Luke+Mikelonis

Physics of Pool **Categories:** Energy, Momentum, Newton's Laws

Energy
When you hit the ball with the cue stick in a game of pool, the kinetic energy from the cue stick is transferred to the ball. When the ball hits another ball, some of its kinetic energy is transferred to the second ball, causing it to start moving. Kinetic energy never disappears, it is only dispersed into other forms. Kinetic energy is equal to 1/2mv^2, meaning the only controllable factor is velocity. To control the amount of kinetic energy in the ball, you must be able to control it's velocity, which is possible with the cue stick.

Momentum
When a ball is hit by the cue stick, it gains momentum. Momentum is calculated by multiplying mass and velocity, so again, to control the amount of momentum the ball has you must control its velocity. When the ball collides with other balls, no momentum is lost, it is only transferred between them. This means the sum of the momentum of both balls after the collision is equal to the momentum of the first ball before the collision. However, as the ball moves, other balls are not the only force acting on it. As it moves, friction between the ball and table causes it to lose momentum over time and thus slow down.

Newton's Laws
Newton's first law states that an object at rest will stay at rest unless acted on by an external force. In a game of pool, all the balls are at rest when the game starts. They continue to stay at rest until they are acted on by any of the other balls, or the cue stick. Once in motion, they continue to stay in motion until they are acted on by another force, in this case friction with the table or a collision with another ball or the sides of the table.