The right velocity makes continuous freefall.
The idea of a constant state of freefall may be hard to imagine at first.
- Begin by picturing what would happen if the shuttle had no horizontal velocity...it would simply accelerate to the ground.
- If it had a little horizontal velocity, (give it some by pressing the up arrow) it would move forward as it fell but would still hit the ground.
- With a little more horizontal velocity it would move farther before running into the earth.
- With just the right amount of horizontal velocity it would fall toward the earth but at the same time it would miss hitting the earth. This constant state of freefall is what gives the astronauts an illusion of weightlessness.
- Increasing the horizontal velocity even more would result in an elliptical orbit similar to that of a comet.
Notice that in all cases, the vertical acceleration is approximately 9.8m/s2 toward the center of the Earth. Only in the case of the eccentric elliptical orbit does the distance between the earth and the shuttle become large enough to dramatically reduce the acceleration due to gravity.
 |
 |
 |
