# Universal Gravitation

## Gravitational Field Strength

### The table below shows the Gravitational field strength at the surface of several celestial bodies:- ## Gravitational Field Strength and Altitude

### As the distance from an object increases, the Gravitational field strength gets smaller. Due to this, the value of 'g' is reduced at higher altitude. The graph below shows how the value of 'g' varies in relation to Height:- ## Newton's Law of Universal Gravitation

### As has been shown previously, the Gravitational field strength varies greatly between locations. In 1687, Isaac Newton published 'The Principia', containing his work on Gravity. Within this publication, Newton had devised a general rule which would allow the calculation of the Force of attraction due to Gravity between any two objects at any separation. This formula is called Newton's Law of Universal Gravitation :- ## Example 1 -

### A pupil of mass 50 kg is sitting on the Earth surface and is attracted to the Earth which has a Mass of 5.97x1024 kg. What is the Gravitational Force that the pupil experiences if the radius of the Earth is 6.38x106 m? ## Example 2 -

### What is the Gravitational Force between two pupils sitting 2 m apart if both pupils have a mass of 50 kg ? ## The Schiehallion Experiment

### This experiment was performed using the Munro Schiehallion in Perthshire, Scotland. 