Here's why:

* Mass: The more massive an object is, the harder it is to get it moving, and the harder it is to stop it once it's moving. This means a more massive object has more momentum.

* Velocity: The faster an object is moving, the more momentum it has. A car moving at 60 mph has more momentum than the same car moving at 30 mph.

The mathematical formula for momentum further emphasizes this relationship:

Momentum (p) = mass (m) x velocity (v)

So, momentum is directly proportional to both mass and velocity. The greater the mass or velocity, the greater the momentum.