Setting Up The Experiment

• The basic form of the experiment consists of two carts lined up. These may be blocks of wood with wheels on, placed on a flat surface, or purpose-built weighted pieces of metal arranged on a track. One of the carts is set in motion and made to collide with the other cart. To demonstrate different features of the experiment it is possible to vary the mass and elasticity of either cart.
  
  

Elastic Collisions

• Elastic collisions are those in which kinetic energy (energy of bodies due to movement) is conserved. In the case of carts this is demonstrated by putting a rubber block on the end of either cart. When two carts of equal mass have an elastic collision, their relative velocities are reversed. If a moving cart collides with a stationary cart, they switch places, and the previously stationary cart moves off. If they are of unequal mass, then their relative momentum (velocity x mass) is reversed.
  
  

Inelastic collisions

• Inelastic collisions are those in which total kinetic energy is not conserved; some energy is transformed into heat and sound. In the cart collision experiment this can be demonstrated by two metal carts without rubber on them. In a perfectly inelastic collision, the two bodies do not move away from each other after colliding, but continue moving together at a changed velocity.
  
  

The Scientific Explanation

• In all of the above experiments, the overall average momentum is conserved:
  
  P = m x v
  
  Where P is momentum, m is mass and v is velocity. However, in elastic collisions, kinetic energy is maintained, whilst some is lost in inelastic collisions. This is because kinetic energy is proportional to velocity squared:
  
  Ek = 1/2 x m x v^2
  
  Where Ek is kinetic energy, m is mass and v is velocity. In inelastic collisions the object traveling fastest does not transfer all its energy to the other body, and the other body only continues to move at a lower speed.
  
  

Advanced Forms of The Experiment

• More advanced forms of the experiment may involve laser measurement to accurately determine the velocity of the carts, enabling them to be plotted on a graph. This requires purpose-built equipment.