Momentum is mass in motion.  Its formula looks like this:

p = mv    where p=momentum, m=mass, and v=velocity. 

To change an object's momentum, you must give it a force for a length of time. 

So,        Dp = F Dt.  

In most cases, the object's mass does not change, so Dp may be written as: m Dv.  

Thus,     m Dv = F Dt.

Believe it or not, momentum is actually another form of the equation F=ma. Here's the proof:

F=ma

F = m Dv/Dt

F Dt = m Dv   

But this is what we began with a few lines above!  This means it isn't really a new concept at all, just a new way to look at something we've already done.  Thank you for recycling.  :-)