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)

* Resting means the particle has a velocity of zero (v = 0).

* Therefore, when you multiply the mass by zero velocity, the momentum becomes zero.

In simpler terms: A particle at rest isn't moving, so it doesn't have any momentum.