# What Are Artificial Satellites? Explain How They Are Put Into The Orbit?

If we throw a stone with some speed in a horizontal direction, it follows a curved path as it falls to the ground. If the stone is thrown with a higher speed it follows a path of bigger radius as it falls. We thus conclude that the higher the speed of the stone, the greater the radius of the curved path. If somehow we could throw the stone with such tremendous speed that the radius of its path became a little greater than the radius of the earth, the stone would fall around the earth, rather than on it. This is the principle of an artificial satellite.

In the case of a satellite, the centripetal force is provided by the gravitational pull of the earth. We can calculate the speed of a satellite at a distance r from the centre of the earth by equating the centripetal force with the gravitational force. Thus if m is the mass of the satellite and g be the acceleration due to gravity, we have

F (centripetal) = F (gravitational)

mv2 / r = mg.v2 = rg
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Satellites are the objects that orbit around the earth. Any satellite is kept in its orbit by the gravitational attraction of the body about which it is rotating. Many man made satellites are in circular orbits around the earth and once in orbit they do not need rocket motors to keep them in orbit. They are sufficiently far away from the earth's surface to have very little air resistance. They can remain rotating about the earth for many years. Satellites may have circular or elliptical orbits. Circular orbits are easier to handle mathematically and there many orbits, which are approximately circular.

A satellite orbiting near the earth would have a velocity of 7.9 kms-1 and would take 84 minutes to orbit the earth. It is impossible to have a satellite going around the earth faster than this speed unless it can keep its rocket motors going all the time to increase the force on it towards the earth. In practice it is impossible as there would be to great need of fuel. The higher the satellite, the slower will be required speed and longer it will take to complete one revolution around the earth.
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They are those created by man to revolve around planets to find information about them
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