Bobbie Grabber, age 6, of Milford, Conn, for question:
Why doesn't the moon fall from the sky?
In days gone by, children were told that the moon was a slice of green cheese. Of course, even then the people knew that things tend to fall down when they are not held up. But nobody worried much whether the moon would fall down or wondered why it didn't, After all, if it were made of green cheese, it could do no harm if it did fall.
Nowadays we all know that the moon is not made of green cheese. It is a huge round ball eighty one moans would be as big as the whole world. It has mountains and jagged holes all over its surface.
We know that things tend to fall to the ground. So we wonder why I this great ball doesn't come crashing down and if not, why not.
There is no need at all to worry about this. The moon will not come crashing down, and that is certain.
Things fall because the great force of gravitation pulls them toward the very center of the earth. Everything is held to the ground by this mighty force. However, gravitation loses its force as It gets further from the center of the earth, The pull of gravity is not so strong on the air for above as it is on the dense atmosphere close to the ground.
Higher up, further out from the center of the earth, is the moon. It feels the gull of earth's gravitation, but not nearly so strongly as we do on the ground. It feels the mighty pull strongly enough, however, to be unable to tear itself away and drift off into space. The pull of earth’s gravity holds the moon strongly enough to keep it forever in its orbit about 233,000 miles away.
That, of course, does not explain why the moon does not come tumbling nearer and nearer to the earth, It only explains why the moon stays with us. Actually the moon has no intention of coming any nearer to the earth, And it has a force of its own to keep it at a safe distance.
Maybe you have whirled a ball on a string around your head. At dust the right speed, the ball seems to circle around with hardly any help from you. Too slow, and it begins to sag. Too fast, and the whirling ball may pull hard enough to break the string and fly away. This is because all whirling objects tend to null away from the center of the circle they make. In fact, there is a strong force pushing them to the outer ring of the circle.
The moon is whirling at a safe distance from the earth because it is kept there by this same force which kept the whirling ball swinging outwards. This is called by the long name of centrifugal force. The circling moon has enough centrifugal force to keep it from falling to earth. The earth has enough gravitation to keep it from floating away.
The moon is kept in place because these two great forces exactly balance each other. They are at work all year round and every day and night of the week. And they need no help from us at all. In fact there is nothing we could do to help or hinder them. Our beautiful moon is very safe up there in the sky.