Totoro catching a full wave (going from peak to peak) every 4 seconds.  Courtesy of Lina Hang. Class 60 Friday, 5/7/21

Warm Up:  

The frequency of a wave describes number crests or troughs that pass a particular point in a given amount of time (a.k.a. cycles per second).  The units are Hertz (Hz).

1.  What is the frequency of the wave pattern on the right?

2.  If the distance between two successive crests (i.e. wavelength) is 4m, what is the speed of the waves on the right?

3.  What is the formula for wave speed, in terms of frequency and wavelength?

4.  What's unrealistic about the bobbing cat GIF?

 

Today:  

 

 

Homework:

Class 59 Thursday, 5/6/21

Warm Up:  None

 

Today:    Test -- Remote and Blue, join the Google Meet

 

Homework:

  • None

Class 58 Wednesday, 5/5/21

Warm Up:  None

 

Today:   Optional -- test review session

 

Homework:

  • Study for test on Thursday (Blue, Gold, and Remote)

Class 57 Tuesday, 5/4/21

Warm Up:  

1. What is a spark? Breakdown voltages,

2.  How does a jacob's ladder work?  How is it used as a safety device?

spark gap

 

Today:  

Homework:

  • Study for test on Thursday (Blue, Gold, and Remote)

Image result for bird on a power lineClass 56 Monday, 5/3/21

Warm Up:  

1.  Why doesn't a bird on an uninsulated power line get shocked?

2.  Would a bird get shocked if it landed on a Van de Graaff generator?

 

Today:  

  • Review the homework:  18.7  Solutions  18.8 solutions

  • In class, do the Van de Graaff demonstrations from last class.

  • In class? -- do the multiple choice section of Mr. Pennington's test (packet p. 21-23).  Then go over the answers.

Homework:

 

Class 55 Friday, 4/30/21

Warm Up:  

1.  Have you ever seen a Van de Graaff generator that did not have a spherical (or hemispherical) dome?

2.  Diagram C shows two conductors with excess positive charges.  Why do the excess charges reside on the conductors' surfaces?  Why are the charges closer together near the pointy part of the rightmost conductor?  What implications does this have for Van de Graaff generator design?

Today:  

Homework:

 

 

Class 54 Thursday, 4/29/21

Warm Up:   A "pith ball" is hanging next to the dome of a Van de Graaff generator.  The pith ball is filled with foam, and it is coated with a conductive paint.  Predict and then explain the behavior of a "pith ball" hanging near the Van de Graaff generator.

1.  What will happen to the pith ball when the VDG is turned on?

2.  What will happen to the pith ball when the dome of the VDG (still running) is grounded?

3.  What will happen to the pith ball when the pith ball is grounded (while the VDG continues to run)?

4.  Why?

Today:  

Homework:  

Class 53 Wednesday, 4/28/21

Warm Up: 

How does a Van de Graaff Generator Work?

MIT video -- inducing dipoles with a VDG

Another video about how a VDG works

 

Today:  

Homework:  

Class 52 Tuesday, 4/27/21

Warm Up:  

The electrophorus is charged by rubbing a cat(fur) against the top of an insulating plate (I).  Then the conducting plate (C) is placed on top of the insulating plate and is touched by the physicist.  Assuming that the cat fur has a strong affinity for positive charge...

1.  What is the charge of the plate after it is touched by the scientist? 

2.  Explain how the conducting plate becomes charged.

3.  What is the ground in this demonstration?

Today:  

Homework:  

Class 51 Monday, 4/26/21

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?

3.  What events contributed to this gas station fire?

Today:  

Homework:  

 

Class 50 Thursday, 4/15/21

Warm Up:   Test retake today.  No warm-up.

Today:  

Homework:  Have a great Spring Break!

 

Class 49 Thursday, 4/15/21

No class or meet.  If you're retaking the test, prepare for the retake tomorrow.

Class 48 Wednesday, 4/14/21

Google Meet -- The topic is the test and the test retake.

 

Class 47 Tuesday, 4/13/21

No class or meet.  Check your email for your test and solutions links.  If you're retaking the test, prepare for the retake on Friday.

Class 46 Monday, 4/12/21

Warm Up:   Test today.  No warm-up.

Today:  

  • Test for everyone.
  • Fill out the String Instrument Project Survey

Homework:  None.

Image result for quadcopter controlsClass 45 Friday, 4/9/21

Warm Up:   A quadcopter has four propellers that usually alternate in their directions of rotation.

  1.  How does conservation of angular momentum enable this quadcopter to achieve a yaw
  2.  In order to pitch or roll, why can't one motor just speed up (without the opposite motor slowing down)?

Today:  

  • Review the homework
  • Test Review
  • Test Format:
    • 15 Multiple Choice (1 point each) -- study the notes
    • 5 problems (30 points total)
      • Apply various angular kinematics formulas
      • Convert between angular and linear units
      • Torque
      • Rotational Version of Newton's 2nd Law
      • Angular Momentum
      • Conservation of Angular Momentum
      • Conservation of Energy with rotational and translational energy
      • Torque balancing by locating a fulcrum

Homework:  Prepare for the test on Monday (all students -- Blue in person, Gold and Remote via Google Meet)

Image result for dry limbs firewood driftwoodClass 44 Thursday, 4/8/21

Warm Up:  

Suppose you need to 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:  

  • How can we find the weight of a meter stick using only a 200g hooked mass?
  • Review the homework

Homework:  

Complete the problem section of Rotational Motion Practice Test # 2, Rotational Motion  Solutions to Rotational Motion Practice Test #2.  If you don't understand the solutions, watch the videos below. 
Class 43 Wednesday, 4/7/21

Warm Up:  

Suppose you need to remove exactly three squares of toilet paper from the roll shown in the picture, and one of your hands is unavailable.

1.  What strategy might you use to tear off exactly three squares?

2.  Why would this task be easier with a nearly-full roll?

3.  The custodians at Burlington High used to remove the rolls when they were almost empty, because it became nearly impossible to pull off more than one square at a time.  Can you guess why? Hint: at BHS, the toilet paper fit more tightly on the dispenser axle.

Today:  

  • Review the homework from yesterday.

Homework:  

Complete the multiple choice section of Rotational Motion Practice Test # 2, Rotational Motion  Solutions (# 8 is wrong -- should be D) to Rotational Motion Practice Test #2.  If you don't understand the solutions, watch the videos below. 
Image result for compound bow drawnClass 42 Tuesday, 4/6/21

Warm Up:  

1.  Where does a compound bow store most of its energy?

2.  What purpose(s) do the pulleys of a compound bow serve?

Today:  

  • Review the homework from Friday.
  • Extra Credit Real World Problem (begin it together) -- Find the moment of inertia of some wheels an their axle by accelerating them with a weight and a wrapped string.
    • Axle diameter = 5/16", Mass of falling weight = .154kg, String Length = 84.5cm, Acceleration time = 9.93s, Deceleration time = 3.25s.
  • Work on the problem section of Mr. Pennington's practice test.

Homework:  Complete the problem section (p.21) of Rotational Motion Test Review #1  Solutions to Pennington Test Review Problem solution video

Class 41 Monday, 4/5/21

Warm Up:   Test retake day -- Momentum & Impulse

Today:  

  • No Meet

Homework:  See last class.

Class 40 Friday, 4/2/21

Warm Up:  

Falling cats continued...

1.  Can we simulate what this cat does on a lazy Susan?

2.  We have already agreed that you can't pick yourself up by your bootstraps.  This video implies that you can turn yourself around by your boot straps (or maybe by a belt loop).  Is this true?

 

Today:  

Homework:  This will all be due on Tuesday, since the retake is Monday.  There will be no new work assigned on Monday.

Class 39 Thursday, 4/1/21

Warm Up:  

  1.   How do falling cats always manage to land on their feet?
  2.   Why do falling people flail their arms around?

Watch the first part of the video on the right.  Watch the rest tomorrow.

Today:  

Homework:  

Class 38 Wednesday, 3/31/21

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.

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:  

Homework:  

Class 37 Tuesday, 3/30/21

Warm Up:  

1.  Suppose you need to screw an abutment into a fixture that is implanted in someone's jaw.  How can you make sure that you screw it in just tight enough, but not too tight?

2.  Assuming that the 100N bar on the right has evenly distributed mass, where (approximately) should a fulcrum be placed in order to achieve zero net torque acting on the bar?

Today:  

  • Go over the test answers and grading.  Don't forget that retakes are Monday.  Make sure you show up if you want to take the retake.  If you have a legitimate reason for being absent on Monday, let me know as soon as you can.
  • Review the homework
  • .
  • Notes: Rotational Kinematics

Homework:  Chapt 10.2 -- Kinematics of Rotation Practice (p.10) -- Key

Class 36 Monday, 3/29/21

Warm Up:  

In the rotational (angular) motion unit, we will be using new units that are analogous to our current, linear units.  You will need to be able to work in radians.

1.  360º = _____ radians

2.  90º = _____ radians

3.  2 radians = _____ degrees

Today:  

  • Return tests -- Retake will be next Monday.
  • Review the homework -- do a torque-balancing problem with the fulcrum in the wrong place
  • Notes: Angular Acceleration and Intro to Rotational Kinematics (p.7)  Notes key  Video from last year's class

Homework:  Angular Acceleration Practice (p. 8) -- Key

Class 35 Friday, 3/26/21

Warm Up:   None -- test today

Today:  

  • Unit 7 Test for everyone (Gold, Blue, and Remote)

Homework:  Torque Practice (packet p. 4-7)   Torque Practice Solutions

 


Class 34 Thursday, 3/25/21

Warm Up:   Consider a system comprising a ball and the Earth.  They are held apart by a distance (x) and then released, and the ball falls to the Earth and hits it.  Of course, the Earth also moves a very small distance toward the ball.  This is repeated with a variety of balls of the same mass (m) and radius (r), separated from the Earth by the same distance (x).  Assume that there is no air resistance.

1.  Describe some types of balls that would produce the highest and lowest impact forces when they collide with the Earth.  Explain how these balls' characteristics will affect impact force.

2.  Describe some types of balls that would experience the largest and smallest changes in momentum during their collisions with the Earth.  Explain how these balls' characteristics will affect impulse.

3.  Describe the types of balls that will produce the highest and lowest impulse during their collisions with the Earth.  Explain how these balls' characteristics will affect impulse.

4.  Go back to number 1 and make sure that your answers were as specific as possible.

5. Compare the Earth's experience to the Ball's experience, in terms of...

  • Impact force
  • Impact time
  • Impulse
  • Change in momentum

6. Visualize a graph of momentum vs time for this entire system.

 

Today:  

  • Test review -- discuss the homework and the optional homework.
  • Information about tomorrow's test: 

 

Homework:  Get ready for the test -- the test will be tomorrow for everyone.


Class 33 Wednesday, 3/24/21

Warm Up:  

Suppose I stand a board on end and shoot it with a Nerf ® dart. 

1.  Am I more likely to knock the board over if I use a dart that sticks to the board or if I use a dart that bounces off of the board?  Why?

2.  Which experiences a greater impulse, the dart or the board?  Or do they experience the same impulse?

 

Today:  

  • Discuss the homework from last night, plus the lab from Monday.
  • Complete the multiple choice section of the 2017-2018 Momentum and Impulse Test (packet p.13)

Homework:  

Class 32 Tuesday, 3/23/21

Warm Up:   None.  Unit 6 Test retake day

Today: 

  • Blue people -- pick up your Unit 8 Packets.
  • Test retakes for Blue, Gold, and Remote
  • If you're not working on the test retake, begin the homework.

Homework:  Complete the problems section of the 2017-2018 Momentum and Impulse Test (packet p.14-15).  Solutions

Class 31 Monday, 3/22/21

Warm Up:  

How does a helmet protect one's head from the force of an impact?

Today: 

  • Discuss the homework.
  • Collisions Lab:
    • Introduction
    • In small groups, see if students can find a way to calculate coefficient of restitution.  Try to solve this example problem... a ball that is dropped from a height of 60cm rebounds to a height of 40cm.  What is the coefficient of restitution for this collision between the ball and the floor?
    • Watch the three short videos below and then use the data to complete the table and questions in the packet (packet p. 11-12) (Unit 7 Packet)

Homework:  

  • Tomorrow:  Test retake for everyone -- Gold will do it virtually

  • Finish the collisions lab by Tomorrow evening.  Then check your answers by watching this video discussion .  If you have questions, ask them on Wednesday.


Friday, 3/19/21 -- No School.  Parent-Teacher Conferences
Class 30 Thursday, 3/18/21

Warm Up:  

A potato launcher uses compressed air to push a chunk of potato out of a pvc tube ("barrel").  The air, which is compressed to 40psi, can be quickly released by pulling the trigger. 

1.  Will the potato reach a higher velocity if it is inserted at point A or at point B?

2.  Will the potato reach a higher velocity if a 0.5m long barrel is used, or if a 1.5m long barrel is used?

3.  Explain your answers in terms of momentum and/or impulse.

Today: 

Homework:  Complete #16-18 (conceptual questions and ballistic pendulum) on packet p.10. Problems Key  If you have questions, watch the solutions video.

Class 29 Wednesday, 3/17/21

Warm Up:  

1.  When one Newton Cradle ball hits another, the first ball stops and one other ball starts moving at the first ball's initial velocity.  Why don't two balls begin moving half as fast as the first one?  Or three balls at 1/3 the original speed?  Wouldn't momentum be conserved in any of these ways?

Today: 

  • Discuss Homework
  • Notes on Elastic/Inelastic Collisions and Coefficients of Restitution (packet p. 3-4)  (Unit 7 Packet) Notes key (In the notes key, I made some mistakes on #22 -- coefficient of restitution example -- I believe the answer is correct, but the variables are mislabeled confusingly.)

Homework:  Complete 13-15 of "Elastic/Inelastic Collision Problems..." on packet p. 9-10. Problems Key

Class 28 Tuesday, 3/16/21

Warm Up:  

1.  What will happen if I hold a tennis ball on top of a basketball and drop them to the floor together?

2.  What if I reverse their positions?

3.  Why does this happen?

 

4.  Which version of the impulse formula (on the right) do you think is more useful?  Why?

 

Today: 

  • Return tests and discuss the grading
  • Important dates:  Put these dates in your calendar and don't schedule other appointments for these times (if they apply to you).  You are expected to take tests on time unless your reason for not taking the test is worthy of an excused absence.
    • Tuesday, 3/23 -- Retakes for Everyone (Blue, Gold (remotely), and Remote).
    • Friday, 3/26 -- Unit 7 Test for Everyone (Gold, Blue (remotely), and Remote).
  • Discuss the homework.
  • Notes on conservation of Momentum (packet p. 3)  (Unit 7 Packet) Notes key
  • Do a few simple example problems

Homework:  Complete 7-12 of "Conservation of Momentum -- Basic Problems" on packet p. 8. Problems Key   Homework help video

Class 27 Monday, 3/15/21

Warm Up:   None.

Today: 

  • No Meet
  • Present donuts
  • Unit 6 Test

Homework:  Nothing new.  See Google Classroom for the most recent assignment.  It's due tomorrow.

Class 26 Friday, 3/12/21

Warm Up:   None.

Today: 

  • No Meet
  • Present donuts
  • Test

Homework:  

Class 25 Thursday, 3/11/21

Warm Up:   None. Instead, let's take a brief moment for questions about tomorrow's test.

Today: 

Homework:  

Class 24 Wednesday, 3/10/21

Warm Up:  

1.  A lightweight object and a very heavy object are sliding with equal speeds along a

level frictionless surface. They both slide up the same frictionless hill.

Which rises to a greater height?

       A) The lightweight object, because it weighs less.

       B) They both slide to the same height.

       C) The heavy object, because it has greater kinetic energy.

       D) Cannot be determined from the information given.

2.  A car and a truck driving on snow with the same speed and tires with the same

coefficient of kinetic friction both lock their tires and skid to a stop.  If the truck has 2x the

mass of the car, how do their sliding distances compare?

       A) The car slides farther.

       B) The truck slides farther.

       C)  Their sliding distance is equal.

       D)  Cannot be determined from the information given.

Today: 

  • Discuss the homework
  • Test Review
    • Format:
      • 12 Multiple Choice
      • 6 Problems -- 14 parts in all
      • Problems relating to...
        • Simple work formula
        • Work done by a force in a different direction, relative to movement
        • Work-Energy Theorem
        • Power
        • KE formula
        • PE formula (gravitational)
        • kWh (kiloWatt-hours) and energy cost
        • Conservation of Energy (with and without non-conservative work)
        • Spring force
        • Spring PE
        • Roller coaster problem with multiple parts -- partly with friction, partly without friction, one spring included
        • Nothing about efficiency
    • Drill and Practice Excercise (p. 18 of the packet -- Unit 6 Packet -- Work and Energy)

Homework:  

  • No homework

  • Blue and Remote -- Test on Monday

  • Gold -- test on Friday

Class 23 Tuesday, 3/9/21

Warm Up:  

1. When you collect force and stretch distance data, is it better to remove the weights between each measurement, or should you leave the weights hanging on the bungee throughout the entire measurement process? 

2.  Given these two options, if you chose the less sensible procedure, is it likely that your final estimate of the egg's low point would be too low, or would it likely be too high?  Explain.

 

 

Today: 

Egg Bungee Jump Challenge:  Directions and data sheet pdf

Homework:  Complete the remaining problems (we already did #4) from Pennington 2015-2016 test (packet p. 11-15).  Solutions.

 

Class 22 Monday, 3/8/21

Warm Up:  

1.  When does each of these energy conservation equations apply to the diagram below?

2.  Would your answer change if this were a completely frictionless environment?

 

This Week and Next:

  • Monday -- bungee jumping spreadsheets

  • Tuesday -- Blue Egg Bungee Jump Contest.  "Groups" of 1-3 students pursue a bungee jump where a weighted egg (weight TBD) comes closest to a ceramic tile without breaking.  You get two tries.  You specify a conservative tile height (first drop) and a risky tile surface height.  Both heights must be determined before the first drop.  The prize is donuts (or the gluten-free equivalent).  Remote students are excused, but you are welcome to team up with students in class if you want.

  • Wednesday -- Test review

  • Thursday -- Gold bungee jump contest.  Same details as Blue group (see Tuesday).

  • Monday -- Blue test

 

Today: 

 

Homework: 

 Finish the spreadsheet (above)

 

 

Class 21 Friday, 3/5/21

Warm Up:  

A  piece of elastic hangs from the ceiling.  A weight is attached to the end of the elastic and released.  The weight falls and bobs back up through two cycles.

1.  Sketch a graph of energy vs time for this event if we assume that mechanical energy is conservedd.  On your graph, include separate curves for PEgravitational, PEspring, KE, and Total E.

2.  How would the graph look different if internal friction and "other energy" were included?

Excel graph

 

Today: 

Homework:

  • Complete bungee problem #2 -- packet p. 17.

Class 20 Tbursday, 3/4/21

Warm Up:   None -- to save time for test retakes

Today: 

  • Briefly discuss the homework -- especially #3.
  • Gold and Remote opportunity for test retake.

Homework:

  • Watch this video and finish the notes on packet p. 8 ("other energy," electrical energy, and efficiency) Notes key 

  • Complete Multiple choice (1-16) and Problem #4 from Pennington 2015-2016 test (packet p. 11-15).  Solutions.  Note -- I think the real answers to #5 and 6 are not the same as the expected answers to #5 and 6.  See if you can figure out what's wrong with those multiple choice questions.

Class 19 Wednesday, 3/3/21

Warm Up:   Bonus question due on Friday (email or on paper) -- Assuming that mechanical energy is conserved, at precisely what minimum speed must a car enter a 10m radius loop-the-loop in order to not lose contact with the road surface?

Today: 

Homework:

  • "More Work and Energy Practice Problems" #1