Hockey players colliding

This simulation is designed to give you some idea of what happens during a collision between two hockey players. Note that the "red player" is the player from the team with the red uniforms; the "black player" is the player from the team with black uniforms.

Note that the simulation must be re-started for any changes to take effect.

Right is taken to be the positive direction; a velocity or momentum to the left is negative.

Momentum is the weight in pounds multiplied by the velocity.
Kinetic energy, the energy associated with the motion of the players, is one half of the weight in pounds multiplied by the square of the speed.

This simulation illustrates a collision between two hockey players. The elasticity determines how much kinetic energy is lost in the collision. The elasticity will always be between 0 and 1; an elasticity of 1 means that no kinetic energy is lost (like a Superball bouncing off a hard floor), while an elasticity of 0 means that much of the kinetic energy is absorbed by the players and their pads.

A typical collision between hockey players is not very elastic, so a low setting of the elasticity makes sense. Feel free to adjust that until you get what you think is the most realistic value - the initial value of 0.2 is just an educated guess.

One key thing to note here is how much energy is absorbed by the players in the collision. Compare the kinetic energy before to the kinetic energy afterwards - all the missing energy is absorbed by the players.

Another key factor in a collision is the change in velocity, which can be found for each player by subtracting the velocity before the collision from the velocity afterwards. Because this change occurs very quickly, there can be a lot of stress on different parts of the body, particularly the head and neck.

Note that the momentum is always conserved in a collision, so it is the same before and after. The kinetic energy after the collision, however, is less than the kinetic energy before the collision unless the collision is elastic (elasticity = 1).

Special cases to consider include:
Equal weights, equal speeds, elastic collision (elasticity = 1).
Equal weights, equal speeds, completely inelastic (elasticity = 0).
One player 3 times heavier than the other, equal speeds, elastic collision.
Equal weights, black player stationary before the collision.

Set all those up and see what happens.

Created by Andrew Duffy, Boston University Physics Department.

Last update March 15, 1998