| A | B |
|---|
| air resistance | The force exerted by air against objects that are moving through the air. |
| Aristotle | A Greek philosopher who believed that the heavier an object is, the faster it will fall toward Earth. (This is a false belief.) |
| force | Any push or pull. Newton discovered a mathematical formula that shows how this causes a change in the speed or direction of an object; force = mass x acceleration. |
| Galileo | A scientist who found that heavy and light objects fall at the same rate. |
| gravity | The pull of a body or object on all other bodies or objects. The closer and/or larger the body, the more pull. |
| mass | The amount of "stuff" (matter) in an object or objects. A lead ball has more of this than a cotton ball of the same size. |
| vacuum | A space that has no matter, not even air. Therefore this space has no air resistance. Scientists on earth test Galileo's theory in one of these chambers. |
| weight | A measure of the force of gravity on an object. The common units for measuring this unit are the pound in the English system and the newton in the Metric system. |
