Table of Contents

A Guide to Microgravity for All Ages

Continuous Free Fall

Why doesn't the shuttle hit the ground? The shuttle is in continuous free fall or orbit. It is falling around the earth perpetually.

Continuous free fall means that something is always falling without hitting the earth. When you throw a ball, the earth's gravity pulls it down. While it is in flight it is in free fall. The faster you throw it the farther it goes before coming down and the longer the period of free fall or weightlessness it experiences.

The ball's trajectory when it leaves your hand is a straight line, but gravity pulls on the ball to create a curved path. The faster you throw something, the less curved its path will be and it will go farther before hitting the ground. Bullets fly faster with straighter paths, so they take longer to hit the ground. Throw something fast enough, and eventually its curvature will be the same as the earth's -- it will go all the way around the earth. This is called orbit. The space shuttle and satellites are in orbit around the earth; they are falling freely around the earth.