Momentum and Collisions Conservation of Momentum Chapter 6: Section 2

Learning Targets Describe the interaction between two objects in terms of the change in momentum of each object Compare the total momentum of two objects before and after they interact State the law of conservation of momentum Predict the final velocities of objects after collisions, given the initial velocities P3.5a

Law of Conservation of Momentum Consider a situation where two pool balls are on a billiard table ▫Initially ball B has zero momentum because it is stationary ▫When ball A collides with ball B, ball B gains momentum while ball A loses momentum ▫The momentum that ball A loses is exactly equal to the momentum that ball B gains  This relationship is known as the Law of Conservation of Momentum

Conservation of Momentum According to the Law of Conservation of Momentum m 1 v 1,i + m 2 v 2,i = m 1 v 1,f + m 2 v 2,f Frictional forces will generally be disregarded in most conservation of momentum problems For an isolated system, the law of conservation of momentum can be stated as follows: ▫the total momentum of all objects interacting with one another remains constant regardless of the nature of the forces between the objects

Conservation of Momentum: Another Example Another example of conservation of momentum occurs when two or more objects with no initial momentum begin moving away from each other ▫Imagine two skaters pushing away from each other  The skaters move in opposite directions with equal but opposite momentum so that the total final momentum is zero ▫This example relates to Newton’s Third Law of equal and opposite forces