| A | B |
|---|
| reference point | the object that appears to stay in place |
| motion | an object's change in position over time when compared with a reference point |
| speed | the rate at which an object moves; it depends on the distance traveled and the time taken to travel that distance |
| velocity | the speed of an object in a particular direction |
| acceleration | the rate at which velocity changes |
| force | a push or a pull |
| Newton (N) | the SI unit of force |
| net force | the force that results from combining all the forces exerted on an object |
| friction | the force that opposes motion between two surfaces that are touching |
| gravity | a force of attraction between objects that is due to their masses |
| weight | a measure of the gravitational force exerted on an object, usually by the Earth |
| mass | the amount of matter that something is made of |
| positive acceleration | acceleration in which velocity increases |
| negative acceleration | acceleration in which velocity decreases |
| centripetal acceleration | acceleration that occurs in a circular motion |
| balanced force | when the net force on an object is zero and there is no change in an object's motion |
| unbalanced force | when the net force on an object is not zero and there is a change in an object's motion |
