Rollercoasters are pulled downwards by the Earth’s gravity. The Universe is made of matter. Matter is held together and moved by forces. One of the basic or fundamental forces is the gravitational force—also more simply known as gravity. Any piece of matter from a pinhead to a planet has gravity. It pulls or attracts other matter. The biggest large lump of matter in our daily lives is the Earth. Every time you jump up in the air, you fall back down to Earth again. The Earth's gravity pulls us and other objects towards it, keeping our feet on the ground.
The gravitational force was first identified by the English scientist Sir Isaac Newton (1642–1727)—supposedly on observing an apple fall to the ground. He realised that the Earth pulled all objects towards it by gravity. He extended this to all matter. It was only because the Earth was very large compared to the apple that the apple moved back to the Earth and not the other way round.
Newton also realised that the nearer an object, the stronger its gravitational force on other objects; the force becomes weaker with increasing distance. The Earth is very big and very near, so for us its gravity is strong. However, as you travel further away its gravity weakens, although even at the distance of the Moon, it is still strong enough to keep the Moon in orbit around the Earth.
Gravity is one of the four fundamental forces of nature, along with electromagnetism, the nuclear strong force and the nuclear weak force.
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