Class 21 Friday, 3/5/21

Warm Up:  

A spring hangs from the ceiling.  When a mass m is attached to the end of the spring, released from that position, and allowed to come to rest, the end of the spring is a distance x lower than before the weight was added. 

 

1.  Which method below will not work for finding the spring constant k?  Why?

  • Method 1:  Set the weight of the hanging mass equal to the spring force; mg = kx.  This gives us k = mg/x

  • Method 2:  Assume that the gravitational PE that is lost gets converted to spring PE, so mgh = 1/2 kx2 .  Since the height lost is equal to the stretch distance (x), we find that k = 2mg/x.

 

2.  Sketch a graph of PE, KE, and OE versus time.

Today: 

Homework:

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:

Class 18 Tuesday, 3/2/21

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

Today: 

  • Briefly discuss the homework.
  • Blue opportunity for test retake.

Homework:

Class 17 Monday, 3/1/21

Warm Up:  

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

2.  How did it get that nickname?

3.  In the context of physics energy problems, some forces are called conservative, and others are referred to as non-conservative.  Can you guess the difference between the two?  (Probably not)

 

Today: 

Homework:

Class 16 Friday, 2/19/21

Warm Up:   None

Today: 

  • Thank you to those of you who turned your remote test in as a Google Doc!  That made my life easier.  And if you use "Tiny Scanner," I discovered that you can send jpegs of your scan to your Google Drive and put them in a Google Doc.

  • Return tests and discuss grading.  Retake opportunities will be on Tuesday, 3/1 (Blue) or Thursday, 3/4 (Gold and Remote) after break.

  • I will post a video explaining all of the test problems and questions, and I will share that tonight with anyone who has finished the test.

  • Optional Retake of Unit 4 test

Class 15 Thursday, 2/18/21

Warm Up:   None

Today: 

  • Test for everyone -- Gold (in person), Blue, and Remote -- Gravity, Circles, and Kepler

Class 14 Wednesday, 2/17/21

Warm Up:   The graphs above show the net force applied to an object as it moves to various positions, relative to its origin.

1.  Calculate the amount of work represented by each graph.

2.  Can you describe the overall change in kinetic energy in each of these scenarios?  Explain.

3. Sketch your own graph of net force vs position for an elevator that travels from the 1st to 2nd floor.   Assume that the elevator starts and ends at rest.  Calculate the total work for the motion that you graphed.

4.  In number 3, it takes energy to lift an elevator.  Where does the energy go?

5.  How are these force vs. distance graphs similar to graphs of acceleration vs. time?

6.  Which of the graphs below is possible?

Today: 

  • Last chance for questions about the Unit 5 Test or the Unit 4 Test Retake

  • Notes:  Potential Energy and Energy Conservation Equations

 

Class 13 Tuesday, 2/16/21
Warm Up:   Do you know how to make a cloud in a 2-liter bottle, using water and a small amount of smoke?  Can you explain the process in terms of work and energy?

 

Today: 

  • Review the homework

  • Test review

  • 10-15 multiple choice over...

    • Centripetal motion

    • Law of Gravitation

    • Kepler's Laws (all 3)

  • 7 problems -- solve for some variable in the related formulas.

    • 3 Uniform Circle problems --
      • see chart on the right for possibilities
      • Focus for vertical circles will be on top or bottom (not sides)
    • Law of Gravitation

    • Kepler's 3rd Law

    • Something relating to the formula for velocity of a satellite in circular orbit

    • Something relating to the formula for g.

  • Updated Formulas:

  • "4 minute drill" Solutions

 

Class 12 Monday, 2/15/21

Warm Up:   How are "g-forces" dangerous to pilots?  What can they do to mitigate the danger?

Today: 

Get the Unit 6 Packet -- Work and Energy.  Begin the new unit.  If we don't get through #6 on page 2 of the packet, we will finish the notes on Wednesday.

 

Practice:  Complete "Work and Energy Practice Problems" #1-5 on pages 3-4 of the Unit 6 Packet. Some answers/solutions  Solutions to 3 and 4

Class 11 Friday, 2/12/21

Warm Up:  

1.   Suppose a 1,000kg car is traveling through a loop-the-loop at a constant speed.  The radius of the loop-the-loop is 5m, and the car is traveling at the slowest speed that will allow its wheels to remain in contact with the "road" at the top of the loop.  Calculate the car's velocity.  Then identify and calculate all of the individual forces acting on the car at each drawn location. 

2.  Can a human run through a loop-the-loop?

 

Today: 

  • Discuss the homework

  • Reminder -- optional Unit 4 Retakes (Newton's Laws in 2-D) are next Friday for all students (Gold, Blue, and Remote).

Homework:  

Class 10 Thursday, 2/11/21

Warm Up:  

0.  Where are all of the videos that I have recorded during class?

1.  What is a geosynchronous satellite?

2.  What's the difference between a geosynchronous orbit and a geostationary orbit?

3.  What is a space elevator?

4.  Does raising an elevator require a force greater than the elevator's weight?  Explain.

Today: 

  • Review the homework

Practice: 2019-2020 Test: Circular Motion, Gravity, and Kepler's Laws  Answers/Solutions

Class 9 Wednesday, 2/10/21

Warm Up:   From 2016-2017 EPS 200...

The Sun, Earth, and Moon are continually spaghettifying one another.  On Earth, we see the effects of this spaghettification in the form of tides.

1.  What causes spaghettification?

2.  How much gravitational force do the Sun and Moon each exert on 1,000,000 pounds of water on the Earth's surface?  How much space would that much water occupy?

3.  Even if there were no water on Earth, there would still be tides, just as there are tides on the Moon.  Describe these tides.

4.  Why do we always see the same side of the moon?

5.  Is the Earth's 24 hour rotational period speeding up or slowing down over time? Answer

Today: 

  • Review the homework

Practice:  Gravity/Circles Practice Test -- 2018-19 Test  Solutions to 18-19 Gravity/Circles Test  Video explaining solutions (These are my solutions that I used to grade the tests; the solutions are not necessarily written so that they are easy to follow.)

Class 8 Tuesday, 2/9/21

Warm Up:  

According to the diagram on the right...

1.  At what approximate date is the Earth orbiting with the fastest speed?  When is it orbiting the slowest?

2.  Rank our seasons in order of length. Answer

3.  What's this, and why am I showing it to you?

Today:  Probably a short class today.  We're going over the last new thing in this unit -- Kepler's 3rd Law.

Practice: Packet P. 6, # 14, and 15.

Class 7 Monday, 2/8/21

Warm Up:   None -- but we will have a short Google Meet

Today: 

Class 6 Friday, 2/5/21

Warm Up:   None -- but we will have a short Google Meet

Today: 

Class 5 Thursday, 2/4/21

Warm Up:  

1.  Approximately how fast is the space station rotating in 2001 - A Space Odyssey?

2.  If the jogger turned around and jogged in the opposite direction, how might he feel different?

3How does NASA simulate weightlessness? Are astronauts and candles weightless when they are in the international space station, orbiting Earth?  What word best sums up their motion?

 

Today: 

  • Questions relating to the test?

  • Blue people -- I have hard copies of the Unit 5 Packet in the classroom.  I had intended to hand them out to you on Tuesday.  Sorry.

  • Continue Notes:  Circles, Gravity, Kepler  Solutions

    • Fix problem #10, if we haven't already

    • Check out online textbook chapter 6.5

    • Law of Gravitation -- skip #4 and do a different example

Reading (optional):

 

Homework:  .

 

Class 4: Wednesday 2/3/21

Warm Up: 

A ball is tied to a string, and someone is holding the string, swinging the ball in circles at a constant speed of 10m/s.

1.  Define acceleration.

2.  What is the direction of the ball's acceleration?

3.  How is the ball's acceleration related to its speed?

4.  How is the ball's acceleration related to the length of the string?

 

Class 3: Monday 2/1/21

Warm Up: 

A waiter is delivering a chunk of bone, basted in synovial fluid, to some dinner guests.   Touching only the serving tray (also made of bone), the waiter must deliver the dinner bone to the guests, and place it carefully on their table.  Assuming the guests' table is to our left in the picture, describe what the waiter would need to do in order to make this happen?
Class 2: Friday 1/29/2021

Warm Up: 

1. 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.  Assume that all pictures are supported by two strands of string.

2. What do static equilibrium and dynamic equilibrium mean, as they relate to physics problems?

  • Google Meet: 

    • If you haven't already noticed, we're switching back to Google Meet.  It seems to be more stable, and there's a ding when hands are raised.  The link is in the assignments section of Google Classroom.  I will try to keep it there at the top.  If it drifts down, let me know.  I want the link to be the same for both blocks, so I can't use the class Meet link on the Google Classroom main page.

    • Discuss having more hands-on labs/projects.  At our current pace, we're right on schedule to cover the same content as in a normal year.

    • Hand out the next packet.  Gold people will probably need it on Tuesday.  I will leave them in the office for the remote people.

    • Discuss the homework.

    • Work through some example problems from packet p. 5 and 6. -- one static equilibrium problem and one dynamic problem that is only in equilibrium in one dimension.

  • Practice: 

Class 1: Thursday 1/28/2021

Warm Up: 

A 1kg mass is suspended by a string from the ceiling of a fully-enclosed train car.  The angle shown remains constant.  The train is on a level surface.

1. Describe the motions of the mass and the train car in qualitative terms.

2.  How can we find the tension in the string?

3.  How can we describe the motions of the mass in quantitative terms.

 

  • Take photo for seathing chart.

  • Google Meet: 

    • Think about whether you would like to have more hands-on labs and projects, understanding that this would require more "asynchronous" learning outside of class.

    • What's coming up in the final 2 quarters:  Course Syllabus

    • Some Semester 2 logistical things:

      • I am teaching two blocks of this class (3 and 4), and each block has its own Google Classroom.  Grading is easier for me this way. I will try to keep all of the assignments the same for the two blocks.

      • We are going to try Zoom, rather than Google Meet. This will allow me to see more students at once.  The limit in Meet is 16.  This may be especially helpful if Block 3 people want to join Block 4 for the day, or vice versa.  If there are problems with Zoom, we may go back to Meet.

      • I will put the Zoom link in Google Classroom.

      • We will have a Zoom every day, except on special occasions.  I will not be listing the meetings as assignments in Google Classroom; just remember that we always have one and that you should either attend or watch the video.  If you want a description of what we are doing for the day, that will be here on my website.

      •  I will stream and record at least one of the day's Zooms (probably block 3).  At some point after class I will add the video link to the Physics Semester 2 YouTube playlist.

      • When you're remote, you can attend either class.\

    • Get the Unit 4 Packet, if you haven't already picked it up.

    • Begin Newton's Laws in 2-D -- Bodies on Inclines problems

  • Practice: