What is momentum and how is it different from speed/velocity?

Answer 1

Momentum used to be called "inertia" and is a measure of what is required to change a body's state of motion. It depends on both the velocity ( that is, a vector quantity since it has direction ) and the mass with the product of the two being the momentum.

Comparing a light bullet and a heavy bullet traveling at the same speed, one must note that the heavier bullet has greater momentum. Momentum is always conserved ( even when energy APPEARS not to be --e.g. in an inelastic collision ).

Answer 2

Momentum is the product of mass and velocity. It is conserved when there is a symmetry in that direction of space. For example, in a horizontal collision between football players or billiard balls it is conserved. For an object falling in a gravitational field, it is not (there is a preferred direction, and the ball's velocity continues to increase).