Here's why:

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

* Momentum (p) = mass (m) × velocity (v)

* Velocity is the rate of change of an object's position. Since an object at rest isn't moving, its velocity is zero.

* Therefore, if the velocity is zero, the momentum will also be zero.

In simpler terms: If something isn't moving, it doesn't have any momentum. It's not carrying any "motion energy."