The product of an object's mass and velocity in vector form is called its linear momentum. You can use momentum to predict the effects of collisions. If you have ever played a game of pool or billiards, you probably have a feel for how momentum works.     You will come accross two types of collisions here. In elastic collisions, the objects do not stick together, while in inelastic collisions, they do. The actual definitions add some other important factors dealing with energy, but for now, these will help you visualize the collisions.

Bouncing Ball
       When two balls are dropped to the floor with one on top of the other, some fascinating things happen when the balls hit the floor. Many students have seen this demonstrated in classes-- use a basketball for the bottom ball and a baseball or softball for the top ball for an interesting result. (Be careful as rebound speeds can be high!)  
Updated 7/20/99

Equivalence of Conservation of Angular Momentum and Conservation of Energy Methods for Satellite Velocity Calculations

      In teaching Introductory College or University Physics to undergraduates or advanced high school students, problems involving elliptical orbits are frequently presented with the objective of enriching the students' understanding of orbital mechanics. An exercise nearly always encountered in these first-year classes consists of relating the velocity of a satellite (whose mass is treated as being insignificant compared to that of the central body) at its apoapsis to the velocity of the satellite at its periapsis. Some students will choose to solve the problem using conservation of angular momentum, while others will use conservation of energy relationships.
     The teacher is able to assure the students that the relationships are equivalent (both physical laws must hold), though it is by no means obvious that this is so by inspection alone.
Updated 8/9/99