Doug Skjonsby, age 13, of Florence, Oregon, for his question:

What causes the earth to rotate?

The best brains of science cannot give a complete answer to this question. The earth rotates according to the Newtonian laws of motion, and experts have figures out its rotation to the finest fraction. But this spinning began when the earth was young and nobody can say what caused it.

Young Isaac Newton was interested in traffic laws in a very big way. As a student, he pondered the great cosmic laws that govern the motions of the heavenly bodies the traffic rules obeyed by the starry population of the heavens. He was, of course, a mathematical genius and finally he figured out the basic laws of the cosmos. What's more important to us, he stated these universal laws in simple, understandable language. This was 300 years ago and Newton's laws are still in effect.

Newton's First Law of Motion explains why the earth continues to spin around its axis as it orbits the sun. This law states that a body in motion tends to remain in motion unless acted upon by some outside force. In other words, a moving object keeps going until something else makes it slow down, change its path or stop. That term "outside force" is a sneaky one. It may be the gravity that pulls down falling stones, arrows and flying baseballs. It may be a collision with another object. It may be the Coriolis Force that causes the planetary winds to veer along their paths.

But the earth is out in space and these particular outside forces do not act upon , its motions. It is in an unhampered state of inertia, which is why the First Law of Motion is also called the. Law of Inertia. The earth's rotation continues because nothing. occurs to stop it. Scientists suspect that it once rotated somewhat faster and perhaps the lunar tides are having a very slight slowing effect on its spinning motion. But unless some far greater outside force intervenes, the earth must continue to rotate as it is doing.

This explains what causes the earth's rotation to continue. But, naturally, you wand to know more. Our planet has been spinning since its youth and you wonder what caused this rotation to start. You are not alone. This part of the question has been pondered by every thoughtful young student since Newton. At present, the problem is unsolved and our scientists cannot explain what originally caused the earth to start spinning. That basic quest will, no doubt, by some Newton type thinker of the future. Who knows, earth's rotation  for he just might be a science student, pondering this problem right now in your own school.

Rotation is stylish in the heavens. The sun, the planets and moons of the Solar System all spin around like dizzy dancers. So far as we know, the stars and other major bodies also rotate and the Law of Inertia keeps them spinning in a heavenly hoedown. Since so many heavenly bodies rotate, perhaps the explanation of how rotation began lies in some grand, still to be discovered cosmic law.

Although scientists do not have a conclusive explanation of the original cause of rotation, they have come up with some suggestions. One of these educated guesses relates to other educated guesses about the birth of the earth. If the earth began as a ball of gases and if its gases began to whirl, vortices may have formed. A violently whirling vortex tends to form a central vacuum. A vacuum tends to suck in surrounding particles. These forces may or may not have caused the infant earth to start spinning  but nobody at this time can prove the theory true or false.