500
After the shuttle reaches orbit, its engine shut down. But it is still orbiting around the Earth without hitting the Earth. What forces are acting upon it?
Inertia carries the shuttle forward. Gravity causes the shuttle to fall. The shuttle falls continuously toward Earth. But at the same time, it moves forward fast enough to keep from hitting Earth. The curve of the shuttle's path as it moves is the same as the curve of Earth, so the shuttle doesn't get any closer to Earth's surface.