What is gravity?

The force of gravitation affects everything on Earth. This invisible force is the reason why, for example, apples fall to the ground.

Sir Isaac Newton discovered that there is a gravitational force that attracts any two objects in the universe. This attraction depends on the mass of the objects and the distance between them. The greater the masses of the objects, the greater the attraction. Moreover, the further the distance, the less the attraction.

	The magnitude of the force of attraction (F) is given by: where m1 and m2 are the respective masses of the two objects, r is the distance between them and G is a constant known as the gravitational constant (G = 6.672 · 10-11 Nm2/kg2).

	Mass of the Earth: 5.98 · 1024 kg Mass of the Moon: 7.35 · 1022 kg Mean distance between the Earth and the Moon: 384 400 km

The Sun and all planets attract each other with their gravitational pull. As the Sun has by far the greatest mass, all planets rotate around it. The Moon rotates around the Earth for the same reason – the Earth is over 30 times more massive than the Moon. We see the attraction of the Moon from the tides: it tugs at the water in the oceans and creates high and low tides.

The Moon rotates around the Earth