Mike Tomlinson, age 14, of 1hunnsville, N. Y., for his question:

Does the earth both revolve and rotate?

These words crop up nowadays in news items, Mankind has at last put his own satellites into orbit and we are naturally interested in their movements. This leads us to a fresh interest in the established heavenly bodies, such as the earth. We read that these bodies revolve and rotate and since the two words sound so much alike we wonder whether they are not two names for the same movement.

Rotating and revolving are two very different movements, though both of them involve turning. The earth rotates by spinning on its axis like a top. Each rotation takes about 24 hours, during which time first one side then another gets a chance to face the sun. While facing the sun, each side is, of course, in daylight. !:s the earth rotates, it turns around into the shadows of night. This rotation of the earth continues without pause day and night.

While rotation goes on, the earth is also revolving around the sun. Each revolution is a 600 million mile journey around its orbit. It takes our fat old earth one year to make one revolution traveling at the amazing average speed of 181 miles a second.

So far as we know, all heavenly bodies both rotate and revolve. Even our monster sun rotates around its own axis. It also revolves in a huge orbit around our cartwheel Galaxy. All the stars we see are part of our Galaxy and all revolve around like a giant pinwheel., The little manmade satellites also revolve and rotate.  They rotate by tumbling end over end as they revolve in an orbit around the earth.

There are reasons why the heavenly bodies rotate and revolve. Though separated by vast reaches of space, there are very strict traffic laws to keep them in their proper places. Maybe you have wondered why the earth does not crash into the sun or why the moon does  not fall down onto the earth. These heavenly bodies are kept in their places by gravity and centrifugal force, the traffic laws of the universe and the same laws which govern the little satellites.

Gravity is the great force which pulls objects towards a planet or sun. Centrifugal force pulls an object away from the force of gravity. It is the force which builds up when you swing a ball on a string around your head. If you let go, the ball swings away from and not towards you.

The earth builds up terrific centrifugal force as it revolves around its orbit. The sun's gravity pulls at it, spinning it around. Because of the opposing centrifugal force it falls, not towards the sun, but around and around it. Its orbit is the path where its centrifugal force exactly balances the sun's pull of gravity. A permanent manmade satellite will have the right speed to build the centrifugal force to balance exactly the earth's pull of gravity.