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) × velocity (v)

* Velocity is the rate of change of position, meaning how fast an object is moving and in what direction.

* When an object is standing still, its velocity is zero.

* Since velocity is zero, the product of mass and velocity (momentum) is also zero.

Therefore, an object at rest has zero momentum.