Lynn Rumfelt, age 11, of McAdenville, N.C., for her question:

HOW HIGH DOES GRAVITY GO?

Astronomers from ancient Greece studied the motions of the planets and the moon, but it wasn't until the late 1600s that these motions were correctly explained. An English scientist named Isaac Newton showed that there is a connection between the force that attracts objects to the earth and the way the planets move.

Gravitation is the force of attraction that acts between all objects because of their mass  that is, the amount of material they are made of. Gravitation holds the universe together.

Isaac Newton published his theory of gravitation in 1687. He realized that the same force that made an apple fall on earth holds the moon in its orbit around the earth.

In 1915 the German born American scientist Albert Einstein announced his theory of gravitation. Although his theory involved a complete change in the ideas about gravitation, it explains rather than contradicts Newton's theory.

We know that an object's weight on earth  that is, the strength of the gravitational force pulling on it  decreases as the object moves away from the earth. At some point between the earth and the moon, the object is pulled equally by both bodies and, therefore, weighs nothing. The point varies with the distance between the two bodies. The object's weight then increases until it reaches the moon's surface.

So how high does gravity go? An object weighing 16 ounces on earth would weigh only four ounces at an altitude of 8,000 miles. Its weight would drop to 1 ounce at 16,000 miles and one sixteenth of an ounce at 64,000 miles. It would have absolutely no weight at 210,000 miles from earth.

There's less mass on the moon than on earth, so by the time our 16 ounce object reached that distant location 238,857 miles from earth, it would weigh only two and two thirds of an ounce.

That same 16 ounce object would weigh one tenth of an ounce less at the equator that it does at 40 degrees north latitude. And if you weighed it at the North Pole, you'd come up with 16 and a half ounces. The reason for this is that the earth isn't exactly round. If you could bury the object in the exact center of the earth, it would have no weight.

Many scientists today think that a change in a gravitational field may give off gravitational waves. However, these waves  if they do indeed exist ¬would be difficult to detect. An American physicist named Joseph Weber reported some theories on this subject in 1969 but many scientists are demanding additional experiments and study on the subject.