PURPOSE

To learn about conservation of momentum and kinetic energy by studying different types of collisions in two dimensions.

EQUIPMENT  collision movie clips, VideoPoint® software application.

RELEVANT EQUATIONS

Momentum of a particle:  

Total momentum of a system:  

Kinetic energy:  

DISCUSSION

In this experiment, you will verify the conservation principles studied previously. They are: conservation of momentum (C of M) and conservation of kinetic energy (C of KE) in the case of an elastic collision. In the case where two bodies collide, the conservation of momentum is simply expressed as:

Keep in mind that the vector nature of the velocities is important here. In motion along a straight line, the vector direction is indicated with a plus or minus sign. In two dimensions, this equation means that the vectors are equal, component by component, before and after the collision.

The collisions you will study in this experiment are in the form of video clips of gliders on an air table that will be analyzed using the application VideoPoint®. You will follow the development of the collision in each case by logging the positions of each of the gliders frame-by-frame. The motion can then be analyzed to confirm conservation of momentum.

Another conservation rule applies only to collisions that can be termed elastic. This usually refers to the condition where no mechanical energy is lost to heat during the collision. If any or both of the bodies are permanently deformed, that is, any deformation that occurs during the collision does not "spring back", then the collision is inelastic and conservation of energy does not apply. The worst case scenario for this type of collision is called completely inelastic when the two colliding bodies stick together after the collision. The conservation of kinetic energy can be expressed in general as:

Using the conservation of momentum for any collision, and the conservation of kinetic energy for an elastic collision permits us to determine one or more unknowns.