Week of March 22, 2010

If I could go back in time and talk to myself about one concept that would make it easier to learn in the future, I would talk to to myself about work-energy bar charts. First, I would tell my past self that an energy bar chart represents a process that occurs to a system. I would also tell myself that in order for work to be done there has to have been an external force.

Second, I would tell myself that it is important, when making bar charts, to get the labeling at the top right. That way anyone trying to read your bar chard can understand it. Ki+Ug,i+Us,i+W+Kf+Ug,f+Us,f+(delta)int. This all means initial kinetic energy+ initial gravitational potential energy+initial elastic potential energy+ work+ final kinetic+ final gravitational potential energy+final elastic potential energy+ the change in internal energy. Thirdly, I would tell my past self that when you add up the initial energy and the work it should equal final energy. If the final state has more or less total energy than the initial state than positive or negative work must have been done by an outside force, so you should draw a bar in the work column. The number sentence should always be equal.

Fourthly, i would explain energy transfers to my past self. Energy transfers is when you have one type of energy in the before section of your energy- bar chart and another type (but the same amount) of energy in the after section of the bar chart. For example, if the initial state of a bar chart is a marble is high up in a marble ramp [friction free] , it might have 3j of gravitational potential energy, and the final state is it moving (it is almost at the bottom of the ramp) it may have 3j of kinetic energy. no work was done, the energy was just transfered. The night that we practiced doing bar charts with the money examples is a good thing to show my past self. Those helped me understand the whole work section of the work-energy bar charts.

this link explains work-energy bar charts:

http://www.physicsclassroom.com/CLASS/energy/u5l2c.cfm

Week of March 1, 2010

If I could travel back in time and talk to myself about energy and systems, I would first show my self the elephant video. The elephant video helped me understand the different types of energy, how it was transfered, and when the system has these types of energy. The first type is Kenetic energy, I would tell myself that the system has this type of energy when it is accelerating. Then, I would say that gravitational potential energy was when something was at the peak of falling or about to fall. I would show myself Mr. Finley dropping a dictionary. Next, I would tell myself that Elastic potential energy was when something had the power to stretch another thing, like when Aage flung the chalk at the classroom door using a rubber band. Then i would look at the problem with the girl pushing the box on a color changing floor to help me out with the last energy form. To help me learn to identify the things in a system I would talk to myself about all the things that are affecting it, because anything affecting the system cannot be in the system. Then i would ask myself if the system has gravitational potential energy. If it did I would tell myself that I then needed to include the earth in my system. for initial and final states i would try to explain to myself that there are normally two choices for initial and final. For example, when Mr. Finley was dropping the dictionary the initial state could be when it was on the ground and then the final would be when he was holding it. Or, the initial could be when he was holding it and the final would be when the dictionary was in mid-air. It all depends on what kind of energy you are trying to explain that your system has. And for calculating work, I would yell at myself, "YOU CANNOT HAVE CENTIMETERS IN YOUR NUMBER SENTENCE!" because I forget that every time.