| A | B |
|---|
| force | a push or a pull exerted on an object in order to change the object; force has size and direction |
| balance forces | a set of forces on an object that cancel one another out so that there is no overall force on that object; the combined force is the same as zero force; balanced forces will not cause a change in the motion of an object |
| newton | the SI unit for force |
| unbalanced forces | a set of forces exerted on an object that change the motion of that object; the combined force has size and direction; unbalanced forces are needed to make an object start moving, speed up, slow down, or change direction |
| net force | the combination of all of the forces acting on an object |
| velocity | the speed of an object in a particular direction |
| Newton's laws of motion | a series of laws developed by Isaac Newton that describe the relationship between force |
| friction | a force that opposes motion between two surfaces that are in contact |
| inertia | the tendency of an object to resist being moved or, if the object is moving, to resist a change in speed or direction |
| acceleration | the rate at which velocity changes over time; an object accelerates if its speed, direction, or both change |
