AP Physics – Conservation of Momentum - HRSBSTAFF ….doc

AP Physics – Conservation of Momentum We’ve studied the law of conservation of energy and found it to be a very powerful thing in the world of physics. Another very powerful conservation law has to do with momentum. This is the law of conservation of momentum. Momentum is Conserved in an isolated system. “Isolated system” means that there are no external forces acting on the thing. The type of interaction that involves changes to momentum that we will deal with are called collisions. (Although not all of them are what we think of as a collision, as we shall see.) The law of conservation of momentum means that for a collision in an isolated system, momentum must be conserved. This means that the total momentum of the system before the collision must be equal to the total momentum after the collision. Here is the momentum before the event and is the momentum after the event. Collisions can be very complicated. They can get so complicated that they can’t really be solved as a matter of fact. To simplify things, we will deal with collisions involving two bodies. We will also deal with one-dimensional collisions (like between balls rolling along a track), or else two dimensional collisions that occur at right angles. This helps out a great deal. Imagine trying to deal with a violent collision between two cars. Before the collision you have two bodies in motion that have momentum. After the collision you’ve got thousands of them – all the bits and pieces of the cars flying off in every imaginable direction. Collisions can be classified according to the energy interaction that takes place: Elastic collision ( kinetic energy is conserved Inelastic collision ( kinetic energy is not conserved Perfectly inelastic collision ( objects stick together and have the same velocity. Application of Conservation of Momentum: On the AP Test, you will only be given the equation for momentum, p = mv. From this you will have to derive the formula for a two-body co