Here's why:

* Force: Gravity is a force, and forces are measured in Newtons.

* Newton's Second Law: This law states that force (F) is equal to mass (m) times acceleration (a): F = ma.

* Gravity's Acceleration: The acceleration due to gravity is approximately 9.8 m/s².

Therefore, the force of gravity acting on an object is calculated by multiplying its mass (in kilograms) by the acceleration due to gravity (in m/s²), resulting in a force measured in Newtons.