Acceleration- the rate at which velocity changes over time Action/reaction force pair- objects that act on one another causing equal and opposite reactions Balanced force- when two or more objects exert equal force on an object, resulting in zero motion Unbalanced force- when two or more objects exert unequal force on an object, resulting in motion of the object Centripetal force- force that keeps an object moving in a circle Distance- how far an object travels Reference point- a location to which another location or object is compared Relative motion- motion depends on the position and motion of the observer Gravity- the force that objects exert on each other because of their masses

Inertia- an object’s resistance to change in speed or direction of motion Mass- a measure of how much matter an object is made of Momentum- a measure of mass in motion. The product of an object’s mass and velocity Newton’s first law- an object in motion stays in motion and an object at rest stays at rest unless acted upon by an unbalanced force Newton’s second law- acceleration of an object increases with increased force and decreases with increased mass Newton’s third law- every action has an equal and opposite reaction Speed- a measure of how fast something moves through a given distance over a definite period of time Time- how long it takes an object to get to a certain point Velocity- speed in a given direction