| A | B |
|---|
| speed | a measure of how far something travels in a certain period of time |
| kilometers per hour | the number of kilometers something can travel in one hour |
| velocity | a measure of speed in a certain direction |
| inertia | the tendency of an object to stay at rest or to remain in motion unless an outside force causes a change |
| gravity | a force that acts to pull pairs of objects together |
| mass | the amount of matter in anobject |
| weight | the force gravity exerts on an object's mass |
| acceleration | rate,or change in speed or direction of movement |
| friction | ;slows an object's motion; a force that resists the movement of one surface past another surface |
| oil or grease | can reduce friction |
| sand | increases friction |
| air resistance | friction caused by gas molecules in the air hitting an object and slowing it down |
| streamline | to design smooth,rounded surfaces on an object so it slips through the air with the least possible resistance |
| action and reaction | forces work in equal and opposite pairs |
