd Law of Motion and weight for F Block.

A Day of Days

Between the storm that left everyone sodden and full day of forces, I'm ready for a nap...

B and C Blocks took time to discuss Newton's 2nd and 3rd Laws of Motion. Many people think of Newton's 2nd Law of Motion purely as the formula F_net = ma; however, that's a little shallow. From an equation standpoint, you should really think of it as a = F_net/m. An object's acceleration is directly proportional to the net applied force and inversely proportional to the object's inertia (measured by the mass). For a single object - increase F_net and the acceleration increases proportionally. For a given magnitude of force, the larger the mass of the object, the smaller the resultant acceleration. The equation is fine for calculations, but keep the general concept in mind, too. It can make general predictions and comparing objects in similar circumstances simple to do.

Newton's 3rd Law of Motion is one that seems so simple, but people really just don't get it. The phrase "for every action, there is an equal and opposite reaction" is so misused, I have to take a lie down sometimes. Newton-3 only deals with the size and direction of forces that arise when objects contact each other. Period. End of it. Finished. No farther you shall go... If it hit a desk with 20N of force downward, the desk applies a 20N upward force on me. If I want to take things a step further and predict what will happen to the motion of the desk and/or my hand after the contact, I have to haul out Newton-2. I know the magnitudes and directions of the forces, now, I have to work with each object's mass to determine their acceleration. Newton-3 does not, in any way, speak to the responses of the objects to the forces. Also, remember that the forces are simultaneously applied - there is no lag time, even though the term "action-reaction forces" is frequently used. Hopefully, today's demonstrations helped solidify a little of this in your minds and you bring the ideas with you to class tomorrow, when we take up looking at specific forces - weight and friction.

E Block conducted their Atwood's Machine lab and, for the conclusion section of your write-up, make sure to consider our discussion yesterday of forces, equilibrium, inertia and Newton's 1st Law of Motion. The wise student might peek ahead to Newton-2 and Newton-3 for additional information to include in your synopsis.

F Block discussed their Atwood's Machine lab and used that to highlight ideas about forces. The concepts of net force, equilibrium, inertia and Newton's 1st Law of Motion were nicely demonstrated by your lab, as was the bones of Newton's 2nd Law of Motion, which we'll discuss in class tomorrow. For the homework tonight, pull out those vector operations skills... you're gonna need them...