Julia+&+Hannah's+Collision+Experiment

=1D Cart Collisions Lab= September 21, 2009
 * Participants**: Julia Kravitz and Hannah Mollmark
 * Purpose**: The purpose of this lab is to confirm the law of conservation of momentum.
 * Lab Documents**: [[file:1D Collsions.doc]]

Below is an example of our process of viewing the video, plotting points, and determining momentum. The first video we watched that we got the above information from: media type="file" key="Collision 1 small.wmv" width="300" height="300"
 * Brief Description of Experiment**: We started by observing videos of collisions that had been previously designed and recorded. As we watched, we plotted points on the actual video which were then displayed on a graph. The points showed the movement of the carts throughout the collision. We recorded the mass of the carts and, along with the velocity from the slope of the points, we were able to detemine the initial and final momentums. By comparing these, we could tell if the momentum was conserved.
 * Data**:
 * [[image:Collision_Data.JPG width="694" height="400"]]

Sample Calculations:** Calculation// || The momentum in kilograms per centimeters per second was calculated by taking the mass in kilograms and multiplying it by the velocity of the cart (which is distance in cm divided by time in seconds). momentum = mass x velocity || kinetic energy = 1/2 x mass x velocity squared || Calculation// || The percent difference is calculated by subtracting the final total number (momentum or kinetic energy) from the initial total number (momentum or kinetic energy), dividing that by the initial total number (momentum or kinetic energy), and then mulitplying it by 100. ||
 * //Momentum
 * //Kinetic Energy Calculation// || The kinetic energy in joules was calculated by multiplying one half times the mass in kilograms and velocity, which is in centimeters per second, squared.
 * //Percent Difference
 * Results**: The purpose of this lab was to confirm the law of conservation of momentum. By observing collisions and going through the processes and calculations, this law was essentially confirmed. For Collision 1; Version 1, Collision 5; Version 2, Collision 6; Version 1, and Collision 9; Version 1 the calculated initial and final momentums were very close. For Collision 3; Version 1, the change in momentum was a little greater.

1. Momentum is a vector quantity (it has a direction associated with it). This is relevant for some of the collisions you anaylzed. Which ones and why? The only collision we analyzed that this applied to was Collision 9 Version 1. The carts moved toward each other which caused them to collide and ricochet in opposite directions. Because of this, some of the velocities were negative due to the direction they traveled: the vector quantity of momentum. 2. Calculate the percent difference between the initial total momentum and the final total momentum for each collision. Which collision had the largest percent change in momentum? Collision 1 Version 1: 9.12% Collision 3 Version 1: -8.87% Collision 5 Version 2: -39.87% Collision 6 Version 1: -43.57% Collision 9 Version 1: 1.83% The collision that had the larges percent change in momentum was Collision 6 Version 1. 3. If you had not correctly scaled the video (the scale line was drawn incorrectly, for instance), it would have no effect on your data's ability to support or refute the law of conservation of momentum. Explain why this is so. If the scale had been done incorrectly, it would have no effect because the initial and final momentums calculated would still be comparable. True, the scale might have been wrong which means the velocity would be a little off or have the wrong units, but because the scale isn't changed at all during the observation of one collision, the results from it can be accurately compared despite correct or incorrect scaling. 4. You may have observed the carts slowing down as they moved across the track before the collision. Suppose you have two velocities for a cart; one just after it was pushed and one immediately before the collision. Which would be better to use to evaluate your prediction and why? It would be better to use the velocity immediately before the collision. This is because it would be a better comparison to what happens after the collision. Because the cart slows down, the speed at which it travels immediately before the collision is what affects or transfers to the other cart during and after the collision. 5. Calculate the percent difference between the initial total kinetic energy and the final total kinetic energy for each collision. Which collisions had large percent changes in kinetic energy? Collision 1 Version 1: 17.39% Collision 3 Version 1: -25.59% Collision 5 Version 2: 2.17% Collision 6 Version 1: 11.12% Collision 9 Version 1: -6.7% The collisions that had large percent changes in kinetic energy were Collision 1 Version 1 and Collision 3 Version 1. 6. Examine the group's analysis to see how each collision was characterized (as elastic or inelastic). How can you tell if a collision will be inelastic? You can tell if a collision will be inelastic by determining the kinetic energy before and after the collision. If it is different before and after it is elastic. Another way is by determining if the objects stick together or loose energy. If they do either of these, they are normally inelastic. We think the experiment produced a valid and reproducible result because we used experiments that had been previously done and recorded. This eliminates the act of recreating the collisions which could very easily cause changes and therefore different results. In addition to this, the object we used to scale every collision was the level which was on the table. Using the same object to scale would help in reproducing the experiment as accurately as possible. Our experimental results may differ from certain accepted or expected values due to a few reasons: the location and accuracy of the points we plotted on the video, what part of the line we took the slope from, rounding in calculations, etc. An improvement to the experiment would be to determine where, or how far into the video, to begin plotting points. In addition, being able to see the entire track on which the carts travel would help in determining the positions of the carts. Also, knowing whether or not to plot points for both carts starting at the same time and what to consider the initial velocity for certain carts that entered the frame moving would be helpful. **
 * Lab Questions**:
 * Conclusion: