# Newton's Three Laws in Words and Formula. Inertia at Rest, and More.

## Yes, you do need to memorize these.

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

## 1. Law of Inertia

**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 **F**orce, no **a**cceleration)

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.

## 2. Law of Acceleration

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

f/m=a (**f**orce divided by **m**ass equals **a**cceleration)

OR

f=ma (**f**orce equals **m**ass times **a**cceleration)

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.

## 3. Law of mutual action

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.

## Comments

I like the examples you give for each of the three laws. It puts a picture in my mind so I can comprehend the formula better. This is a very nice, concise summary of these 3 laws.

Newton was a pretty smart guy. Not only is he credited with these three laws, he created calculus as well. His laws are the basis for the principles that engineer's use to design a lot of the things that we see every day. These concepts are very important for everyone to understand, so I am very excited to have read this hub.

Short but very academic :)! I had never really interested in Science but those Newton's theory really made sense. BTW, the only science equation that never leaves my mind is Einstein's relativity theory, E=mc2

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