| A | B |
|---|
| force | a push or a pull |
| newton | the SI unit for strength of a force |
| force | this is described by its strength and by the direction in which it acts |
| net force | the total of all the forces acting on an object |
| balanced forces | the net force of an object is 0; the object's motion does not change |
| unbalanced forces | the net force does not equal 0; the object's motion changes |
| friction | a force caused by two objects rubbing together |
| the strength of the force of friction | this depends on two factors - how hard the surfaces push together and the types of surfaces involved |
| types of friction | static friction, sliding friction, rolling friction, fluid friction |
| static friction | between two things that are not moving |
| sliding friction | when two objects slide past each other |
| rolling friction | when one object rolls over another |
| fluid friction | when a solid moves through a fluid, like water or air |
| gravity | a force that pulls objects toward each other |
| mass | how much matter is in an object; this stays the same no matter where it is |
| two factors that affect the gravitational attraction between objects | mass and distance |
| weight | measures the force of gravity on an object; this can change if the force of gravity changes |
| the force of gravity increases | this happens when two objects move closer together |
| objects with a large mass | these objects have a greater force of gravity |
| objects with a small mass | these objects have a lesser force of gravity |
| free fall | the force of gravity is an unbalanced force that causes the object to accelerate |
| 9.8 m/s/s | the rate at which a free falling object accelerates downward towards Earth |
| free fall | when theo only force pulling on a falling object is gravity |
| air resistance | friction caused by air |
| air resistance | a force that pushes upward on falling objects |
| terminal velocity | as an object falls to Earth, its velocity increases - this is the greatest velocity it reaches |
