Newton's Three Laws in Words and Formulae. Inertia and More.

You probably had them memorized when you were in middle school, but by now you've forgotten. Here's a quick refresher.

An object at rest remains at rest. An object in motion remains in motion unless acted upon by an outside force.

If F=0, then a=0

(no Force, no acceleration)

When you throw a ball on earth, gravity acts upon it as an outside force, which eventually stops its motion. If you throw a ball in space, it will never stop. It will go on forever until it encounters something that makes it stop, such as the gravitational pull of a star.

The acceleration of an object is directly proportional to the force on it and inversely proportional to its mass.

f/m=a (force divided by mass equals acceleration)

OR

f=ma (force equals mass times acceleration)

Basically, a smart car will accelerate much faster than a dump truck. The smart car has smaller mass, so the force applied to it results in higher acceleration. Apply the same amount of force to a dump truck, which has higher mass, and acceleration will be lower.

For every action, there is an equal and opposite reaction. Forces occur in pairs and the force on one object is equal and opposite of the first force.

A > B + -B > A (Equal and opposite)

Take a look at the skaters below. Their force on each other is equal, but in opposite directions.