# Physics final Lab.pdf - Maya Hansen Introduction Question...

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Maya Hansen 5/16/17 IntroductionQuestion: How does the percent energy loss in a ball rolling and bouncing off a wall compare to the percent energy loss in a ball dropping and bouncing off the floor? The question is asking about energy pertaining to collisions. It is assumed that energy will be lost during the collision of the ball with either a wall after rolling or the floor after being dropped because the ball will be bouncing, not sticking. To answer the question, two labs will have to be done; one where a ball is rolling into a wall and another where a ball is dropped onto the floor. These two labs will be treated as separate labs, with two data tables and two graphs, and then the results will be compared at the end. The loss of energy of the ball before and after impact will be used to compare the labs. However, It would be hard to accurately calculate the kinetic energy of the dropped ball and it would be equally as hard to calculate the potential energy of the rolling ball, so, we will be working with the assumption that KE = PE if we release the balls at the same heights during the labs. The kinetic energy of the rolling ball before and after the collision with the wall will be calculated withKE = ½ mv^2+1/3mv^2 (where m = mass of the ball and v = velocity of the ball). The reason why this equation is being used instead of KE=1/2mv^2is because energy lost to rotational motion also needs to be accounted for. This equation was derived from the equation KE = 1/2mv^2 + ½ I(v/r)^2 (where I= moment of inertia = 2/5mr^2 which is the moment of inertia for a hollow sphere which is what a tennis ball is, and r = radius of the tennis ball = 0.0306 +/- 0.00015 m). The average velocity before the wall and the average velocity after the wall will be used to calculate total energy before and after the wall (we are assuming all the energy is kinetic because the ball is on ground level). It is also assumed that the ball is rolling without slipping. Then we will calculate the percent of energy lost in the collision with (KEf - KEi / KEi)*100 = Percent Energy Lost. Even though we will be using velocity to calculate the kinetic energy, the graph’s independent variable will be the height of the ramp because the velocity directly relates to the height of the ramp and since the graph of the dropped ball’s data will be height v energy loss, the two would be easier to compare. The velocities will be taken as close to the wall as possible to minimize energy lost to rotation since the ball is rolling. Potential energy will be used to calculate energy loss of the dropped ball with PE = mgh(where m = mass of the ball, g =gravity = 9.81 m/s^2, and h = height of the ball). The heights used to calculate the energy will be the height that the ball is released at and the height that the ball bounces too because at those two points, the potential energy is equal to the total energy (the ball slows down to a stop at the highest point for a small amount of time). The percent of energy loss will be what is used to compare bounce off a wall to bouncing
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