Lab Momentum

Rebecca
Nov. 2013
Kyle, Mat, Alex

Lab M7
Conservation of Momentum

Abstract: This experiment involved the use of gliders on an air track which nearly isolates the colliding system from external forces to create low friction totally elastic and inelastic collisions. Seven different collisions were made, four elastic and three inelastic. The collisions consisted of only two gliders with varying masses and speeds. Each glider cart was equipped with a flag, and its passage through a photogate timer was timed. These measurements will allowed the velocities of the collision partners to be measured before and after they collided with each other. The obtained values do show that initial momentum and final momentum are equal irrespective of their masses and initial velocities. The results show that momentum and kinetic energy of the system is conserved during an elastic collision while only momentum is conserved during inelastic collision. Kinetic energy is not conserved during an inelastic collision. This was found by dividing the final kinetic energy by the initial kinetic and getting a number that was close to one. Which is was fairly close in most cases.

Introduction: The purpose of this experiment is to study the principle of conservation of momentum in collisions using two bodies. The amount of kinetic energy lost in elastic and inelastic collisions is also calculated.
The theory of momentum in an isolated collision is that the total momentum before a collision is equal to the total momentum after the collision in an isolated collision regardless of mass or speed as long as the object is moving in a straight line and is not rotating. The equation used to calculate the before kinetic energy should then be equal to the after kinetic energy equation. Pi = m1v1i + m2v2i = m1v1f + m2v2f = Pf The m is the mass of each glider and the velocity, v was obtained from the times in which it took for the flag of the gliders to pass through a photogate.
In this experiment an air track was used along with three gliders two of almost equal mass and one slightly heavier. The times of which the masses passed through the photogates was recorded using logger pro.
An air track was first leveled and all three gliders were weighed, labeled and the flag length measured. Then the gliders were placed on the track with the bumpers facing each other to produce elastic collisions. All collision occurred between the two photogates. The first situation that was modeled was with gliders of equal masses where one of the gliders was placed near the mid-point of the track and the second cart was pushed towards the other with an initial velocity towards the stationary glider. The second situation mimic the first except using gliders of different masses. In the third collision two gliders of approximately the same mass were push towards each other with different velocities. Collision four was the same except involved gliders of different masses. For the last two collisions the two masses and Velcro to allow them to stick together to have an inelastic collision. In collision five one glider was stationary and the other was push into it. After the collision the gliders moved off together as one unit. This collision was more difficult to perform and need to people to push the gliders to ensure that both had different velocities. And in collision six both gliders had initial velocity but the second mass chases the first and catches up with it and collides.

The analysis involved doing all the calculations to find the velocity as well as the momentum of each glider. Care was taken to ensure that the times contained a positive and a negative since time was used to calculate the velocity which is a vector quantity and therefore needs direction. All this information was then placed on a chart showing the times, velocity, momentum and kinetic energy for each collision before and after.

Discussion: For each of the collisions performed the total momentum was mostly conserved and when it wasn’t may have been due the error. Such as the blower of our air track did not have the right sized tub and was leaking and therefore there was greater friction in our collisions. But other than the results of our collisions were relatively close to one which shows that momentum is indeed conserved irrelevant of the mass and velocity of the gliders. The first four collisions performed were elastic with some small errors due to the fact that the air track was bowed in the middle and there for many have accelerated due to the slant in the air track and that there was a leak in the blower tube allowing for more friction. In collision one where one mass was stationary they transferred their kinetic energy and after the collision the primarily stationary mass was moving with the same velocity as the other mass. There were a few assumptions made in this experiment. One of the big ones being that there was no friction and the other being that the air track was completely leveled.

The purpose of this experiment is to study the principle of conservation of momentum in collisions using two bodies. We will also calculate the amount of kinetic energy lost in elastic and inelastic collisions.

This experiment was done to show that the total momentum before a collision is equal to the total momentum after the collision in an isolated collision regardless of mass or speed.