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May the Force Be with You

The F. the m and the a in Newton's formula are very important concepts in mechanics. The F is force. a push or pull exerted on an object. The m is mass. a measure of how much matter is in an object. And the a is acceleration, which describes how an object's velocity changes over time. Velocity. which is similar to speed, is the distance an object travels in a certain amount of time.

Let's restate Newton's first law in everyday terms:

­An object at rest will stay at rest, forever, as long as nothing pushes or pulls on it. An object in motion will stay in motion, traveling in a straight line, forever, until something pushes or pulls on it.

Physicists use the term inertia to describe this tendency of an object to resist a change in its motion. The Latin root for inertia is the same root for inert, which means lacking the ability to move. So you can see how scientists came up with the word. What's more amazing is that they came up with the concept. Inertia isn't an immediately apparent physical property, such as length or volume. It is, however, related to an object's mass. To understand how, consider the sumo wrestler and the boy shown below.

­Interestingly, Newton wasn't the first scientist to come up with the law of inertia. That honor goes to Galileo and to Rene Descartes. In fact, the marble-and-ramp thought experiment described previously is credited to Galileo. Newton owed much to events and people who preceded him. Before we continue with his other two laws, let's review some of the important history that informed them.