Class 69.5:

Warm Up: 

1.  How does a Van de Graaff Generator Work?

2.  What can we do with a VDG?

Today:

• Return retakes and group test corrections.

• Last chance to turn in group test corrections.

• Check/review homework --  Unit 9, "Electrostatics Lite" handout. PDF  Unit 9 Handout Key

  • PhET Balloons Simulation

  • John Travoltage Simulation

• Van de Graaff experiments/demos

• VDG Links:

  • MIT video --  VDG demo

  • Good, detailed explanation of Van de Graaff, plus link to demos  direct link to demos, etc.

  • More about how a VDG works

• VDG Things to try (at some point):

• Hair-raising

• Pith ball

• "Hero Engine"

• Putting out fire

• Lightning rods

• Fluorescent bulb

• VDG vs the sniffer

Class 69:

Warm Up:  Which proposition is most certain?

Today:

• Test retake

• Turn in your group test corrections if you want them graded by tomorrow.

• Complete the homework due tomorrow.

Class 68.5:

Warm Up: 

Today:

• Notes p. 4-5 (conductors, insulators, ground, induction, polarization...)  2019 video   Unit 9 Handout Key

• Vsauce video -- You can't touch anything

Warm Up: 

1.  What started this fire at a gas station?

2.  What circumstances contributed to the fire?

Today:

Class 67.5:

Warm Up: 

1.  If you rub a balloon on your head and then hold it next to your hair, your hair is attracted to the balloon.  Why? Triboelectric Series

2.  Your hair may also stand on end after being rubbed by a balloon.  Why?

Today:

• Return tests, discuss retake materials
• Test retakes on Thursday.  Group test corrections also due on Thursday.
• Disassemble cars.  Clean and return parts -- axles, bearings, bushings?
• Start new unit

Warm Up: 

Today:

• Test -- Rotational Motion

Class 66.5:

Warm Up:  What do these graphs from last year's contest show us?  How did the outlier (circled in red) go so fast?

Today:

• Announce Rubber Band Car Contest winners -- contest results
• Test Review
  • Formulas
  • Format -- like the practice test, but with different data, and without numbers 12-14 and 16
  • Complete #23 and 24 on the practice test.

• Disassemble or keep your car.

• Turn-in group test corrections by next week.  If your original copy is a mess, attach a clean copy with any new answers.  Double check your answers!!  This is your last chance.

Warm Up:  None

Today:

Warm Up:   A few Important Notes:

1. Add a small data table to part 5 of the group test
2. If you want me to count frames per wheel rotation, email me the shortest trimmed video of your wheel (in 240fps).  I can count frames using Quicktime Player.
3. Enter your raw data (from your data tables) into the spreadsheet provided in Google Classroom.

Today:

Class 65:

Warm Up: 

Today:

• Turn in your group test.  The hard deadline is tomorrow, but you really should have it done today.
• Practice with your car -- if you have time.  Important Note: the scoring formula imposes no penalty for cars that go faster than predicted, so you should make your car go as fast as you can.
• Get your car's speed officially measured.

Warm Up:  A1 -- skim through a moment of inertia instructional video

Today:

• Continue with the group test.  Everything in the group test was on the practice test that you completed last week.  Here's the practice test: PDF Solutions  Spreadsheet with answers but not formulas
• Once you turn in the group test, you can practice with your car if you have time.  Important Note: the scoring formula imposes no penalty for cars that go faster than predicted, so you should make your car go as fast as you can.

Warm Up:  Revisit yesterday's warmup, regarding precise time measurements

Today:

Class 63.5:

Warm Up:  How can we use a phone to accurately, confidently determine time intervals and velocities?

1.  If you're using an iPhone, what should you do first?

2.  How can you precisely measure the time interval of the weight's descent during wheel and axle testing?

3.  How can you precisely measure the top angular speed of a wheel and axle during motor energy output testing?

4.  After you have turned in your group test (and speed prediction), how can you precisely measure your car's top speed?

Today:

• At the same time...
  • Collect moment of inertia data.  Here's a video showing how I did it.
  • Finish your motor. Here's what I think is the simplest method.  You can also add tie a loop at the end of a string; that's probably best for wheel and axle testing.  Here's a video showing how to tie an improved clinch knot (good for tying the end of a string to something).
  • Work on your calculations

Class 63:

Warm Up:  Suppose you want to build a camp fire.  You have plenty of dry wood, but it's all big limbs that are too long to be manageable and too thick to break over your knee.  Without using a saw or an axe, what's the best way to divide the wood into smaller pieces?  Can you describe the proper technique? One solution.

Today:

• Check/review homework.
• Assemble rubber band cars.
• Begin testing your car --
  • Collect Moment of Inertia Data
  • Build your motor and begin testing.  "False starts" are okay, but no complete runs
• Motor design calculator -- Video explaining how it works
• Rubber Band Car Group Test (pdf) is due by the end of class on Thursday.  Don't forget to fill in the data sheet in Google Classroom.
• Rubber band car assembly video -- from last year; similar to this year

Class 62.5:

Warm Up: 

1.  Suppose a single, ordinary rubber band (labeled A in the diagram) requires a force of 8N to stretch it a distance x=20cm.  How far must the other configurations (described below) be stretched in order to have that same tension of 8N? [Assume that the rubber bands behave like ideal springs with a constant k.]

B.  2 rubber bands in "parallel"
C.  2 rubber bands in "series"
D. 1 rubber band, cut and laid out as a single strand

2.  If you stretch each of these configurations from rest position to a max force of 1N, which band will store the most energy? How much energy will each store?  How much space will each take up?

Today:

• Check/review homework
• Design rubber band cars -- choose frame length, wheel sizes and whether or not to have wheel thickeners
  • If you aren't sure that youre wheels and thickeners will fit on the bed, print out the sheet for the frame you would like and the wheels and thickeners you would like.  Then cut out the wheels and thickeners to see if you can fit everything.  FYI, the scale is 28.26%.
    • Frames 8"-16"
    • 20" Frames
    • 23.5" Frames
    • Wheels 2"-5"
    • Wheels 6"-8"
• Submit your order
• Take a look at this if you're interested... Motor design calculator
  • This video explains how it works and how to use it.
  • This video is shorter, in case you're not interested in how it works

Class 62:

Warm Up: 

Today:

• Check/review homework
• Get Rubber Band Car Project Stuff:
  • Overview pdf
  • Car parts buffet.svg
  • Practice test (plus a few extra questions) PDF-- you will be answering most of these with your group, using data you collect from your car.
• Work on the practice test -- form a group if you want (up to 3 members)

Class 61.5:

Warm Up: 

Today:

• Check/review homework
• Unit 8 Handout: Rotational Motion (pdf)
• Notes: Rotational Kinetic Energy (p. 13) Notes Key
Video from 2020 -- skip forward to KE
•  Start 10.5 Angular Momentum Notes (p.15) -- Notes Key -- 2019 video part 1 2019 video part 2

Class 61:

Warm Up:  A sphere, a cylinder, a thin hoop, and a frictionless box are released from rest at the top of ramp.  Their masses and heights are identical.  There is no air resistance, and everything rolls smoothly, so there is no kinetic friction. 

1.  Rank the objects according to their arrival times at the bottom of the ramp.

2.  Suppose the bottom end of the ramp is frictionless, and when they reach the bottom, the objects hit a vertical, frictionless wall.  What motions, if any, would continue after impact?

3.  How would the results be different if some objects had more mass or greater size than others?

4.  How would the results be different if the ramp itself were frictionless?

Today:

• Check/review homework
• Unit 8 Handout: Rotational Motion (pdf)
• Notes:  Video from today's class
  • Notes: Rotational Kinetic Energy (p. 13)
  •  Start 10.5 Angular Momentum Notes (p.15) -- Notes Key --

Class 60.5:

Warm Up: 

Today:

• Check/review homework
• Return retakes
• Unit 8 Handout: Rotational Motion (pdf)
• Notes: The rotational version of F=ma -- Dynamics of Rotation (p. 11).   Video from today's class

Warm Up:  None

Today:

• Optional retake
• Work time -- see homework

Class 59.5:

Warm Up:  Suppose a weight is tied to a string, the string is tied to the axle, and the axle is supported as shown on the right. 

1.  If the string is wound around the axle and the weight is released from rest, what will the system do after that?

2.  How can we find the non-conservative work that is done on the system as the weight bobs down and up?

3.  You'll need this for #11 on the homework... the rotational equivalent of W=Fd is W = ??

4.  This system eventually comes to permanent rest, because there is torque due to friction.  How can we find the magnitude of that torque? [This is like #11 on the homework.]

Today:

• Check/review homework

Class 59:

Warm Up:  Suppose a yoyoer simply lets a yoyo fall and come back up on its own.  The yoyo falls 0.628m in 1s, unwinding string the entire time, and its very thick axle radius somehow remains constant at 0.01m.  The miraculous yoyo is 100% efficient, so it returns to the same height where it started.  During this trip down and back...

1.  What is the angular displacement of the rotating yoyo, in radians?

2.  How many rotations does the yoyo make?

3.  Sketch a graph of the yoyo's angular velocity for the entire trip.

4.  Sketch a graph of the yoyo's linear velocity for the entire trip.  How is this possible?

Today:

• Unit 8 Handout: Rotational Motion (pdf)
• Video from today's Class
• Angular Acceleration and Intro to Rotational Kinematics (p.7)  Notes key 
• Kinematics of Rotation Notes  (p.9) -- Key

Class 58.5:

Warm Up: 

1.  How can you find the mass of a bag of clay by balancing torques?  Your provided materials are an altered meter stick, a string, and a 200g mass?

2.  What is the minimum number of times you need to balance materials in order to find the answer?

Today:

• Unit 8 Handout: Rotational Motion (pdf)
• Angular Acceleration and Intro to Rotational Kinematics (p.7)  Notes key  Video from 2021-22
• Kinematics of Rotation Notes  (p.9) -- Key (2019 video)

Homework:

• None

Class 58:

Warm Up:  Torque is the rotational analog of force.

1.  What are some other rotational rotational versions of the linear quantities we have been using?

Today:

• Momentum/Impulse test retake on Friday
• Get the rest of  the unit handout -- Unit 8 Handout: Rotational Motion (pdf)
  • Notes:  Torque and balancing torques (p. 1-3)   Torque Notes Key
  • Angular Acceleration and Intro to Rotational Kinematics (p.7)  Notes key  Video from 2021-22
• Do you want to make rubber band cars, or should we hurry on to the next unit?

Homework:

• Finish Torque practice, p. 4 through letter A on p.6 (you don't have to do b and c on the last page)   Torque Practice Solutions

Class 57.5:

Warm Up: 

1. What are some options when a bolt or nut is stuck, and you can't loosen it with a wrench?

2.  What's a breaker bar, and how does it work from a physics standpoint? One example

Today:

• Return tests
• Start the new unit -- Rotational Motion -- just torque for now

Homework:

• None   Torque Practice Solutions

Warm Up:  None

Today:

• Test -- Momentum and Impulse

Homework:

• None

Class 56.5:

Warm Up: 

1. What's going to happen when I roll the first sphere until it collides?

2.  What happened?

3.  Why?

Today:

• Review Ballistic pendulum lab  -- Here are the data, including velocities measured by duration between sounds
• Review for test

• Multiple choice
  • Questions and short problems about momentum, impulse, impact force, impact time, coefficient of restitution
  • conservation of momentum (when and how it applies and when it doesn't) and conservation of mechanical energy
  • Odd and ends from notes -- units, elastic/inelastic, impulse as area under curve
  • Collision lab
• About 5 problems
  • Ft = change in momentum = mass x change in velocity
  • p = mv
  • conservation of momentum
  • finding velocity with a ballistic pendulum
  • collision with coefficient of restitution, requiring system of equations
• What do these terms mean, and how do they relate to one another?

	impulse	change in momentum	impact force	impact time	coefficient of restitution
impulse	X
change in momentum	X	X
impact force	X	X	X
impact time	X	X	X	X
coefficient of restitution	X	X	X	X	X

• Preview next unit?
  Unit 8 (Rotational Motion) Handout  (PDF)

 

Homework:

• Test tomorrow.  Get ready.

Class 56:

Warm Up: 

The pictures on the right show a traditional water wheel followed by two Pelton Wheels.  The Pelton wheels extract more energy from the water.  How?

wikipedia (pelton wheel)  Videos: short --Animation longer --Large Hydroelectric Dam Pelton Wheel  and another one in an old mill

Today:

• Check/review homework
• Ballistic pendulum lab -- Use a ballistic pendulum to measure the muzzle velocities of various Nerf launchers.  Collect data and complete the spreadsheet.  Ballistic Pendulum Instructions  (PDF)
• Test on Thursday

Homework:

Class 55.5:

Warm Up:  What will happen when a "big, old" Volvo wagon crashes into a "new, small" Renault Modus.  Which would you prefer to be in?  Why?

Today:

• Check/review homework -- ballistic pendulum problem
• Go over collision lab answers and solutions -- be aware that some of my notes may not account for different choices in signs
• Ballistic Pendulum lab tomorrow
• Work time

Homework:

• P.15-16, problems 1-3 and 5. Solutions

Class 55:

Warm Up:  There are essentially two stages in ballistic pendulum's operation.  First, the projectile collides horizontally with the motionless pendulum.  Then the pendulum and the embedded projectile swing upward on low-friction strings.

For each of these stages, decide whether momentum and mechanical energy are mostly conserved. 

1.  In the collision stage, is momentum conserved?  What about mechanical energy?

2.  In the swing stage, is momentum conserved?  Mechanical energy?

Today:

• Check/review homework
  • A1/2 -- homework I forgot to review yesterday (p.13) Answers
  • Both classes -- p. 14.  Answers
• Do some Ballistic Pendulum notes and calculations (p.5-6) -- to prepare for the homework and ballistic pendulum lab  VIDEO from Class
• Unit 7 Handout: Momentum (PDF)
• Finish the collision lab.  Submit one Cart Collisions Lab for your group in Google Classroom.
• If there's time, complete the group quiz with your group.

Homework:

•  Practice test problem 4 (ballistic pendulum), page 16.  Solution

Class 54.5:

Warm Up:  There are "hard" collisions and "soft" collisions.  There are collisions that are "more bouncy" and "less bouncy." 

Part A:  Consider the following collisions and classify each according according to their positions along two axes: hard/soft and bouncy/not bouncy.

1.  A dropped marble lands in a deep pile of feathers.

2.  A dropped marble lands on an anvil.

3.  A dropped marble lands on a piece of wet clay.

4.  A dropped marble lands on a spring with a low k.

Part B:  The "hardness" or "softness" of an impact, and the "bounciness" of a collision can be understood by considering the concepts of impact force, impact time, coefficient of restitution, momentum, and impulse.

5.  Use the physics terms above to describe how collisions at the same speed can be either hard or soft and either bouncy or not bouncy, depending on the circumstances.

Today:

• Check/review homework
• Work on the lab.  Wrap it up tomorrow.
  • A few notes:
    • Try to keep impact velocity constant
    • For the low e collisions, one should have a lower impact force, and one should have a higher impact force.  They don't have to be super high and super low.

Homework:

• Answer the conceptual questions on page 14.  There's no answer key provided.  Just answer the questions; we will go over them in class.

Class 54:

Warm Up: 

Suppose you start up the Newton's cradle by pulling aside and then releasing one sphere.  As the cradle does its thing...

1. When is the collective momentum of the all of the spheres conserved?  How can you tell?

2.  When is the collective momentum of the spheres not conserved?  How can you tell? Why?

3.  What happens to the total mechanical energy of the spheres during the first collision?

4.  Why is the number of spheres "kicked out" always equal to the number of spheres that initiate the collision?

5.  Would it be possible to build a Newton's cradle that "kicks out" a number of spheres that is different from the number that cause the collision?  If so, how?

Today:

• Unit 7 Handout: Momentum (PDF)
• The YouTube policy has changed (or will soon), so you may not be able to watch my videos.  As a test, try this link.  Then try this one and, finally, this one.  Hopefully the second one will continue to work after the change.  And the second one should have the added benefit of no required ads.
• Collision Lab (instead of the one in the handout).  Find a way to set up and record data for four different types of collisions between a dynamics cart and a "wall" -- all with the same closing speed.  Enter data into a copy of this spreadsheet and enter formulas to perform the required calculations. 
  • The four collisions should have the same closing speeds, but they should vary according to these characteristics...
    1. High e, low F
    2. High e, high F
    3. Low e, low F
    4. Low e, high F
  • Basic Lab setup:
  • Graphical Analysis (PWA version) Link
  • Directions:
    • Open the graphical analysis app and connect your cart.
    • Set up your screen with a force graph and a velocity graph.
    • Change your sampling rate to 500 samples per second
    • Figure out how to create the four types of collisions, listed above.  Choose one of them to do first.  Record data during the collision in your spreadsheet.
      • To find impulse (area under the curve), use the integral tool.
      • To find other things (max force, duration, etc.), the statistics tool is helpful.
      • Use the balance to find your cart's mass.  This may change if you modify your cart.
    • For all four collisions, keep the impact speed as constant as possible.  This means that you will have to adjust your release point if you modify the collision area.

Homework:

• p. 13 -- Multiple Choice:  Here are the answers...  

Class 53.5:

Warm Up:  A sled-pulling machine accelerated a 68kg student from rest to 11.7m/s over a distance of 14.7m, and in a time of 2.36s.  The sled's mass was 6kg.  The students powering the machine pulled over a distance of approximately 3m.

1.  What was the acceleration?  At that rate, how long would it take to go from "0-60" in mph?

2.   What was the machine's output energy?

3.  What was the machine's power output, in Watts and Horsepower?

4.  What is the conversion from horsepower to studentpower?

5.  What average force did each student apply?

6.  What was the machine's input energy?

7.  What was the machine's efficiency?

8.  What protocol could be used in the future to make sure that no one flies too far?

Today:

• Just the warm-up

Homework:

• None.  Enjoy your break!

Class 53:

Warm Up:  Suppose I place some foam on my table top, and then I shoot it with the two darts in the picture, using the same Nerf ^® gun.  Compare the effects of the two darts impact on the motion of the foam.

Today:

• Return retakes -- be aware that not everyone has taken it yet.
• Check/review homework
• Launch some human projectiles
  • The jump contour (vs. initial speeds of 8-12m/s)  
  • A1/2 Sled Jump Videos

Homework:

• None

Warm Up:  Collect velocity data, so we can estimate speeds later on.

Today:

• Launch students and record video for determining velocities.

Homework:

• If everything went well today, bring snow shovels tomorrow

Warm Up:  None

Today:

• Optional test retake
• Sled accelerator progress: 
  • Old one
  • New one
• Old ones
  • Roof
  • Barn

Homework:

• Bring warm/snow clothes tomorrow -- hat, gloves, boots.  Bring a helmet if you want to ride.
• Homework that was due yesterday is now due on Thursday.

Class 51:

Warm Up:  

Today:

• Check/review homework 
• Notes:  Elastic/Inelastic collisions and Coefficient of Restitution (p.3-4)
  • Notes key  Video from A5/6 Today
• Knots?

Homework:

• Problems 10 and 13-15 on pages 8-10

  • Problem solutions

  • New solutions to #14-15

Class 50:

Warm Up:  

Today:

• Unit 7 Handout: Momentum (PDF)
• Notes:  Momentum, Impulse, and conservation of momentum (p.1-3) Video from today's A5/6 class
  • Notes key
• Knots?

Homework:

• Problems 1-3 and 5-9 on packet p. 7-8.   Answers are at the bottom of page 10.

  • Problem solutions updated

  • Video explaining problems 1-6

  • Homework help video for problems 7-10

Class 49.5:

Warm Up:   A ball rolls down a 2m tall hill in a vacuum, flying off the hill in a horizontal direction and traveling another 3.38m horizontally before hitting the ground, 2m further below.  As the ball rolls down the hill, there is static friction between the ball and the hill, but there is no air resistance during this event. 

1. How would you use energy conservation to find the speed of the ball at the point where it flies off the ledge?

2. How would you use projectile motion strategies to find the speed of the ball at the point where it flies off the ledge.

3.  Why would the two calculated speeds be different?  Which one would be correct? 

4.  Static friction does not reduce the mechanical energy of the ball, but it is an important part of this problem. 

     a.  Why does static friction not do non-conservative work on the ball, converting energy to heat? 

     b.  Why is static friction an important part of this problem?

5.  Something totally different -- mechanical energy is conserved in the system analyzed above.  What object(s) are part of the system?  Is there a problem with this?  Spreadsheet -- where's PE going when a ball falls

Today:

• Return tests -- optional retake next Tuesday
• Preview of next unit  Unit 7 Handout: Momentum (PDF)
• Tie knots

Homework:

• None

Warm Up: 

Today:  Test

Homework:

• None

Class 48.5:

Warm Up: 

Today:  Test review (knot tying on Tuesday)

• Test
  • Formulas
  • Format:
    • 13 Multiple choice -- various concepts
    • 6 Problems
      • Work by a force in the direction of the displacement
      • Work by a force not in the direction of the displacement
      • Power, Kinetic Energy, and Speed
      • Conservation of Energy with both types of potential energy and non-conservative work -- plus efficiency
      • Conservation of energy without non-conservative work
      • Roller Coaster problem with multiple parts -- frictionless parts with no W_NC; parts with W_NC; changes in height, speed etc.; and a spring.
  • A few tricky concepts:
    • Calculating work done by a variable force
    • Visualizing changes in motion, position, and energy (like the graphing at the beginning of the packet)
    • Understanding when mechanical energy is and is not conserved, and the implications
    • ways to find k
  • The big idea:  PE_S0 + PE_G0 + KE₀ + W_NC = PE_S + PE_G + KE
• "4 minute drill" on p. 20 -- #4 won't be on it. Unit 6 Handout (PDF) Unit 6 Answer Key
• Energy Conservation Practice Drill, p. 20 -- video from class

Homework:

• If you want more practice with energy conservation, write the simplest possible equations for the energy scenarios situations PDF.  Here are my equations.  The thing that makes them the simplest is that quantities that change are assumed to be zero on one side of the equation.

Class 47.5:

Warm Up: 

1.  How does a hydraulic lift facilitate work with a small input force and a large output force?  In general, how do hydraulics produce so much force?
2.  How could you lift a room full of people by blowing air through a straw?

Today:

• A1/2 --Notes: #8-9 on p. 12
• Trucker's hitch challenge clarifications --  (for 2% on Monday's test) -- tie a Trucker's hitch as shown in my videos, explain the physics, and remove it. Here are some details.
  • Requirements:
    • You must tie the hitch in under 2 minutes. 
    • After tying, tension measured by the scale must be at least 50N.
    • While the hitch is tied, you must use physics (correctly) to explain why this hitch achieves such high tensions (if you don't do just this part, you get 1%).
    • You must untie and remove the hitch in under 45 seconds.
  • Plus one more percent for the highest tension achieved (out of all physics 200 students) -- but only if you meet the other requirements.
  • *You may use more than one slippery half hitch if you want.
  • Trucker's Hitch Videos:
    • How to tie all of the knots
    • Quick run-through with minimal instructions
    • Physics Explanation of Trucker's Hitch -- two options
    • Trick for increasing your force

Homework:

• Prepare for the Trucker's Hitch Challenge, tomorrow.
• Test on Monday

Class 47:

Warm Up: 

Today:

• Check/review homework -- sorry I skipped kWh in the notes.  I forgot it was part of the practice test.
• A5/6 --Notes: #8-9 on p. 12
• Trucker's Hitch Videos:
  • How to tie all of the knots
  • Quick run-through with minimal instructions
  • Physics Explanation of Trucker's Hitch -- two options
  • Trick for increasing your force

Homework:

• Trucker's Hitch testing on Friday -- prepare
• Optional Practice  -- Problems from Energy Scenarios and Problems PDF Solutions
• Test Next Monday

Class 46.5:

Warm Up: 

Today:

• Awards presentation
• Check/review homework

Homework:

• Mr. Pennington's Practice Test -- problems section -- p.18-19 Unit 6 Answer Key
• Test on Thursday

Class 46:

Warm Up:  None

Today:

• Skip the homework check.
• Egg bungee contest -- collect fresh data and compete.
• Work time
• Unit 6 Handout (PDF)

Homework:

• Mr. Pennington's Practice Test, multiple choice only -- p.15-17 Unit 6 Answer Key
• Finish the previous (class 45.5) homework if you didn't do it.

Class 45.5:

Warm Up:  Loop-The-Loop Revisited

A big part of the video focuses on their calculations of the minimum entry speed and the g-force experienced by the driver at the bottom.  If he's going too slow, he will fall off at the top.  If he's going too fast, he will black out from the g-force at the bottom.  They finally calculate 16.1m/s to be the right speed for a 40ft tall loop -- with a normal force of 6g at the bottom.  [**They assume that mechanical energy is conserved!!]

Given the other constraints of this problem, how would changing the radius affect the g-force felt at the bottom of the loop?  What if the radius were increased?  What if it were decreased? Solution

Today:

• Check/review homework.
• Continue Egg Bungee Lab --
  • collect force data and make a prediction. Predict what mass will stop at a height of 5cm if you drop it from 10cm below ceiling height.  You may drop this mass from this height more than once, but you are not allowed to test other masses.
  • Modify your measuring process and model, if necessary, before tomorrow's egg bungee drop.

Homework:

• #2 of Practice quiz (p. 10)
• Unit 6 Answer Key

Class 45:

Warm Up:  A spring is hanging from the ceiling.  A 500g mass is hooked onto the spring without initially stretching the spring, as shown, and released from rest.  Ater bobbing for a long time, the mass comes to rest 37cm below its release point.

1.  What would a graph of energy vs. time look like, during the first full bob down and back up? Include all forms of mechanical energy.  For simplicity, ignore non-conservative work and OE.graph -- without OE

2. Stop assuming 100% efficiency, because the apparatus clearly isn't 100% efficient.  During this process (release to rest), how much mechanical energy is converted to OE?

Today:

• Check/review homework
• Egg Bungee Lab Preparation -- set up a spreadsheet to perform calculations.  Video explaining how to set up the spreadsheet -- and how the contest works

Homework:

• Practice quiz, p. 9, #1 only
•  Unit 6 Answer Key

Class 44.5:

Warm Up: 

For an ideal spring, the applied force is directly proportional to the stretch distance.

The spring constant, k, is a ratio of force to stretch^* distance.  The units we will use for k are N/m. 

Suppose a screen door spring has a spring constant k = 40N/m.

1.  What is the tension in the spring when it is stretched 1m?

2.  What is the tension in the spring when it is stretched 20cm?

3.  How much work is required to stretch the spring from a stretch distance of 0m to a stretch distance of 1m?

_{*In the case of a compression spring, x is the compression distance.}

Today:

• Note -- If you turned in the lab by 7/8 yesterday, I graded your work and gave you feedback.
• Check/review homework and Atwood Machine Lab
• Notes: Springs + Odds and Ends -- Unit 6 Handout (PDF)  Unit 6 Answer Key  Video from A5/6 -- Springs, etc.

Homework:

• p.13 1-3  Video explanations  Unit 6 Answer Key

Class 44:

Warm Up:  Consider the event you examined -- which begins as heavier block A starts to fall, causing a lighter block B to rise -- and which ends just before block A hits the table. 

1.  Populate graph on the right with bars showing the distribution of energy at the beginning and the end of this event.

2.  How does non-conservative work fit into this model?

Today:

• Check/review homework
• Notes:  Fix Calories (p.7) and Efficiency (p.12) -- Joule's Apparatus Unit 6 Handout (PDF)  Unit 6 Answer Key  Video from A5/6 -- Calories and Efficiency
• Atwood Machine Energy Analysis Lab -- Complete parts 1 and 2 of the calculations and turn in to Google Classroom.  Change of plans -- you must turn in your own unique spreadsheet.  You can help one another, but turn in your own, unshared spreadsheet.

Homework:

• P.7-8, work and energy practice problems 1-5. 
• Answers:  1a. 40J  1b. 400W  1c. 21.7m/s  2a. 161,040J  2b. 0.49 Snickers Bars  3a.17.8N   3b. 535J   3c.17.7m/s   4. 0.67hp   5a. 604,747J   5b. 201,582W   5c. 270hp   5d. 43.8   5f. 65.7m
• Unit 6 Answer Key 

Class 43.5:

Warm Up: 

Today:

• Unit 6 Handout (PDF)  Unit 6 Answer Key
• Collect data for the Atwood Machine Energy Analysis Lab.  Set it up like this.

Homework:

• Finish the practice problems on p. 6-7 (#4-7 and #7-11).  Ignore the headings; the problems are mixed up. Unit 6 Answer Key

Class 43:

Warm Up: 

1. What will this energy vs. time graph look like?

2. What will it look like with friction?

Today:

• Check/review homework
• Unit 6 Handout (PDF)  Unit 6 Answer Key
• Finish notes through #3 on page 6.  Video from A5/6 -- Energy Intro Part 3
• Work on roller coaster problem -- #6 on page 8.

Homework:

• Finish the roller coaster problem (#6, page 8) -- if it wasn't finished in class.

Class 42.5:

Warm Up:  How can you make the PhET skate boarder do a continuous, clockwise loop-the-loop?

Today:

• Unit 6 Handout (PDF)  Unit 6 Answer Key
• Work our way through the Work and Energy notes. Video from A5/6 -- Energy Intro Part 2

Homework:

• Graphical Energy Conservation Practice -- sheet handed out in class. (PDF) Answers to energy graphing practice

Class 42:

Warm Up:  The apparatus on the right is called an Atwood Machine.  Assume that the pulleys and strings are massless and frictionless, and that the masses start at rest.

1.  What kind(s) of energy does each mass have in the beginning?

2.  How does the energy of each mass change?

3.  What kind(s) of energy will each mass have just before the 2kg mass hits the surface?

4.  What will happen to the overall energy of the system?

Today:

• Midterm score distribution
• Take a look at the exams and check for grading mistakes.
• Preview the rest of the year, and let me know if you have any particular interests.  This is the last year for this course.
• Unit 6 Handout (PDF)  Unit 6 Answer Key
• Work our way through the Work and Energy notes. Video from A5/6 -- Energy Intro Part 1

Homework:

• None