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media type="file" key="physics project1.mov"We will be testing the conservation of momentum with a skateboard and a medicine ball. A group member will be on the skateboard holding the medicine ball at rest. The person will then throw the ball until both the person and the ball come to a complete stop. We plan to find the momentum by first finding the velocities as the two objects collide. For the medicine ball, we will solve a bomber problem, and for the person, we will pull them with a scale at a constant speed in order to find the Fa. With this information and the mass of the person and the skateboard, we will be able to find the velocity as it pushes the ball away. With the two velocities we will be able to find the final momentum to compare to the initial momentum to see if it was conserved.

Equipment- skateboard, medicine ball (12kg), hard surface

Safety Precautions- We need to make sure that we are very careful when are when the group member pushes the ball away. If the floor is too slippery, they may hurt themselves. We also need to take caution because the medicine ball has a heavy mass and it is important that the area it will be thrown to is clear.

__Procedure-__ For our experiment, we chose to do a recoil problem. Heather will be sitting on a skateboard holding a medicine ball. While on the skateboard, Heather will throw the medicine ball with as much force as possible. We wait until both the ball and Heather came to a complete rest and then we mark where they land. With this information, we are able to use their distances in two different problems in order to find their velocities. In order to find the velocities we have to do two separate problems- A bomber problem for the medicine ball, and an Fnet and ViVfDAT problem to find Heathers initial velocity. With these two velocities, we are able to find the momentum of the ball and Heather after the collision to compare it to before the collision to see if the momentum was conserved. In order to collect data we are going to mark many locations. The first location is where Heather will be initially sitting on the skateboard. Next we marked the location where the ball hit the ground (on the first bounce). We must get that location because that represents the dx in order to solve a bomber to find the velocity of the ball! Another distance we recorded was the distance from the ground to the bottom of the medicine ball which was our Dy. The last location we must mark is where Heather comes to a rest. This distance from the starting point represents her recoil. As well as the distances, we also took the masses of the medicine ball, and Heather and the skateboard. We use these masses to help solve for the velocity.

To find the velocities we did two types of problems. For the medicine ball, we used a bomber problem. We used the distances we measured for the displacement in the x and y. Then we knew that the acceleration in the y was -9.8, and the acceleration in the x was 0. Next we knew that the Vi in the Y was 0. With this information, we solved for time in the Y. Then we brought it over to the X column to solve for the Vi in the x direction. We did three separate problems for each trial. To find Heather's velocity, we had to do a two part problem. First we had to use Fnet equations in order to find her acceleration (which we needed to solve for ViVfDAT later on). We found that a -Ff was equal to Fa, so we need to find miu (we knew that Fg is equal to Fn, so we didn't need to do a separate equation). We know that Ff is equal to miuFn, so we needed to find the miu. To find miu, we used a spring scale and pulled Heather at a constant speed in order to find the force we used (Fa). With this information, we used the equation F=ma in order to find the acceleration. We found the acceleration and plugged it into a ViVfdat equation to find her velocity. For each trial, we changed her recoil distance which was represented by Dx. With these velocities we were able to see if the momentum was conserved!

Conclusion:

Considering the relatively low percent errors, momentum was conserved in our experiment. The momentum at the start was zero, because Heather, the skateboard and the ball were all at rest. At the end, however, we didn't get Heather/skateboard and the ball's momentum to equal zero, but the two numbers were close to each other. No outside force acted upon heather or the ball; the Heather simply threw the ball, and gravity and friction stopped ball while the force of friction stopped Heather/skateboard. Because our momentums weren't exactly the same before and after, we could have measured the distance from the ball to where it landed wrong. We had trouble trying to find the starting point of the ball, so we tried to measure as best we could from the middle of the ball to the point where it landed. Another problem could have been that Heather was not throwing the ball consistently enough. After three trials of tossing the medicine ball, her throws could have been less forceful.