Paul Dixon, age 11, of Wallaceton, PA., for his question:
HOW DOES GRAVITY WORK?
Gravity is the force of attraction that acts between all objects because of their mass. Mass is the amount of material the objects are made of.
The true nature of gravity isn't known but it is presumed to have the nature of electromagnetic propagation. It is a field of force or of attraction that surrounds every material object, no matter how small.
Gravitation holds the universe together. Large objects, like the sun, have gravitational forces so strong that they can hold planets in their orbits even though they are hundreds of millions of miles away.
Smaller objects in space, like the moon, have weaker fields. The moon's gravity is only one sixth that of the earth yet it is strong enough to pull or wrinkle the waters of the earth and cause tides.
The force of gravity doesn't diminish rapidly as you leave the earth.The earth is so big that its attraction does not weaken immediately as youleave the surface. At 200 miles' altitude, gravitation still has 90percent of its ground level strength.
The earth's gravitational force is still reduced to only 50 percent when an object has risen to about 3,000 miles above the surface.
If an object weighing 16 ounces on earth were to travel to the moon, it would weigh four ounces at 8,000 miles, one ounce at 16,000 miles and one sixteenth of an ounce at 64,000 miles. When it reached a distance of 210,000 miles, it would have no weight at all. Higher than that, the moon would start its gravitational pull.
When the 16 ounce object landed on the moon, it would weigh two and two thirds of an ounce. The lower weight, of course, would be due to the fact that the moon's mass was smaller than the earth's and therefore the gravitational force was less.
The ancient Greek astronomers studied the motions of planets and the moon and came up with some theories about gravity. But it wasn't until the late 1600s when an English scientist named Isaac Newton correctly showed that there was a connection between the force that attracts objects to the earth and the way the planets move.
Newton based his explanation on the observations of planetary motions by two astronomers of the late 1500s and early 1600s. Tycho Brahe of Denmark and Johannes Kepler of Germany.
Newton's theory of gravitation says that the gravitational force between two objects is proportional, or related directly, to the size of their mass. The larger the mass, the larger is the force between the two objects.
Albert Einstein's 1916 theory of gravitation involved a complete change in the ideas about gravitation but it explains rather than contradicts Newton's theory.