The focus of this chapter will be the topic of momentum. While it was introduced in dynamics, we will discuss it in more detail now. Recall that momentum depends on mass and velocity. The definition of momentum for speeds that don't approach the speed of light, is [br][center][math]\vec{p}=m\vec{v}[/math].[/center]Just as velocity is a vector, so is momentum. Recall that we define momentum because it is one of a short list of quantities that is conserved in nature by all isolated systems of any scale - from the scale of particle physics to that of cosmology. [br][br][b]Any time an object's momentum changes, some other object (or perhaps many objects) had momenta that changed in such a way that all the changes add up to a zero vector[/b]. Another way of stating this is simply that the momentum of the universe is constant. While that's not a useful definition for problem solving, it does make a point.[br][br]In the next section we will derive momentum and use it for problem solving.