On Earth gravity keeps our feet firmly on the ground and the gases in the atmosphere. It makes anything we throw up in the air soon come back down again to the ground. The Earth's gravity is very powerful, so how can we beat it and launch objects into space?
Newton worked out how gravity could be beaten by speed. However, to
beat gravity an object must be launched from the Earth at the colossal
speed of 28,000 km/h. At this speed it will be able to circle around the
Earth. Because there is no air in space, there is nothing to slow the object
down, and it will continue circling at the same speed, in orbit. It will
become an artificial satellite of the Earth.
A cross-section of the Earth's atmosphere. (above) The air is thickest
at the bottom. It thins out with increasing height until it merges into
space. But faint traces of air remain even at 200 km high.
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Isaac Newton drew this diagram (left) to show how to beat gravity. If you throw a ball faster and faster, it will travel farther and farther before failing back to Earth. At a very high speed indeed, the ball will "fall around the Earth" and enter orbit. |
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The American physicist Robert Coddard (1882-1945) launched the first liquid-fuelled rocket in 1926. This fuel system overcame the major obstacle to launching an orbiting satellite which was the weight of solid fuels. If a rocket is to reach a speed great enough to escape the Earth's gravitational field, it needs a thrust greater than the weight it is carrying. |
