Here's why:

* Newton's Second Law of Motion: This law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Mathematically, this is expressed as:

* F = ma (Force = mass x acceleration)

* Stationary Object: A stationary object has zero velocity and therefore zero acceleration.

* Applying Force: When a force is applied to the stationary object, it overcomes the object's inertia (resistance to change in motion). This results in a change in the object's velocity, which means the object accelerates.

In summary: Force is the cause of acceleration. When a force acts on a stationary object, it causes the object to start moving, and therefore accelerate.