Steven Thompson, age 10, of Richmond, British Columbia, Canada, for his question:
Where does gravity come from?
Where did the earth come from? Where did its seas and dry land come from, its air and its clouds, it plants and animals? Scientists tell us that in the beginning it was created from tiny fragments in a vast cloud of dusty debris. And every tiny fragment came with its own buil.t¬in quota of gravity. Every stone, every cloud and every speck of dust has its own built in gravity. The whole earth has a larger quota and the gravity of the massive sun is enormous.
Our whole world is made of materials called matter. Its liquid water, its solid rocks and its gaseous air are different forms of matter. The moon is a smaller mass of solid matter. The sun is a huge, massive ball of gaseous matter. All the other planets, moons and stars in the universe are made of matter. And a certain amount of gravity belongs to every speck of matter in the entire universe.
Gravity is a very mysterious force and for thousands of years nobody knew how it really works. Of course they knew that ripe apples fall down from the trees and that huge bolders are heavier than small stones. But they did not know why. Then about 300 years ago, a thought¬ful young man named Isaac Newton figured out the answers. He explained that the mysterious force of gravity pulls things toward the center of the earth which is why stones are heavy and why apples fall down ¬instead of up. Newton also explained how the force of gravity works throughout the universe, keeping the stars and planets in their places.
This mysterious built in force is silent and invisible. It works day and night, ail the time. It is a built in part of all the solid, liquid and gaseous matter in the universe. The force of gravity in every object attracts, or pulls at, every other object and every other object pulls back.
Throughout the universe, the force of gravity comes in helpings of different strengths. Its strength depends on two things mass and distance. Mass is the amount of matter packed into an object. The earth's mass includes all the material in the entire planet. Its built in gravity seems to gull everything toward the center of the globe. Above the surface, it gets weaker with distance.
The earth is 81 times more massive than the smaller moon. Hence the moon has a smaller quota of gravity. And since gravity causes weight, a 90 pound earthling weighs only 15 pounds on the lunar surface. The huge sun is 333,000 times more massive than the earth and its mighty gravity is much stronger.
Naturally, the sun's mighty force of gravity reaches out into space. It grows weaker with distance. But its mysterious, invisible might is strong enough to hold each of its planets in its proper place in the Solar System. The same built in force of gravity that makes apples fall down also holds together our great Galaxy of a hundred million stars.