| A | B |
|---|
| acceleration | The rate at which velocity, or speed, changes over time. It also happens when there is a change in direction. |
| astronomical unit | A unit equal to the average distance from Earth to the Sun or about 150 million km (93 million miles.) |
| ball bearings | Small metal balls inserted between two surfaces to reduce friction. |
| brakes | A device that slows and stops wheels that are turning. |
| cyclometer | A device that measures distance traveled and riding time on a bicycle. |
| deceleration | A decrease in speed over time. Gravity, friction, or air resistance can cause it. Since any change in speed or direction is defined as acceleration, this is considered a type of acceleration. |
| metric system | A system of measurement developed by the Franch National Assembly in the 1790's. Units are all related by powers of 10. Example: meter, liter, gram. |
| rate of acceleration | This is equal to the change in speed divided by the time it took to accelerate. |
| speed | The distance traveled in a certain amound ot time; rate of movement. The formula to calculate this is distance divided by time. (S = D/T) |
| velocity | The rate of motion (speed) in a particular direction. |
