Here is a worksheet that I am going to give you in class

Jumping Worksheet

I will bring copies, but it is here also.

I will give you the following (with constants)

Here are the sample chapter 6 questions from class:

Here are the questions we used in class today.

Chapter 5 practice (pdf)

I am going to assume that something weird happened and that maybe you understand chapter 2 stuff better than that.

Here is your one chance for redemption. Answer these two questions (ON YOUR OWN) and turn them in Friday at the beginning of class. I will grade them and give you up to 15 points.

NOTE: You have plenty of time, so I will expect much more detail and a much clearer 'presentation' than I would on an in class test. Think about showing the solution more than 'getting the answer'. Also, I can tell if you worked on this independtly. If you cheat and, the consequences will be severe. You are welcome to use your text, but not other people.

1) Derive the gravitational gravitational potential energy. Make the assumption that U_grav = 0 J when the separation between the two objects goes to infinity.


2) The LCROSS space probe recently crashed into the surface of the moon. This crash shot a lot of moon stuff (dust) off the surface of the moon. Some of the dust was projected to reach 50 km above the surface of the moon. Remember, that there is no air on the moon. How fast would a piece of moon be initially going so that it reaches 50 km above the surface?

Sorry, my mistake. Hopefully the website is back to the way it should be. There is still the problem on the PLAB 223 page with the vpython stuff. I will try to fix that later.

First, Test 2 is going to mostly cover Chapters 4-5.7. You probably still need to know some stuff from chapters 1-3. I am not going to ask any questions about potential energy (which starts in section 5.8).

Here are the equations I am going to give you:



Also, I will give you any constants you need (even the speed of light which you should probably just memorize)

You asked for it, so here is a sample question that could be asked on the test:

Your friend, who is trying to write a VPython program to model the motion of Halley’s comet orbiting the Sun, has a program almost written, but lines of code are missing: the actual calculation of the gravitational force on the comet, the application of the momentum principle, and the updating of the position.
(a) Write the missing lines of code. You do not have to get the VPython syntax exactly correct, but you do need to use the names of variables your friend has created. Here is the unfinished program:

This was announced in class, but I am saying it again.

On the next test, there will be 5 questions, not 4. You will only be graded on the 4 you choose though. The 5th question will be one about numerical calculations in vpython (so you can consider it to be optional).

To get you started with vpython, first go to

http://vpython.org

And download both python and vpython.

Next, go to the labs page and start working on the labs. You could probably get through Lab 5.

VPython Labs


Also, if you would find it helpful, I could meet with anyone working on VPython (or other stuff as well) in the student lounge (Pursley room 109) on Wednesday at 3:00 (before the PLAB 223).

I am pretty sure I made a mistake in class today. I think I said that for an object moving in a circle, the rate of change of momentum was:



This is just plain WRONG. That is the rate of change of the momentum unit vector, so the rate of change of the total momentum would be:



With the direction still towards the center of the circle. Actually, I did this wrong on purpose to see if anyone was paying attention.

Also, I said I would post a link to the derivation of the above. Here it is.

Just in case you need help pacing your reading, you should aim to finish reading Chapter 4 by Next Monday at the latest. You could probably finish it by Friday.

In case you wanted some more details on the fake videos, here are some links with more details. (in no particular order)

- Hancock throws a boy
- Elephants can't jump
- Kobe Bryant jumping over a car
- Kobe Bryant jumping over snakes
- Up! and throwing a gps
- Giant Water Slide Jump
- Professor Splash Jumps into 1 foot of water

Finally, if you think Tracker Video Analysis was cool, here is a short-quick tutorial:

There is an SPS (Society of Physics Students) meeting this Thursday at 2:00 PM in Pursley room 105. If you are a physics major, you should go. If you are thinking about being a physics major, you should go. If you think physics is awesome, you should go. s

Test 1 is on Friday.

It will cover chapters 1-3. I will give you these equations:

1. I am uber-pissed at WebAssign for this stupid re-access thing. Totally not my fault. Short story: WebAssign said I was using questions from a book that I didn't use in class. This is because I had never officially declared a book with WebAssign. Now that I DID declare a book, some of you users have to re-access. If that is the case, WebAssign claims you got a refund (no idea how).

If you are having ANY problems with webassign, email them at support@webassign.net - they usually respond quickly.

2. If you are sick. Don't come to class. I only take attendance becuase it helps me learn names and the university requires it (but it is not part of your grade). You will not miss anything except for my bad jokes if you are away. If you need to miss a test, it is no big deal. Stay home and chill.

I think I have correctly enabled WebAssign auto extensions. This means that you should be able to give yourself an extension. If it doesn't work, email me.

Here is the question we stopped at on Friday:

So, here is the question I gave in class on Wednesday:



How do you solve it?

a) Start with the fundamental principle:

From this, I can get a relationship between the momentum at t = 15 (call it p₂) and p at t = 10 seconds (p₁):



I know p₂, so I can solve for p₁. I get:



Now, plugging in my values:



b) I want to find the position at t = 15 seconds and I know the initial position. This is what I want to use:



If I know the average velocity, then I could rearrange this to get:



So, how do I get v_avg? If I assume this is moving slow, then I can say that:



And, if I assume that the momentum changes at a constant rate, then:



This means that the second position would be:




Let me write this out in parts v_avg t would be:




So, r₂ will be:

I made this simple game. Well, it is not really a game, but it could be. You can fire rockets on this spaceship using your arrow keys. The rockets exert a constant force in that direction. Play with it. What do you have to do to move at a constant speed? How can you move in a circle? Can you move to the right but have a force to the left?

Learn more about this project

Someone else has created video podcasts for the Matter and Interactions text.

http://web.me.com/sspickle/PHYSICS/153_Podcasts/153_Podcasts.html

Maybe you will find them useful.

I suggest starting on the reading of chapter 2. Try to finish it by Monday

If you want to keep up with the reading, I think aiming to finish chapter 1 by Monday would be a good plan.

This is not quite all you need to know about vectors, but if you don’t feel comfortable you could start here.

http://blog.dotphys.net/2008/09/basics-vectors-and-vector-addition/

Here is a sheet that I might use some of in class.

Vector Worksheet(pdf)

but now you have it for your own also.

I posted the first WebAssign homework.

To log into WebAssign, the easiest way is to go to blackboard and click on WebAssign in the PHYS 221 page. This should automatically log you into webassign.

I think there is a way to get to webassign (for you) without going through blackboard. You might have to change your password in webassign or something to get there directly. If someone knows this answer, let me know.

Welcome to PHYS 221.

Here are a couple of quick notes:

• Blackboard is evil. I don’t use it except when I have to. All of the useful stuff will be posted here.
• 
  
• Check out the syllabus, you may find it useful.
• 
  
• I strongly encourage you to keep up with the WebAssign homework. It is very easy for you to neglect that, but it will make things harder later.
• 
  
• I really don’t have anything else to say