William Goral, age 10, of Brookfield, Wis,',, for his question:
What makes the earth spin as it orbits the sun?
Around and around and away we go, whether we like it or not, for our dizzy old world is whirling and waltzing around in several different directions at the same time, and we must go along with the whirligig. One of its planetary motions takes us spinning around like a top.
Our earth is a born traveler, and scientists suspect that its cosmic whirligig began at the beginning. The young planet most likely was orbiting the sun and spinning on its axis when or soon after it was formed. The yearly orbit is its revolution, the daily spin is its rotation, and the earths revolution and rotation are related to each other. Both move in an easterly direction and are governed by cosmic laws that direct the motions of heavenly bodies.
Perhaps the ymung planet planned to travel in a straight line thrcugh empty space without rotating. It has enough speed energy to do this., but such a space trip is possible only under conditions of complete nothingness: and our planet is far from alone in the heavens. Its own speed carried it away, and the gravitation of the mighty sun pulled it back. At a certain point these two opposing forces balanced each other, and the earth fell in a curved orbit around the sun.
A globe can travel along without spinning when no other influences are exerted upon it, and many dynamic influences are exerted upon our planet. Its weight is not evenly distributed, and this adds a roly poly turn to its motion as it falls around the sun. Its speed is dragged by heavy air masses, the weight of meteor dust and tidal friction from the moon. Its daily rotation is speeded and slowed by other factors which we do not yet understand.
The earth was born with enough speed to travel forever and was forced into a curved path around the sun. The balance of the orbiting globe was upset by its weight and mass, by the moon and other factors, and it had to rotate. It rolled forward toward, the east, in the same direction it falls around the sun.
Reliable man made clocks show that the daily rotations grow longer each century by 0.0016 seconds so that we gain about 3.5 extra hours in 2,000 years. In spring the rotation speed is 0.001 seconds longer and in fall 0.001 seconds shorter than average. And during a few centuries, unknown factors cause it to vary as much as 30 seconds.