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Momentum and Collisions (Y 40)


Keyword: Mechanics Lab

Demonstration Description:
In this experiment you allow two carts to collide on a level track and run into a spring that is attached to a force sensor. You will measure the position and velocity of the first cart and the force exerted by the spring while it is compressed. You can analyze your data to determine the following things from this experiment:

  • An experimental test of the conservation of momentum in elastic and inelastic collisions.
  • Determination of the maximum kinetic energy that is lost to non-conservative work in a completely inelastic collision.
  • Because you can only measure the position of one cart and the force exerted by the spring, you will analyze the one dimensional collisions in order to determine values that you cannot measure directly.
As the track is level, we do not need to consider changes in the gravitational PE of the carts and may take it to be zero. If we consider the two carts to be an isolated system (this is a good approximation so long as the friction forces are small), the only mechanical energy is kinetic, K. A collision is inelastic if some of the initial K is lost to non- conservative work.
A collision is elastic if no K is “lost.” A collision is completely inelastic if the maximum amount of K (consistent with conservation of momentum) is converted to non conservative work; this happens when the two colliding objects stick together. Sometimes that is what people mean when they refer simply to inelastic collisions.


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