Return from Turkey Day

Honors Physics A started their discussion of rotational dynamics with a look at torque and moment of inertia. Torque – the ability of a force to produce rotation around a specific axis. We have insert that “specific axis” in that phrase since different axes of rotation are easier to spin around than others. That’s where moment of inertia comes into play. Moment of inertia looks at different configurations of mass and describes the resistance of that shape to rotation. Take a single object and try to rotate it in different ways. Some ways are easier than others – that is due to the distribution of mass around the rotational axis. The more of the object’s mass that is close to the rotational axis, the lower the moment of inertia and the easier is the rotation. Tomorrow, we’ll extend these ideas to conquer rotational equilibrium – how do you calculate the forces and torques on objects that exist in equilibrium? For tonight's homework, if I don't have time to update the class website, you can USE THIS LINK for the solutions for Chapter 8 problems.

Physical Science B went over their gravitational potential energy and kinetic energy worksheet. We then discussed the other forms of energy such as chemical, nuclear, heat and electromagnetic. We will spend time with heat and electromagnetic energy later in the year and may get a chance to hit nuclear, time permitting. You will discuss chemical energy in detail in biology and chemistry. Tomorrow, we begin an examination of conservation of energy, concentrating just on kinetic and gravitational potential as our examples. Exam looks like it will fall on Monday, so you should have plenty of time to prepare.

Physical Science E also discussed forms of energy and took time to analyze the nutritional label of a pack of cheese to determine how energy is apportioned between the main biological molecules – fats, carbohydrates and proteins. Most people don’t realize that the calorie is a unit of stored energy – how much work could you do if you ate this food – and that different molecules store different amounts of energy in their chemical bonds. Tomorrow’s lab will center around the conservation of energy, specifically mechanical energy, but know that all energy is conserved regardless of form or type. Some of it does not remain in a form or type usable for work, though, and that’s what we mean when we say that energy is “lost” in a system.

Physics F watched a video on anti-gravity machines and worked with examples of rotational motion. The rheoscopic balls were especially nice for looking at how individual regions of a rigidly rotating object compare for angular and tangential speed. By tomorrow, you should have your film and activity questions completed, as well as the review worksheet. Exam on rotational motion and gravity tomorrow and then onto torque and machines! Physics G reviewed for the exam and worked on their preparation worksheet. Have your worksheet ready for tomorrow, as they will be collected before the exam. For both sections – the formula sheet will have all of the angular motion formulas available, but make sure that you know what all the variables stand for!

Homework

Honors Physics A: Read section 8.2 in the book and complete Practice 8B
Physical Science B: Complete the 12.3 Section Review
Physical Science E: Read lab sheet for tomorrow’s activity. Complete Graphing Activity p. 409 and 12.3 Section Review for Wednesday
Physics F: Complete lab questions and review worksheet. Study for exam.
Physics G: Complete review worksheet. Study for exam.

This is Actually Educational

Half-Day!

A shortened day today due to the impending holiday and the pep rally. Honors Physics went over their torque lab and shared data with the students who missed the lab due to yesterday's band practice. There were also given an optional bonus question to work on over break. Physical Science E (no B today)reviewed their potential and kinetic energy homework problems and will discuss non-mechanical energy when we return. Physics F and G started pulling together loose ends for Tuesday's exam. On Monday, F Block will watch a video about gravity and engage in more exam review; G block will review for the test.

Homework

Honors Physics A: Complete lab write up, if necessary. Work on bonus problem, if desired.
Physical Science B: Complete potential and kinetic energy problem sheet
Physical Science E: Chapter Review item #24
Physics F and G: Review for Tuesday's exam

Have a safe and fun Thanksgiving!

Honors Physics conducted an investigation of torque and rotational equilibrium. It was a wild and wooly experience, such that I made sure that the laptops were safely removed from the lab benches prior to the lab period. When we think about balance, we are thinking about torque and rotational equilibrium. Those amazing mobiles that people construct are based on these principles. Keep the net torque on the system at zero and there will be no rotation. Masses are carefully placed to generate equal positive and negative torque. We also have to consider linear equilibrium, though. The pieces can’t snap the strings! The second part of the lab had you pull both equilibria together in what looked like a physics version of Twister. However, with effort, rotational and translational equilibrium was attained and the meter sticks finally behaved themselves. We’ll discuss the lab tomorrow and look more deeply into the idea of torque. Here’s a couple of preview videos if you just can’t wait:





Physical Science B went over their lab investigations and discussed their lab data in light of our work with machines. Maximize the separation between the input and output distances and you maximize the mechanical advantage of the machine. Also, don’t expect efficiency to be great – that is one of the tragic costs of using machines. It costs you more work to do the job with a machine than if you had simply done it yourself. Then, we turned our attention to energy and examined gravitational potential and kinetic energies. Is energy stored or is it actively fueling work? Regardless, it is still energy, measured in Joules. The practice worksheet will allow you to work with the GPE and KE formulas and we will go over them on Monday. The answer key is online and can be accessed THROUGH THIS LINK.

Physical Science E went over their kinetic energy homework and, after a review of GPE and KE, worked on a problem set for both energy types. The answer key is online (see the link above) and we’ll go over the work tomorrow in class. Also, as promised, here are a couple of energy videos:





Physics F and G discussed gravity and factors that affect the magnitude of the force of gravity between objects. Mass and distance are the players , with distance having more of an impact than mass. That pesky r²…double the mass, you only double for the force. Double the distance and the gravitational attraction drops to 1/4 the original value. Remember when working problems that when you solve for distance, makes sure that you are solving for distance and not distance-squared. Too often, folks forget to take that final square-root and end up with the wrong answer. Remember that we are looking at next Tuesday as your assessment day. That gives us a couple of review days between now and then, so prepare any questions you have to address in class.
Homework:

Honors Physics A: Complete lab write up
Physical Science B and E: Complete energy problems worksheet.
Physics F and G: Practice 7I #1,2 and Chapter Review items #31, 35, 39, 50

Simple Machine Videos

Here are some videos for Physical Science dealing with work and simple machines. I'll put a couple about energy up tomorrow:









Mechanical Advantage and Friction:

Countdown to Thanksgiving

Honors Physics sat through a quiz on rotational motion and gravity and then got a brief introduction to the concept of torque. The next chapter deals with rotational dynamics and we will move through the same topics that we covered when we looked at dynamics for linear motion. Tomorrow’s lab will focus on the nature of torque and its relationship to balance. Then, the lab will introduce a new perspective on equilibrium. We have been viewing equilibrium as a situation when an object experiences zero net force. However, a ball could experience zero net force (not moving across the ground), but still be rotating. There is another condition of equilibrium, where an object experiences zero net torque that also has to taken into account for rotating objects. Both conditions of equilibrium will be examined in the second part of tomorrow’s lab.

Physical Science B conducted a lab that investigated simple inclined planes and simple levers. Students calculated mechanical advantage and efficiency and tested how changing angle of incline and lever type affected these descriptors. Groups found that increasing the angle for a ramp decreases mechanical advantage – you are having to work against a larger component of the object’s weight as you raise the ramp. For levers, it was pretty quickly seen that even for the same class of lever, changing the positions of the resistance and effort forces had a big impact on mechanical advantage. Think about first class levers like crowbars and shovels in terms of what you learned in lab – why are these tools built the way they are? We’ll go over this lab tomorrow and begin our discussion of energy.

Physical Science E began their investigation of unit by reviewing the basic definition and unit for energy and differentiating kinetic and potential energy. We spent the bulk of the time discussing gravitational potential energy and practicing using the GPE formula. Remember that height is relative for this calculation and you must state or recognize the zero level for height measurement. Also, be mindful of sign…We breezed over elastic potential energy, although it is another stored energy of position. For EPE, the amount of stored energy is dependent of the amount of stretch or compression and how stiff/loose is the elastic material. We’ll go more into this type of energy in Grade 11-12 physics classes.

Physics F and G discussed the fabulous Randolph and used the discussion to review over basic descriptors and calculations relating to circular motion. We then focused in on the different types of forces that can be responsible for circular motion, which will lead us into tomorrow’s discussion of gravity. I’m looking at the assessment for this chapter when we return from Thanksgiving break – probably Tuesday – so keep that in mind for planning your time.

Homework

Honors Physics A: 8.1 Section Review and Practice 8A
Physical Science B: Complete lab write up
Physical Science E: Read p. 394-395 and complete the Practice on p. 395
Physics F and G: Conceptual Challenge p. 262, Practice 7H #1 and 4, Chapter Review items #32, 34.

A Deep Philosophical Question

Flyin' Pigs!

Randolph the Flying Pig was in the house today to drive junior and senior physics disciples crazy. Honors Physics, Physics F and G were tasked to calculate the centripetal force and tension in the string for Randolph while he flew around in a majestic circle. Without any help from me, since I was napping, they had to decide what variables to measure and how to perform the relevant calculations. It was a free-for-all: no lab groups, just anyone working with anyone to get the job done. On Monday, we will go over the activity and talk about the strategies people employed to get their answers. Honors Physics – don’t forget about your Chapter 7 quiz on Monday, also.

Physical Science B and E completed their discussion of simple and compound machines. We concentrated on the inclined plane family today and discussed the function of and examples of simple inclined planes, wedges and screws. Again, I would say take the time this weekend to try and label household items as to the type(s) of simple machines they represent. You might be surprised at what you find! On Monday, Physical Science B will conduct a lab investigation on inclined planes and levers. Physical Science E will start their discussion of energy.

P.S. Maggie N. - You looked FABULOUS today ;-)

Homework

Honors Physics A: Study for Chapter 7 quiz. Work on Randolph issue.
Physical Science B: Read lab sheet. Complete 12.2 Section Review by Tuesday
Physical Science E: Read pgs. 391-393 and complete the Practice on p. 393
Physics F and Physics G: Reflect on Randolph and be ready to continue our discussion of circular motion on Monday.

A day back after a half day is always tough, but everyone muddled through.

Honors Physics A grabbed gravity today and discussed the factors that affect the magnitude of gravitational attraction between two bodies. All matter generates gravity, but the magnitude of the attraction between objects depends directly on the masses of the objects and inversely on the distance between them. Distance is the bigger player, as the relationship is an inverse-square one. A change in mass has less of an effect on gravitational attraction than an equal change in distance. We’ll go over the gravity homework tomorrow and use the remaining class time to review for Monday’s quiz on rotational motion.

Physical Science B reviewed the function of machines and how machines achieve mechanical advantage by manipulating either input force or distance. They then jumped into the specific types of machines, concentrating first on the lever family. We went over the three classes of basic levers, types of pulleys and wheel and axle systems. You might take time today to look around you and see if you can identify the different classes of levers in everyday objects. Tomorrow, we will go over the inclined plane family and the lab that you do on Monday will look at both machine families by letting you investigate simple inclined planes and the three classes of levers.

Physical Science E began their discussion of machines with an overview of the basic function of machines and how machines provide mechanical advantage. They then began to discuss the lever family of simple machines, exploring simple levers and pulleys. Tomorrow, we will finish up the lever family with a discussion about the wheel and axle and then tackle the inclined plane family.

Physics F and G worked on test corrections and/or lab write ups. Tomorrow, we dive deeper into centripetal force and how it affects the motion of matter.

Homework

Honors Physics A: Practice 7I and Chapter Review items #31, 35, 40
Physical Science B: Chapter 12 Review items #28, 29, 31, 32
Physical Science E: Complete the 12.2 Section Review
Physics F and G: Complete test corrections/labs

Cool Points if You Recognize the Reference

PTC Round 1

Very little to report today, as only two classes met due to early release for parent-teacher conferences. Honors Physics discussed the nature and action of centripetal force and took class time to work through some thought questions centering on centripetal force and circular motion. Tomorrow, gravity! Physical Science B examined the basic definition of machines and what machines can do with force and distance to make work easier. Remember, nothing comes for free – for every multiplication given to you by a machine, it lessens something else. Multiply force, lose distance; multiply distance lose force. Because of this inverse relationship, the formulas for calculating mechanical advantage (MA) are flip-flopped. MA = F_o/F_i or d_i/d_o. Starting tomorrow, we begin to examine the specific simple machines and how they manipulate force and distance to perform work. For both Physical Science B and E – test corrections due tomorrow.

Homework

Honors Physics A: Chapter Review items #27, 28, 34, 36, 38, 53
Physical Science B: Complete test corrections

Honors Physics went over their Chapter 6 exams and then moved into the tangential speed and acceleration associated with rotational motion. The variation in tangential speeds between inner and outer regions of a rigidly-rotating body are what make the consistent angular speeds possible. We then added a third acceleration to the mix – centripetal acceleration. Directed towards the center of the rotation, centripetal acceleration takes the job of changing the direction of motion and keeping objects moving in a circle. The speed of the motion is handled by the tangential acceleration. So, two different accelerations work to produce the velocity changes – tangential for speed, centripetal for direction. Tomorrow, we discuss the forces that produce centripetal acceleration – centripetal force – and demonstrate how different forces can take on that role for circular motion.

Physical Science B and E went over their fluid forces exam. For this exam only, since it was pretty math-heavy and much of the material was not in the textbook (although it was in the class notes), I am allowing test corrections. As stated in class – for conceptual questions, tell me why you chose the wrong answer and explain why the correct answer is actually correct; for problems - show the work to solve the problem correctly and discuss why you got the problem wrong in the first place. For each item you correct correctly, I’ll give you back one-half of the points you missed. For both classes, get all the help you need from me, parents and friends, but have the corrections to me on Thursday.

Physics F conducted their centripetal force lab. You will have time in class tomorrow to complete the lab and its write up, but you might spend a little time tonight organizing your data to make tomorrow run more efficiently.

Physics G completed their work on the centripetal force lab. For two different constant radii, an increase in the centripetal force required a higher tangential velocity for the motion to proceed. Comparing trials with the same mass, the larger radius required a higher tangential velocity to keep the motion going. We will review tangential and angular speeds and accelerations tomorrow and toss centripetal acceleration and centripetal force in to the mix.

Homework

Honors Physics A: Complete Practice 7G and 7H
Physical Science B and E: Work on test corrections
Physics F: None
Physics G: Complete the 7.2 Section Review and p. 270 # 17,18,20

No, I Don't Know When Report Cards Come Out

I'm not sure if people are enthusiastic or apprehensive about getting their quarterly marks, but believe me when I say that once my grades are turned in, report card duties are out of my hands...

Honors Physics reviewed their centripetal force lab and results varied, as expected. Most groups found good relationships between the measured centripetal force and the calculated centripetal force, but there were significant sources of error possible, depending on your setup. We then turned attention towards defining and calculating basic descriptors of circular motion – displacement, speed and acceleration – and discussed how these values were analogous to their linear counterparts. This is important to keep in mind as we move through this unit – if you get stuck trying to figure out how to calculate something, think about how you would calculate the linear variety of the property and rewrite with angular equivalents. Tomorrow, tackling tangential speed and two more accelerations!

Physical Science B and E were introduced to the concepts of work and power today and the formulas for solving problems in these areas. Remember that for work to be done by a force there has to be displacement and the force itself had to cause or act in a direction opposite the displacement. We contrasted lifting an object (work is done by your arms) with carrying an object (work is not done by your arms) and examined examples of positive and negative work. For power, make sure that you are very clear that power is the rate at which work is done/energy is transformed. Machines with different power ratings can do the same amount of work – the higher power machine just does it in less time. For problem solving, it is quite common to first have to calculate the work done on or by an object and then use that value for your power calculation. It could go even further than that – you might have to calculate distance and/or force first and then calculate work before solving for power. Just remember to work backwards – what do you need to solve for, what do you need to solve for that variable, what do you need to solve for the variables necessary for the final solution, etc. Plan your attack and if it doesn’t work, try something else until you find the correct method.

Physics F reviewed basic descriptors of rotational motion and then moved into tangential speed and acceleration. Whereas angular speed and acceleration are the same for all points on a rigidly rotating body, tangential speed and acceleration change with different points. In fact, they have to change in order to keep the angular quantities the same! We then looked at the idea of centripetal acceleration – the acceleration involved in the change of direction characteristic of circular motion. Tomorrow’s lab will allow you to measure centripetal acceleration and the force that produced it (centripetal force) and test which variables affect their magnitude.

Physics G conducted their centripetal force lab and no one received a concussion – score! By measuring period and radius of a rotating object, calculations of centripetal acceleration can be conducted. Combined with the mass of the washers, centripetal force could be established. Radius and mass were varied and their effects on centripetal force was noted and graphed. We will discuss centripetal acceleration tomorrow and also the linear quantities of tangential velocity and acceleration. Have your labs completed so that we can discuss them as part of class.

Homework

Honors Physics A: Practice 7D, practice 7E #4, Practice 7F #2,3
Physical Science B and E: Complete Practice and Section Review questions/problems on page 284
Physics F: Complete the 7.2 Section Review and p. 270 # 17,18,20
Physics G: None. We will work on the lab in class tomorrow

Friday the 13th!

Gloomy, clammy but no murderers wearing hockey masks. I'll give the day an "E" for effort...

Honors Physics conducted a lab investigation that was a little off our regular protocol. Rather than a detailed lab sheet, the basic technique was described, but the actual details of the apparatus and experimental protocol was left up to the students (especially for testing other variables). Groups had to use a motion detector and force sensor to assess the centripetal force on a pendulum system and relate it to the tangential velocity, pendulum mass and radius. Does F_c = mv_t²/r? After the basic experiment, students had to change the mass, radius and displacement variables and see if they affected the relationship and/or the magnitude of the centripetal force. On Monday, we will discuss the lab and jump headlong into angular motion.

Physical Science B and F endured their forces in fluids test. Scores were on the low side, for both the conceptual questions and the math problems. We will go over the exams next week and work to firm up the information in people’s minds. Also on Monday, we begin our study of work, power and simple machines. Make sure to have the homework problems completed and Physical Science B should have their lab write up prepared.

Physics F and G worked on understanding the nature of the radian and how we use radians to discuss displacement in circular motion. Students conducted a brief activity to see how the value of a radian is determined, using wire and circles drawn with a compass. Sure enough, it takes about six and a quarter lengths of wire, each the length of the radius off a circle, to cover the circle’s circumference. The angle swept out by one of those pieces of wire equals one radian. A full circle equals 2π radians. Work to drill the concept of radians and how to work with them in problems (and on your calculator) into your brain. For the next two chapters, displacement of objects engaged in circular motion will need to be in radians to analyze the motion mathematically.

Homework

Honors Physics A: Complete lab write up
Physical Science B: Complete lab write up. Complete practice problems on page 379 and 381
Physical Science E: Complete practice problems on page 379 and 381
Physics F and G: Physics G should read their lab sheet, Physics F has no homework

A Case of the Mondays

Pretty much everyone today said it felt like a Monday. Know what? They're right...

Honors Physics , Physics F and G engaged in their Chapter 6 graded learning experience today and will move on to circular motion tomorrow. We have been neglecting the fact that many objects revolve or rotate, even when experiencing linear motion. The next two chapters will allow students the opportunity to examine rotational motion and incorporate that material into their overall examination of mechanics. In Chapter 7, descriptors of circular motion will be introduced, as will the nature of the forces involved in maintaining circular motion. The lab for this unit will focus on centripetal force, how it can be measured and what factors affect the magnitude of the centripetal force an object in circular motion experiences. Honors Physics works on that tomorrow, and Physics F and G will conduct the investigation on Monday and Tuesday. One point to note about this unit: make sure that your calculator is set to receive measurements in radians, not degrees. Ask me for help if you have need. When we work with displacement for rotational motion, the proper value is in radians – another way, besides degrees, to report fractions of a circle. If you have yet to work with radians and the unit circle in math, we’ll do a bit of review at the beginning of the unit which should bring you up to speed.

Physical Science B worked on their buoyant forces lab and got quality results for congruence between apparent loss of weight by an object and weight of water displaced by the object. Their calculated values were pretty close to the measured values, not exact, but there is always a margin for error in experiments. Then, they had a bit of time at the end of the period to review material for tomorrow’s exam, which was what Physical Science E worked on all period. Some of the math required for this section is not on the MCAS formula sheet, so I’ll have those additional formulas available for you tomorrow. For both sections, study the textbook, notes and worksheets and please don’t forget your calculators. Here is a worksheet with more practice problems for hydraulics, pressure at depth and buoyant forces.
P.S. Mikaela D - found your Buoyant Forces lab sheet (was caught in the staple of another student's work).

Homework

Honors Physics A: Read lab sheet. Complete 7A #1-3, 7B #1-3 and 7C #1,2 by Monday
Physical Science B: Complete lab write up by Monday. Study for tomorrow’s exam
Physical Science E: Study for tomorrow’s exam
Physics F and G: Read 7.1 in the book and complete p. 252 #1 and p. 269 #1-5

Exam Prep Tuesday

Honors Physics, Physics F and G worked on review for their Chapter 6 exam, which is scheduled for Thursday. Be able to work with momentum and momentum change of single objects, the impulse-momentum theorem and conservation of momentum and kinetic energy for a system. On Friday, we change gears somewhat and begin our unit on circular motion. Honors Physics will engage in a lab investigation that allows students to explore factors affecting the centripetal force acting on an object in circular motion and how aspects of translational motion can be used to calculate centripetal force and acceleration.

Physical Science B reviewed their self-created fluids problems. Thanks to Haley, Courtney and Cara for volunteering to put their problems on the board and walk through the solutions with the class. Tonight, add on a problem for hydraulics devices, to make sure that you can evaluate those systems, as well. On Thursday, students will conduct a lab investigation centering on Archimedes Principle and buoyant forces. There will also be time allotted to address any questions prior to Friday’s exam.

Physical Science E discussed Bernoulli’s Principle and everyday examples of Bernoulli’s Principle in action. We analyzed flight, smoke rising in a chimney, perfume atomizer function and kite flying in terms of Bernoulli’s Principle and did a couple of demonstrations, to boot. On Thursday, review time for Friday’s exam. Come prepared with questions so that we can address them as a class.

Homework

Honors Physics A: Review for exam
Physical Science B: Create a unique hydraulics device problem
Physical Science E: None
Physics F and G: Review for exam

Oh No! Snow!

Every year I hope and hope that we'll have a snowless winter - something that would suit my Southern blood perfectly. And every year, my hopes are dashed. Stupid Mother Nature...

Honors Physics reviewed the elastic, inelastic and perfectly inelastic collisions and then jumped into a mish-mash of problems that require the use of skills dating back to the beginning of the course. Such is the way of physics…keep in mind your studies of kinematics, conservation of energy, projectile motion and make use of any tools in your academic tool bag to jump on these problems. We’ll go over them on Monday, but the link to the solutions are still on the blog post a few days ago. General review after we discuss these problems and then exam on Tuesday.

Physical Science B completed their overview o f buoyancy with a discussion of the homework questions. It was good to hear people thinking in terms of forces and pulling together succinct answers for the questions. We then turned our attention to Bernoulli’s Principle – the pressure in a fluid is inversely proportional to the velocity of the fluid. We linked this to conservation of energy, which we will take up in more detail in the next chapter. Bernoulli’s Principle combined with the nature of fluids to move from areas of high pressure to areas of low pressure has some interesting effects that we observe in daily life, like smoke rising up a chimney, assisting in flight, allowing perfume atomizers to work, etc. A few examples of Bernoulli’s principle were demonstrated in class. Note to parents: I am not responsible if your child goes home and sprays water all over your house to show you what he/she learned in school today.

Physical Science E conducted a lab investigation on buoyant forces. Students directly measured the apparent loss of weight by an object submerged in a fluid, the weight of the displaced fluid and calculated the theoretical buoyant force using the volume of an object and the density of fresh water. Groups obtained good results: the apparent weight loss was close to the weight of the displaced fluid which was pretty close to the calculated buoyant force. It was clear, based on the direction of the net force acting on the object, why the 500-gram mass and rock sank, but the wood floated. On Monday, we will discuss Bernoulli’s Principle. For both B and E Blocks, start looking for a test at the end of next week. The likely day is Thursday, but if people need more math practice, we might have to move it to Friday.

Physics F and G discussed the types of collisions in which objects can engage and how well kinetic energy is conserved in each type. Elastic collisions are good at conserving kinetic energy, but most collisions show definite kinetic energy losses due to deformation of objects, sound production, and internal energy increases. Assume in problem solving that if a collision is not elastic (pure conservation of kinetic energy, objects separate after collision) that a collision is perfectly inelastic (objects stick together as a single object and demonstrate kinetic energy loss). On Monday we will begin reviewing for the momentum exam, which looks like it is going to fall on Thursday, so take time to review the chapter this weekend and pull together a list of questions that you would like to go over next week.

Homework

Honors Physics A: Chapter Review items #27-30, 32, 45, 46, 52, 54, 57
Physical Science B: None
Physical Science E: Complete lab write up
Physics F: p. 230 #2,4 and Chapter Review #27-31
Physics G: None

Conserving Momentum

Honors Physics reviewed conservation of momentum and then turned to the classes of collisions. Even though all collisions are marked by conservation of momentum, not all collisions (actually a puny proportion) will be marked by conservation of kinetic energy. Elastic collisions – no deformation of objects, no sticking together, no loss of energy to sound or internal energy – they just don’t happen on a regular basis. Some collisions get pretty close, like a hard rubber ball bouncing on a smooth marble floor, but most collisions won’t proceed with no deformation or loss of energy to a nonmechanical form. The other side of the spectrum is also rare: the perfectly inelastic collision. Objects sticking together completely and moving as one discrete unit does not describe most collisions. Normally, we see things in between these extremes and these collisions, the inelastic variety, form the bulk of common experience. For our purposes, collisions will either be elastic or perfectly inelastic and this is the types of collisions you’ll find in the homework problems tonight. Tomorrow, we’ll go over those problems and work on some mixed review material to start preparing for Tuesday’s exam.

Physical Science B and E went over their Archimedes’ Principle problems and completed their discussion of density and buoyancy. Students had time to work on some conceptual questions concerning buoyancy and Physical Science E will conduct a lab investigation tomorrow that will allow them to examine buoyancy in more detail. They will get the opportunity to measure apparent losses of weight, weight of displaced fluid and calculate the theoretical buoyant force acting on an object. Physical Science B will begin a discussion of Bernoulli’s Principle tomorrow – the motion of fluids from high to low pressure and how that motion can affect the motion of objects in the path of the fluid.

Physics F conducted the impulse-momentum lab and got results comparable to Physics G. The impulse on an object approximated, in most cases, the change of momentum of the cart and looser elastic materials showed a marked longer time interval for the momentum change to occur than did stiffer elastic materials. The force-time graph showed a shallow “hill” for the impulse acting on the object for loose elastics and a sharp peak for more elastic materials. Consider that when thinking about forces that you experience in daily life and how you could increase or reduce the size of those forces by using time.

Physics G discussed conservation of momentum – the total momentum of a system stays the same, although the momentum of individual objects in the system can change. We explored different types of interactions within systems and how momentum was conserved in each case. Tomorrow, we will discuss the different classes of collisions and emphasize that momentum is conserved for each class. Kinetic energy, though…that’s another story.

Homework

Honors Physics A: 6E and 6G. For 6G, only complete the Part B portion for number 1. You can skip it for the rest of the questions.

Physical Science B: Complete buoyancy questions
Physical Science E: Read lab protocol sheet and complete buoyancy questions
Physics F: Complete lab write up
Physics G: Read 6.3 and complete the 6.3 Section Review #2, 4 and Chapter Review #27-30

The Frost is on the Pumpkin

As the temperatures fall, start carrying around an extra jacket in your backpack. You are going to find that some classrooms will be like Antarctica and others will more resemble Death Valley. Make sure that you can vary your layers accordingly...

Honors Physics reviewed their impulse-momentum labs today and related the results to what we already know about applied and restoring forces of elastic materials. We then turned our attention to conservation of momentum and how Newton's Third of Motion and the impulse-momentum theorem lead to the conservation of momentum in systems. I haven't had a chance to update the course website lately, so I'll put a link to the momentum chapter solutions here so that you can check your work from home. Tomorrow, we'll go over the homework problems and then toss a look back to energy and track the conservation (or lack thereof) of kinetic energy in collisions.

Physical Science B and E reviewed Archimedes Principle and then spent time practicing the mathematical applications of buoyancy. Your homework problems should, like all word problems, thought of as puzzles or mysteries. How do you take what you are given and expected to know and use it to find the answer? Try one technique and if that leads nowhere, try something else. Things to remember when working buoyancy problems:

• The volume of the object is equal to the volume of the displaced fluid.


• The mass of the object and the displaced fluid must be in kilograms in order to calculate weight in Newtons


• The density formula can be used to calculate mass, volume or density of either the object or the displaced fluid. Consider how to use this formula with the information given in the problem to help you along towards the solution.

The answers for your homework problems:

1. F_g = 2.7 x 10⁵ N; F_b = 4.4 x 10⁸ N; object floats


2. F_g = 1.82 N; F_b = 0.15 N; object sinks


3. F_g = 73 N; F_b = 2.2 x 10³ N; object floats; density = 0.17 kg/m³


4. F_g = 11.8 N; F_b = 4.6 N; object sinks; density = 11 g/cm³

Physics F discussed conservation of momentum and how this principle can be used to analyze motion in multi-body systems. Keep in mind that the total momentum of a systems is conserved, but the momentum of individual objects in the system will change after the collision. We related Newton's 3^rd Law of Motion and the impulse-momentum theorem to explain why conservation of momentum holds true and the pattern of momentum change in collisions. Tomorrow's lab will let you analyze momentum and impulse in more detail.

Physics G conducted a lab that concentrated on the impulse-momentum theorem. The agreement between the impulse delivered on an object and the object's momentum change was tested, as was the effect of elasticity on the impulse delivered by a material. We will go over this lab tomorrow and then take on the concept of conservation of momentum.

Homework

Honors Physics A: Practice 6D and 6.2 SR #2,4
Physical Science B and E: Archimedes' Principle problem sheet
Physics F: Read lab protocol sheet
Physics G: Complete lab write up

Honors Physics conducted a lab investigation that focused on the impulse-momentum theorem. The impulse (FΔt) an object experiences is equal to the object’s change in momentum (Δp). A force sensor and motion detector was used, which allowed measurements of force, time and velocity to be taken and used to check how momentum change corresponded to the impulse delivered by an elastic material. Groups got some choice as to the type of elastic material used and it was quickly evident that stiff materials delivered a greater impulse to the carts than did looser materials (given the same push to the cart). We will go over the lab in class tomorrow and begin our discussion of conservation of momentum.

Physical Science B reviewed their pressure/depth lab and then went over the homework problems that had tasked them to use the pressure formula that they later derived from the lab activity. Folks seem to have done a good job with these problems – keep in mind which variables are constants, which information (such as density) that is given in a problem can be carried to other problems, and which direction you choose (up or down) to be positive/negative. Students then began to examine the concept of buoyancy, Archimedes’ Principle and the nature of buoyant force. The role of the buoyant force in promoting floating or sinking was discussed and the link between density and the magnitude of the buoyant force (and weight of the object) was investigated. Physical Science E also went over their pressure/depth problems and moved through the concept of buoyancy.

Physics F and G worked on correcting their work/energy exams. Grades were a bit low on this test across the board, so make sure to take care with your corrections that you understand your mistakes. The midterm and final are both cumulative, so you will definitely see this information again.

Homework

Honors Physics: Complete lab write up
Physical Science B and E: None
Physics F and G: Complete test corrections

Force and Momentum

Honors Physics began their discussion of momentum with an overview of impulse and the impulse-momentum theorem. I emphasized today and will reiterate it again to keep a close eye on the signs for velocity. Momentum is a vector, and takes the direction of the object’s velocity. Momentum change takes into account a change in both the direction and magnitude of the velocity, so watch closely how you set up your equations. Tomorrow’s lab activity will allow you to measure the impulse on an object and compare it to the change of momentum the object experiences. We’ll use a variety of elastic materials for your tests so that you can demonstrate and reflect upon the importance of choosing proper materials in construction, engineering and manufacturing.

Physical Science B conducted a lab activity that allowed them to examine the relationship between depth and fluid pressure. As we discussed in class, with greater depth comes greater pressure in a body of fluid. For the same area (the opening of the tubing, in this case), greater depth means a greater weight of fluid pressing down on the mass. Voila! Greater pressure. The mathematical relationship that you worked out in the expression told you that the pressure change was constant – the relationship was linear – and that the equation of the line you derived matched the equation for pressure/depth that we worked with in class on Friday. Tomorrow, another aspect of forces generated by fluids: buoyancy.

Physical Science E went over their Pascal’s Principle homework problems and we reviewed Pascal’s Principle before moving on to the changes in fluid pressure with depth. Using last week’s lab as an example, we discussed the equation used to calculate fluid pressure at any depth in any fluid and worked on practice problems using this formula. We’ll go over those tomorrow and then move on to the concept of buoyancy.

Physics F and G worked on test corrections. Make sure for your corrections that you show all work and explain for questions why the correct answer is actually the correct choice. Some folks are getting a little lazy about doing their corrections and I am going to stop accepting corrections that are not submitted with the proper information. Same goes for homework – homework should be completed and show all work. A few people are trying to submit homework that does not show work and/or does not show the required corrections. That is going to come around to bite you, so get back on track, pronto!

Homework

Honors Physics: Read lab sheet
Physical Science B: Complete lab write up
Physical Science E: Pressure As a Function of Depth problem worksheet
Physics F and G: p. 233 #17-24