Orbit

Now what exactly makes an orbit tick?

Imagine you put a gun on top of a mountain and fire in a horizontal direction. The gravitational pull of the Earth would pull the bullet down towards the ground and, after having travelled a certain distance, the bullet will finally strike the ground.

Now as we increase the muzzle velocity, the bullet will travel farther and at a certain speed. The curvature caused by the gravitational pull of the Earth, which pulls the bullet down, will exactly match the curvature of the Earth. The bullet will then keep on flying around the Earth and will fall and fall, never being able to reach the surface of the Earth until it finally hits the breech of the gun from the rear.

This is an orbit.

You can establish such orbits at various altitudes.

Theoretically you could establish one immediately above the ground. But, of course, interference with the atmosphere would slow the bullet down and the orbit wouldn’t be stable.

So we have to go outside of the atmosphere.

But once we are outside of the atmosphere, we have a free choice of any altitude we want.

And the higher we go, the slower will be the velocity required to balance the gravitational pull of the Earth.

For it is the centrifugal force in a curve orbit that cancels the gravitational pull of the Earth and keeps the object in its stable orbit.