| A | B |
|---|
| action | force that balances a reaction force |
| force | push or pull |
| unbalanced | a force that causes motion or a change in motion |
| acceleration | changing velocity |
| air resistance | frictional force from air molecules hitting an object as it moves through the air |
| friction | force between surfaces that goes against the motion of an object |
| mass | amount of matter of an object |
| motion | movement; a change in position |
| direction | line along which something is pointing, facing or moving |
| average speed | rate an object could travel between two points without changin speed |
| distance | length of a path an object travels |
| speed | rate of motion |
| velocity | description of the rate of motion of an object, including both speed and direction |
| action force | one of a pair of forces that causes a change of motion of an object |
| balanced forces | forces on an object, equal in strength and opposite in direction, that cancel each other |
| gravity | force that exists between any two objects because the objects have mass |
| laws of motion | Newton's three laws that describe the behavior of objects in terms of their masses, forces and motion |
| first law of motion | statement that an object will stay at rest, or continue to move in the same direction, at the same speed, unless an outside force acts on it |
| second law of motion | statment that an object accelerates when an outside force acts on it: force equals mass times acceleration |
| third law of motion | statement that all forces occur in pairs; for every action force, there is a reaction force of equal strength but opposite in direction |
