Ten, nine, eight, seven… zero – lift off. These words sound like music to an astronomer’s ears. As the countdown progresses, the rocket’s engines fire and give it the required push to tear through the atmosphere and escape the earth’s gravitation.
These rockets take astronauts and artificial or man-made satellites into space. The satellites are used for communication, weather monitoring and research. But how do satellites stay up without falling down, you might ask?
The Rope Trick
Take a strong rope. Tie a small stone to one end to make a sling. Rotate the sling using one hand, you will notice that the rope straightens out and becomes tight as the sling rotates. As soon as you stop rotating, the rope slackens again. Why does the rope tighten on being rotated?
The answer to this question will provide the answer to our query about satellites. When the sling is rotated, there are two forces acting on the stone. The force of rotation, which tries to take the stone away from you and the force applied by your hand, which tries to pull the stone towards you.
While you are rotating the sling, the two forces balance each other out and hence the stone keeps going round and round. If you release the sling midway, the sling will fly off.
A satellite also rotates around the earth. The gravitational pull of the earth (the force which pulls everything towards the ground) is like an invisible rope which keeps the satellite from flying away.
One of the two opposite forces acting on the satellite is the force of gravitation, which tries to pull the satellite towards the earth. The other force is that which is created by the rotation of the satellite around the earth. This force tries to take the satellite away from the earth.
An orbiting satellite has these two forces balanced out and hence the satellite goes round and round the earth like the stone in the sling.
Why does a satellite come down?
As time goes by, the satellite loses its speed, making the gravitational pull stronger than the force pulling it away. This makes the satellite come crashing down to earth. Most of the material gets burnt even before it reaches earth because of the intense heat generated due to friction with the atmosphere.
Some like the Mir space station unleash a fiery spectacle.