What makes a satellite fall

That tug toward Earth--combined with the momentum from the rocket… …causes the satellite to follow a circular path around Earth: an orbit. But finding this balance is sort of tricky. Gravity is stronger the closer you are to Earth. And satellites that orbit close to Earth must travel at very high speeds to stay in orbit. This would cause the projectile to stay the same height above the earth and to orbit in a circular path such as path C. And at even greater launch speeds, a cannonball would once more orbit the earth, but now in an elliptical path as in path D.

At every point along its trajectory, a satellite is falling toward the earth. Yet because the earth curves, it never reaches the earth. So what launch speed does a satellite need in order to orbit the earth? The answer emerges from a basic fact about the curvature of the earth. For every meters measured along the horizon of the earth, the earth's surface curves downward by approximately 5 meters.

So if you were to look out horizontally along the horizon of the Earth for meters, you would observe that the Earth curves downwards below this straight-line path a distance of 5 meters.

For a projectile to orbit the earth, it must travel horizontally a distance of meters for every 5 meters of vertical fall. It so happens that the vertical distance that a horizontally launched projectile would fall in its first second is approximately 5 meters 0.

This assumes that it is launched above the surface of the earth and encounters negligible atmospheric drag. As the projectile travels tangentially a distance of meters in 1 second, it will drop approximately 5 meters towards the earth.

Yet, the projectile will remain the same distance above the earth due to the fact that the earth curves at the same rate that the projectile falls. The motion of an orbiting satellite can be described by the same motion characteristics as any object in circular motion.

The velocity of the satellite would be directed tangent to the circle at every point along its path. The acceleration of the satellite would be directed towards the center of the circle - towards the central body that it is orbiting. And this acceleration is caused by a net force that is directed inwards in the same direction as the acceleration.

This centripetal force is supplied by gravity - the force that universally acts at a distance between any two objects that have mass. Were it not for this force, the satellite in motion would continue in motion at the same speed and in the same direction. It would follow its inertial, straight-line path. The heat makes the satellite break into pieces.

Only some pieces survive to fall onto the surface of the Earth, or into the sea. These are often steel fuel tanks or titanium spheres - also called space balls. Sometimes, people find them on the ground many years later. These satellites have heat shields to keep them cool and parachutes to slow them down so that they land softly, still in one piece.

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