The branch of mechanics discussing motion of bodies and its causes.

A physical quantity that moves, stops, or changes the speed and direction of a body.

• First Law: Objects remain at rest or in uniform motion unless acted upon by a force.
• Second Law: Force equals mass times acceleration (F = ma).
• Third Law: For every action, there is an equal and opposite reaction.

• Mass: The quantity of matter in a body.
• Weight: The downward force exerted by Earth on a body.

The force per unit mass that Earth exerts on a body.

The product of mass and velocity. It is a vector quantity.

In a closed system, the total momentum remains constant if no external force is applied.