In a nutshell, Gravity is the force that pulls things towards the centre of the Earth.

We study gravity to learn more about the Earth and to make our lives easier, to prosper economically and socially.

Before we get started, let's define a few of the key terms, which we will use to describe this universal force.

Gravitation - is the force that pulls or attracts all bodies in the universe towards one another. It is the force that keeps the planets in their orbit around the Sun and that keeps objects on the surface of the Earth.

Mass - is the amount of material that an object contains. All objects have mass. Mass floating in space weighs nothing, but it acquires weight in the presence of gravity belonging to a second mass. A good example of this is our Solar system. The planets all have different masses, and are attracted to each other by varying amounts. Jupiter, for example, has a mass that is 318 times the mass of Earth. Earth in turn has a mass 81 times greater than that of the Moon.

Density - is a measure of how tightly the material in a mass is packed. An example of this might be a snowball. If the snow is light and fluffy, the snowball you make will be less dense than the one you make from wet heavy snow. A dense object feels heavy for its size.