Jeffery Stepp, age 13, of High Point, North Carolina, for his question:

Is it true that things weigh less at the equator?

This problem relates to the law of gravity. The strength of this mysterious force depends upon a planet's mass and reaches outward in all directions from the center of its mass. The earth's center of gravity is in the middle of its heavy core. Its pulling force gives weight to objects on the surface of the planet. The weight of a two pound brick is the measure of the force of gravity exerted upon it at a certain distance from the earth's center of gravity.

Distance is an important factor because the force of gravity diminishes as we get farther from the center of the planet's mass. On the earth's surface, the center of gravity is somewhat less than 4,000 miles straight down beneath our feet. But the earth is not a perfect sphere. It bulges a trifle at the equator. Here we are roughly 13 1/2 miles farther from the center of gravity than when standing on top of the South Pole. The earth's gravity does not lose much of its pulling power in this short distance of 13 1/2 miles    but it does lose a little. Hence, at the equator a person weighs a trifle less than at the poles, though the difference is not enough to make him feel any lighter.