Here's why:

* Momentum is a measure of an object's mass in motion. It's calculated by multiplying the object's mass (m) by its velocity (v): Momentum (p) = mass (m) x velocity (v).

* If an object is at rest (velocity = 0), its momentum is zero, even though it has mass.

* The larger the mass or velocity of an object, the greater its momentum.

Example:

A stationary car has mass but no momentum. However, a moving car with the same mass has momentum because it has velocity.