Originally Posted by mcguyver
Is not momentum simply the kinetic energy at a given point in time?
At any rate, a BB with more mass will be less affected by gravity.
No, and not true. Gravity affects all things equally reguardless of mass. Member the saying of dropping a bowling ball and a feather at the same time (in a vaccum) and they will hit the ground at the exact same time? It's true! Another mind blowing fact: if you shoot a bullet perfectly horizontal and drop a bullet at the exact same instant, they will BOTH hit the ground at the same time!
In general, the momentum of an object can be conceptually thought of as how difficult it is to stop the object, as determined by multiplying two factors: its mass and its velocity. As such, it is a natural consequence of Newton's first and second laws of motion. Having a lower speed or having less mass (how we measure inertia) results in having less momentum.
The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity.
As you can see momentum and work/energy are completely different things.
A heavier BB will lose it's kinetic energy SLOWER due to it's momentum being greater.