Class 49.5: Friday, 2/9/24

Warm Up: 

1.  What is the point of having a variety of gears on a bicycle? (or a car, motorcycle, etc.)

2.  If you ride as fast as possible in one gear, how does your acceleration change over time?

3.  How does changing to a higher gear affect F and d  (e.g. Fd vs Fd)...  where your foot meets the pedal; and where the tire meets the road?

4.  At what point should you change gears?

 

Today:

  • Check/review homework
  • Test review
    • The formulas -- 
      • What do the letters mean? 
      • What are the units? 
      • What is the purpose of each formula?
      • Be ready to solve for any part
    • Definitions:  Work, Power, Energy, PE, KE, OE, WNC, Efficiency
    • Calculate work done by a variable force.
    • Know what information is necessary, and which information isn't (don't be distracted by extra information).
    • Know how to apply the key formula (energy changes with work), and how it relates to OE.
  • If you want some extra practice, write the simplest possible equations for the energy video 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.

Homework:

  • Prepare for test on Monday
Image result for compound bow drawnClass 49: Thursday, 2/8/24

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?

3.  Based on this simplified graph of draw force vs distance, how much work is done in fully drawing the bow?

 

Today:

Homework:

Class 48.5: Wednesday, 2/7/24

Warm Up: 

None

 

Today:

Homework:

  • None
Class 48: Tuesday, 2/6/24

Warm Up: 

Assuming that all three bows are drawn to a distance of 0.5m...

1.  Which bow stores the most energy when it is drawn to this distance?

2.  Estimate the energy stored in each bow.

3.  Why is the compound bow curve so different?

 

Today:

Homework:

  • None
Class 47.5: Monday, 2/5/24

Warm Up: 

1.  Can you guess what the "sisyphus train" does?

2.  How did it get that nickname?

Today:

  • Check/review homework
  • Work time

Homework:

Class 47: Friday, 2/2/24

Warm Up:  Sketch a line graph showing the changes in energy from the point when the mass is released until bobs back up to its highest point.  Include PEgrav, PEspring, KE, and OE.

graph -- without OE

Today:

  • Check/review homework
  • Go over the lab answers.  If you turned in your lab on time, I pasted my calculations (based on your data) into a black-outlined box in your spreadsheet.  If your speeds were wrong, I used your wrong speeds for my calculations.  Here's a video explaining my calulations.
  • Electrical energy units won't be on this test, but they're on Mr. P's old test, so let's go over them (handout p.11)

Homework:

Class 46.5: Thursday, 2/1/24

Warm Up:  Consider the event you examined in the pulley lab -- 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 "ground." 

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

Today:

  • Check/review homework
  • A7/8  -- a bit more work time on lab
  • Turn in your lab, if you haven't already -- we will go over it tomorrow
  • Springs Notes -- p. 11.  Unit 6 Handout (PDF)  Notes key

Homework:

  • Bungee Drop Problem (not in the handout):  A 0.5kg mass is attached to the lower end of a spring that is hanging from the ceiling.  The mass is held motionless and then released from the point at which the spring is just about to begin to stretch.  The mass drops to some low point, bounces back up, and continues to bounce for a long time.  After the mass finally comes to rest, the spring is stretched a distance of 0.37m.
    • Find the spring constant (k) of the spring.
    • Calculate the potential energy stored in the spring after the mass is finished bouncing.
    • Calculate the distance between the release point (zero stretch) and the lowest point reached by the end of the spring during this scenario.
Image result for wedge mechanical advantageImage result for hockey stick fulcrumImage result for boat winchClass 45.5: Tuesday, 1/30/24

Warm Up: 

The pictures on the right all show simple machines.  Simple machines allow the same work to be done with more convenient combinations of force and distance. 

1.  For each picture, identify the machine (s).

2.  For each machine, tell how the machine alters the distance over which force must be applied by the human using the machine.

3.  How does the machine alter the force that the human must apply?

4.  Which "machine" is fundamentally different? Why?  If you don't have a quick answer to this, move on to the other questions and come back to this one.

Today:

  • Check/review homework
  • Finish Lab -- Turn-in via Google Classroom.

Homework:

Class 45: Monday, 1/29/24

Warm Up: 

A compact car (1,500kg) and a fully-loaded dump truck (36,000kg) are traveling at the same speed on level ground...

1.  Compare the distances that they will slide if they both lock up their wheels and skid to a stop.  Assume that their coefficients of friction are equal.

2.  Compare the distances that they will travel up a "runaway truck ramp" before coming to a stop. 

 

Today:

Homework:

Class 44.5: Friday, 1/26/24

Warm Up:  In this video, a driver supposedly enters a loop-the-loop at a speed of 36mph (16.1m/s).  The driver supposedly experiences 6g at the bottom and approximately 0g at the top. 

1.  They say the loop is 40feet high.  Based on that height, what is the approximate centripetal acceleration at 16.1m/s?

2.  Assuming that no non-conservative work is done once the car enters the loop, do these numbers really work?  If not, what numbers would?

Today:

  • Check/reveiw homework
  • Go over the Power formula on p. 5 and do the first  practice problem on p. 6. Unit 6 Handout (PDF)

Homework:

  • Finish the practice problems on p. 6-7.  Ignore the headings; the problems are mixed up.  Answers p. 6-7
  • Optional extra credit.  Solve part 1 of the warm-up.  Show all of your work.
Class 44: Thursday, 1/25/24

Warm Up:  A 1,000kg elevator travels upward a distance of 5m at a constant speed of 1m/s.

1.   What happens to the elevator's PE and KE during this trip?

2.   Use the formula PE0 + KE0 +WNC = PE + KE to write an expression for the non-conservative work done on the elevator.

3.   What is the net force acting on the elevator?  Use that net force to calculate the work done on the elevator.

4.   There should be a conflict between your answers to #2 and #3.  What is the conflict?  How can we resolve it?

Today:

Homework:

Class 43.5: Wednesday, 1/24/24

Warm Up:  Skip it.  Jump right to the notes.

Today:

Homework:

  • None
Class 43: Tuesday, 1/23/24

Warm Up:  Energy of the puck.  The puck sits on the ice...

1.   Which of these would change the puck's energy:  a) someone picks up the puck and holds it at a height of 1m; b) someone kicks the puck sideways, causing it to slide away  c) someone stands on the puck. 

2.  What is energy?

3.  Consider the person lifting the puck one meter and write an equation.  On one side of the equation, place the energy that the puck had before the action.  On the other side of the equation, place the energy that the puck had after the action.  Now find a way to balance the equation in a manner that makes sense.  Clearly, you're going to have to add a missing piece to make this work.

4.  Think about the missing piece you added to make the equation balance.  What are some ways that it could be varied without changing the starting and ending energy totals?

5.  Repeat steps 3 and 4 for the kicking of the puck (beginning before the kick and ending just after the puck leaves the foot).

6.  How can we wrap all of this into a tidy equation that sums up the most important aspects of this next unit?

Today:

Homework:

  • None
Class 42: Friday, 1/12/24

Warm Up:  A 100kg human stands at rest on a 25 degree slope.  The coefficient of friction between the human's shoes and the slope is 0.2.  The human suddenly runs downhill as fast as possible for 4m and then "slams on the brakes," sliding to a stop.

1.  How long does it take them to travel 4m?

2.  How far do they slide after hitting the brakes?

3.  Graph their motion for this event (consider downhill to be positive and uphill to be negative.

 

Today:

Homework:

  • Prepare for the midterm
Class 41.5: Thursday, 1/11/24

Warm Up: 

1. What's happening to this guy?  Why?  How does it work?

2.  In a moment I'm going to stand still; walk to the right at a constant speed; stop; and then walk to the left at a constant speed. Sketch graphs of my displacement, velocity, and acceleration.

Today:

Homework:

  • Prepare for the midterm
  • Optional -- prepare to retake some gravity/circles test problems tomorrow
Class 41: Wednesday, 1/10/24

Warm Up: Someone is using a leaf blower to propel a hovercraft on a hockey rink.  Assuming that this an essentially frictionless evironment, what can they do in order to travel in a uniform circle?  How does that work?

Today:

  • If you like your grade on the circles and gravity test, it can go on this quarter.  If you want to retake it, we will do that next quarter.  This way we can focus on midterm review.
  • B1/2 midterm?
  • Check/review homework
  • Get a copy of the "What's on the Exam?" document PDF.  You can also use your notes and old tests.  The exam is fairly comprehensive.

Homework:

  • Prepare for the midterm and generate questions if you have them.
  • Email me if you want particular types of problems for practice
Class 40.5: Tuesday, 1/9/24

Warm Up: 

1.  Is uniform circular motion a cause, an effect, or both?

2.  If it's a cause, what is its effect?  If it's an effect, what is its cause?

Today:

Homework:

Class 40: Monday, 1/8/24

Warm Up: None

Today:

  • Test
  • Midterm Review

Homework:

Class 39.5: Friday, 1/5/24

Warm Up: 

1.  Which formulas will be provided on the test?

2.  Which formulas can be easily derived?

3.  For each formula...

a) to what situation does it apply?

b) to what does each letter apply?

 

Today:

  • Test review -- drill and practice

Homework:

  • Prepare for Monday test
Class 39: Thursday, 1/4/24

Warm Up: Theoretically, any object in the Universe can be made to move in uniform circular motion.  Choose one of the random objects from the picture and describe what would you need to do in order to make that object move in uniform circular motion.

Today:

  • Practice Test PDF  Answers
    • Renumber it.
    • Note: On this practice test, there are 3 "non-planetary problems" and 4 "planetary problems."  Each problem represents a basic type of problem from this unit.  On tomorrow's test, there will be one fewer of each type of problem.  There will probably be one question about the relationship between Normal force and the perception of weight.
    • Complete 1-6. 
    • Go over the answers. 
  • Exam review -- will start in earnest on Monday.  For now, if you want to do some reviewing, just review your notes and past tests.  Or you can scroll down this page to review the year.

Homework:

  • Due on Monday -- Answer questions 7 and 8 (formerly #1 and #2, before we renumbered it) of the practice test. Practice Test PDF Answers
Class 38.5: Wednesday, 1/3/24

Warm Up: The graphic on the right is an attempt to illustrate the scope of circular motion problems that might appear on Friday's test.  Envision a problem scenario for each cause and condition.

Today:

  • Return retakes
  • Check/review homework
  • Tomorrow -- Circular Motion and Midterm review

Homework:

  • none
Class 38: Tuesday, 1/2/24

Warm Up: The car is driven at a constant speed through the loop-the-loop. 

1. Sketch a force diagram for each letter in the diagram.  Identify each force.

2.  Write an expression for normal force at each letter.

Today:

  • Look at the exam schedule -- exam details will be coming soon.  Check/review the homework
  • As a review, let's derive some formulas:
    • Fn: experienced by an object on the top (outside) of a vertical circle [we already did the inside, with the warm-up].
    • v: velocity of a satellite, based on orbited planet mass and orbital radius
    • g: based on orbited planet mass and orbital radius
    • v: velocity of a satellite, based on its orbital period (T)
    • T: an equation relating orbital period of a satellite, orbited planet mass, and orbital radius
  • Work on Practice Test #2 -- but cross off problem number 5.
  • Short test (1/2 block) on Friday over circular motion and gravity.  Retake next Friday.

Homework:

Class 37.5: Friday, 12/22/23

Warm Up:  Some cultures celebrate a character called Santa Claus, who delivers presents around the world in a sleigh.  This event occurs over a time interval known as Christmas Eve.  Starting from rest, if Santa were to deliver a present to every child who believes in him, how fast would Santa need to accelerate between stops in order to deliver all of the presents on Christmas Eve? Santa Claus from an Engineer's Perspective

Today:

Homework:

Class 37: Thursday, 12/21/23

Warm Up: 

None

Today:

  • Quiet Work Time

Homework:

Class 36.5: Wednesday, 12/20/23

Warm Up: 

None

Today:

  • Quiet Work Time

Homework:

Class 36: Tuesday, 12/19/23

Warm Up: 

1.  Why do we have tides?

2.  Why is there a high tide on the opposite side of the Earth from the Moon?

3. Which object is excerting a greater gravitational force on you right now, the Moon or the Sun?

4.  How is this related to black holes?

Today:

  • Check/review homework
  • Get the rest of the Unit 5 Handout  PDF  -- do pages 3-4 together. Filled-in Notes  Be very, very, careful. 
  • What to do on Friday? Special warm-up; then knots or songs?

Homework:

Class 35.5: Monday, 12/18/23

Warm Up: 

1.  What's the formula for the net force acting on the jogger in the video?

2.  Approximately how fast is the jogger in this video moving?

3.  If the jogger turned around and jogged the other way, would he feel any different?

4.  What must move in order for the person to experience simulated gravity... the space station, the person, neither, or both?  What does "move" mean in outer space?

Today:

  • Return tests
  • Questions about the test?
  • Start the new Unit? -- Uniform Circular Motion and Law of Gravitation
  • Finish the practice problems on Unit 5 Handout  PDF. Filled-in Sheet To make problem #4 easier, assume that the mass of the car ois 1,000kg.

Homework:

  • Complete the practice problems on p. 2 of the handout.  Solutions
Class 35: Friday, 12/15/23

Warm Up:  None

Today:

  • Little test -- Newton's Laws in 2D.

Homework:

  • None
Class 34.5: Thursday, 12/14/23

Warm Up: 

The ball is moving at a constant speed in a circular path. 

1.  What is the direction of its acceleration?

2.  How do we know this?

Today:

  • Check/review homework
  • Questions about the test?
  • Start the new Unit --  Circular Motion and Gravity Unit 5 Handout  PDF

Homework:

  • Prepare for tomorrow's small test.
Class 34: Wednesday, 12/13/23

Warm Up: 

A waiter at Bramble is delivering a chunk of bone (marrow in the middle), basted in synovial fluid, to some dinner guests.   Touching only the perfectly smooth and flat serving tray (also made of bone), the waiter must deliver the essentially frictionless dinner bone to the guests, placing it carefully so that it sits at rest on their table.

1.  Assuming that the bone and tray in the picture start at rest, describe what the waiter would need to do in order to make this happen? 

2.  Using the head-to-tail method, sketch the forces acting on the bone at various times during the waiter's feat. [Let's just assume that the bone is frictionless.]

 

Today:

  • Check/review homework
  • Work on practice Test #2 -- p. 11-12 of the handout.  On #2 and #4, change the coefficients of friction to 0.1 and 0.2, respectively.

Homework:

Class 33.5 Tuesday, 12/12/23

Warm Up: Cheryl wants to use some string and a nail to hang a treasured portrait of great-great-grandfather Ernesto as a young man.  The portrait is rather heavy.  Rank the three configurations on the right according to their risk of exceeding the breaking strength of the string.

Today:

  • Updated Schedule:
    • 2-D Newton's Laws test (a small one) is still on Friday
    • Next Wednesday and Thursday will be a dedicated retake day (for either or both tests).  If that won't meet all of your retake needs, you can do some retaking during FLEX or whenever we can work out a time.
  • Check/review homework
  • Practice Problem: #3 on p. 6
  • Turn-in any stuff that you have relating to project corrections

Homework:

Class 32.5: Friday, 12/8/23

Warm Up: -- video of the solution to this problem 

A 4 kg mass is suspended by an ordinary string from the ceiling of a fully-enclosed train car.  The car is on a level surface at sea level, and the angle shown remains constant.

How many of these can we deduce from this information?

A) The mass' direction of movement     

B)  The mass' acceleration

C)  The mass' velocity

C) The string tension

Today:

  • Check/review homework
  • Work time

Homework:

Class 32: Thursday, 12/7/23

Warm Up: In this next short unit, you will be finding all of the forces and accelerations in situations like those shown on the right.  What general problem-solving strategy(ies) might be helpful?

Today:

Homework:

Class 31.5: Wednesday, 12/6/23

Warm Up: One end of a rope is attached to the Gladys' belt.  Gladys is pulling directly downward on the other end. Assuming that the pulley and rope are massless and fictionless, how much downward force must Gladys apply in order to ascend?  Gladys weighs 500N.

Today:

  • Return tests
  • Distributions: Overall , A5/6, A7/8

Homework:

  • Optional retake on Monday, 12/11
  • Project corrections are due by Monday, 12/11
Class 31: Tuesday, 12/5/23

Warm Up: None

Today:

  • Test

Homework:

  • Optional retake on Monday, 12/11
  • Project corrections are due by Monday, 12/11
Class 30.5: Monday, 12/4/23

Warm Up:   If the coefficient of friction is zero...

1.  Which blocks affect the net force acting on the entire system?

2.  Which blocks affect the acceleration of the entire system?

3.  To which blocks would you assign numerically negative values for acceleration (during your calculations).  When?  Explain?

 

Today:

  • Return project grading sheets.  I will grade any late projects that are submitted by tonight.  Any project submitted after tonight will be graded with the projects that are submitted for corrections.  Groups submitting late projects after tonight will not have an opportunity to make corrections after the first grading.
  • Check/review homework
  • Any last questions about the test?
  • Start the new unit? Unit 4 Handout (Forces in 2D)  PDF

Homework:

  • Prepare for the test
  • Optional retake on Monday, 12/11
  • Project corrections are due by Monday, 12/11
Class 30: Friday, 12/1/23

Warm Up:   Draw diagrams showing all of the individual and net forces acting on the underlined protagonists in the situations on the right.

 

Today:

  • Turn in your project hard copies (or scan and turn them in by tomorrow tonight by 6:00PM -- I won't start grading before then)
  • Check/review homework
  • More review
    • Tricks misconceptions: 
      • 3rd law (use the correct member of the pair),
      •  Constant velocity makes problems easy (and doesn't mean there are no forces),
      • When there's no friction, the weight of a sliding object does not contribute to the net force
      • When you feel like you don't have enough information, know that you really do: draw a force diagram, write the two equations for net force, and work to fill it all in.
      • In multibody problems, don't use the wrong sign for acceleration when you're finding tension.
      • On this test, if a velocity is provided, there are only two situations in which it is helpful --
    • When to use kinematics equations -- acceleration is the link between the kinematics equations and the force equations.
  • What would you like to work on?

Homework:

Class 29.5: Thursday, 11/30/23

Warm Up:   At point C in the diagram on the right, the ball is in the process of bouncing off of the wall.  The ball's mass is 0.15kg, and its current velocity is zero.  At this moment, the ball is exerting a 2N rightward force against the wall.

1.  Draw a diagram showing all of the individual forces, and the net force, acting on the ball at letter C.

2.  Calculate the magnitude and direction of the ball's current acceleration.

3.  Is this situation possible?  Is it realistic?

Today:

  • Approximate Test Format:
    • 4 Short answer questions
      • Draw a diagram showing, calculating, and naming all of the forces acting on an object in some scenario.
      • 3rd Law example of action/reaction
      • Interaction of drag, weight, and normal force as an object falls
      • Create a series of diagrams showing and naming forces (with arrows indicating their relative strengths) acting on an object, based on a description of its motion
    • 6 Problems (each with multiple parts)
      • Weight
      • Sliding object with/without friction -- horizontal motion
      • Elevator Problems (vertical motion with tension)
      • System of multiple masses with pulleys a tabletop, and friction (or maybe no friction)
  • Work on the practice test at the end of the Unit 3 Handout (but not page 22).
  • Important Concepts:
    • Problem-solving:
      • Identify forces acting on an object.  Weight is the only non-contact force.  3rd Law is a helpful trick.
      • Write two equations for net force and set them equal (2nd Law and Vector Sum)
      • Define "the system" -- and define direction (positive or negative) for the system
    • Formulas:
    • Other concepts:
      • Friction
      • Drag

Homework:

 
Class 29: Wednesday, 11/29/23

Warm Up:   None

 

Today:

  • Rocket project work time -- last class time
  • Tomorrow, Friday, and Monday -- prepare for the test on Tuesday

Homework:

  • Divide the project work among group memgers and work on some at home.
  • The project is due on Friday.  There will be class time to work on it today, tomorrow, and probably part of Wednesday.
Class 28.5: Tuesday, 11/28/23

Warm Up:   An acceleration graph for a rocket launch with a parachute might look something like this.

1.  Locate these moments in time ("snapshots" from the project).

a. sitting on the launch pad

b. Thrust phase

c. Beginning of coasting phase

d. Apogee

e. Moment during descent when net force is highest

f.  Just before landing

g. Impact

2.  How would this graph look different if there were no parachute?

Today:

  • Clarification:  After I grade and return your projects, you can make corrections and submit them again for a higher grade.
  • Plan for the week:
    • Today -- rocket project work time
    • Wednesday -- rocket project work time
    • Thursday, Friday, Monday -- get ready for the test
    • Friday -- rocket project is due
    • Tuesday -- Test over Newton's Laws in 1D

Homework:

  • Divide the project work among group memgers and work on some at home.
  • The project is due on Friday.  There will be class time to work on it today, tomorrow, and probably part of Wednesday.
Class 28: Monday, 11/27/23

Warm Up:   Get together with your group and make a copy of the "[your names]Water Rocket Flight Model" spreadsheet in Google Classroom.  We're going to populate it together.

 

Today:

Homework:

  • Divide the project work among group memgers and work on some at home.
  • The project is due on Friday.  There will be class time to work on it today, tomorrow, and probably  Wednesday.
  • Tentative test day next Tuesday.
Link to classes 1-27.5