Force & Motion

Push, pull, and how forces change movement

A force is a push or pull that can change an object's motion. Forces have both size (magnitude) and direction. When the forces on an object are balanced (equal in all directions), the object stays still or moves at constant speed. When forces are unbalanced, the object accelerates in the direction of the net force. Friction is a force that opposes motion between surfaces in contact. More mass requires more force to achieve the same acceleration (F=ma). Gravity pulls objects downward with a force equal to their weight (W=mg).