### Newton's Law of Universal Gravitation

**In Words**

Every body attracts every other body in the universe
with a force that is directly proportional to the product of the masses of the two bodies
and inversely proportional to the square of the distance between their centres.

**In simple words, this means that any object that has mass, automatically attracts another object that has mass!**

Study this diagram.

These two masses are attracting each other with a force called a Gravitational Force. The distance between them, from center to center, is called **r**.

This force can be calculated from this equation :

**G** is called the **Universal Gravitational Constant**.

And it is ALWAYS

**6,67 x 10**^{-11}**N.m**^{2}**kg**^{-2}.

Chill, it's on the data sheet!

**Some of the constants from the Data Sheet.**

**Calculate the Gravitational Force of Attraction between these two masses.**

**The diagram can then be drawn like this, showing TWO forces.**

Althought only ONE force was calculated, there are actually TWO forces, one per mass. This is because of Newton's Third Law :

The two forces are the same size even though the masses are different.