## Wednesday, December 1, 2010

### Energy Bar Charts and Project

Today we first started to work on our bar chart packets. They have to be done by today, or you have to come in during study hall or homeroom. If you were absent, then check with your group to get the answers.

Then, Mr. Finley called up our groups to check our homework, the bar charts for the skier problem and lifting a ball problem.

To check this we are going up to Mr. Finley computer with our groups. We are to view two PowerPoints with all of the answers on it, and compare our answers. This will be available tomorrow as well, so don't worry if you didn't get to it.

Then we were called up to the front by groups to be told about a project. We have to watch a video about an elephant jumping on a trampoline, see 5 thing in the video that relate to energy, and choose 2 that you can analyze and share in class. We have to draw or describe initial and final states. Then we have to include your choice of a system. Third, we have to create three different representations that show the changes of energy that occurred. You can use a picture, bar chart, number statement, descriptions, etc. Finally we have to answer if the the elephant situation is realistic in terms of physics and energy. Remember, this is a group project. You don't need to start it at home.

Here is the video:

Tonight's homework is:

Nothing as of 4:30. As we all know, Mr. Finley posts homework by 4:00 so it is safe to day there is no homework.

Here is the webpage

I am somewhat confused about what the difference between energy conservation and energy constant. Can somebody clear up what these two terms mean and how they are different?

Thanks!

MK

1. I think that energy conservation is when the before and after bar charts show that both sides equal out to 0. For example when there is 100J of energy on the before side, there would be -100J on the after side or in the work done column. When energy is constant, both sides equal out exactly. So when the before side is 50J, the after side has to be 50J too. I'm not sure though if both sides can equal out if the before and after sides are both negative and not positive.

BB

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3. Thanks, but how can something have negative energy? I believe there is only negative force and negative work. Energy can either be equal to or greater than 0. Otherwise it would have less than no energy. I think what you are trying to say is that the energy conservation is when it starts at one value and ends at 0. I am not sure though.

MK

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5. What was the work and system for the elephant jumping on trampoline problem??

AR

6. i think constant energy is when the beginning(before side) energy is equal to the the ending energy(after side) and conserved energy is when the energy in the beginning isn't the same as the ending.

AR

7. I think AR is right. That makes sense. I think the system was the elephant and the earth. The earth has to be part because it has Gravitational Potential Energy.

8. The earth is whats making the gravitational potential energy so it can't be in the system. I put that the trampoline is in the system while the elephant and the earth are doing the work. Yes, I do now agree with Michael because I forgot that when energy is conserved that it doesn't have to equal out to 0.

BB

9. I believe that you always include the earth in a system talking about Gravitational Potential Gravity. I would say that the elephant is the system of interest along with the earth. I also don't think the trampoline did any work.
MK