Newton's Laws

an object will maintain its constant velocity unless acted upon by an outside force.

A ball will not spontaneously start to move on its own. You need to apply an unbalanced force to make it move.

• The acceleration of an object is directly proportional to the force on the object
• the acceleration of an object is indirectly proportional to the mass of the object.

Every action as an equal (in magnitude) and opposite (in direction) action.

Pushing on a wall. The action force is the person pushing on the wall, and the reaction force is the wall pushing back on the person.