It was proved long ago that :tit's orbit of the earth is safer than the sturdiest of railroad tracks. The same holds true for the orbits of our sister planets. In fact, our Solar System is a secure and stable unit. Its members are held in their places by two great laws which govern the universe.
The orbiting earth is engaged in a mighty tug of war. The two opposing teams are invisible forces which govern all of the heavenly bodies and keep them in their places. The force of the suns gravity pulls our world towards the sun, just as the earth’s gravity pulls a falling stone to the ground. Centrifugal force pulls the earth in the opposite direction and keeps it from falling into the sun.
You can see the force of gravity at work when you drop a stone and watch it fall. You can see centrifugal force at work when you tie a string on a ball and whirl it around and around your head. If you let go or if the string breaks, the ball will fly farther away from you. This is because a whirling body gathers centrifugal f orco and this energy tends to pull it away from the center of its orbit.
The earth travels its orbit at an average speed of eighteen and a half miles a second and at this speed it builds up a terrific amount of centrifugal force. But the pull of the sun’s gravity on the earth is also terrific. It is powerful enough to match the earth’s centrifugal force. The two opposing teams in the tug of war are exactly equal which is why the earth cannot fall into the sun or fly out beyond its orbit.
The pull of gravity between the earth and the sun depends upon the mass of the two heavenly bodies and the distance between them.
If the distance between them were doubled, the pull would be reduced to a quarter. If less massive, the pull between them would be less.
Centrifugal force depends upon mass and speed. If, orbiting at the same speed, the earth were more massive, its centrifugal pull away from the sun would be greater. If, with the same mass; its orbital speed were slower, its centrifugal pull would be less. But these changes are not likely to occur. The balance between gravity and centrifugal force will remain equal. And the tug of war between them holds the earth safely in space.
Actually, the earth is falling, falling towards the sun. However, it does not fall in a straight line like a dropping stone. It falls around and around its orbit. The pull of the sun twists our globe as it falls around its orbit which is why the earth rotates on its axis.