### Discover how a satellite stays in orbit.

1. Cut a piece of nylon to put around the rubber ball.
2. Tie one end of a 3-foot length of string around the nylon.
3. Hold the other end of the string and begin to whirl the ball over your head.

The ball is held in its "orbit" around your head by the string, which is similar to the force of gravity that pulls satellites toward the Earth.

The forward motion of the ball is its momentum. If the "gravity" of the string were not acting on the ball, the ball would continue in one direction. The swinging of the ball gives it its forward motion. When these two forces are equal, the ball remains in orbit, without falling into or flying away from the Earth (you). A satellite's forward motion is controlled by rockets. When the rockets are not fired, inertia keeps the satellite going in one direction.

1. Discuss other examples of momentum and gravity, for example, swinging a bucket of water over your head without getting drenched; or riding amusement park rides where you turn upside down or in a loop without falling out.
2. Let go of the string.

What happens? (The ball flies outward, since gravity is now equal to zero.)

### Satellites in the News

Find examples of how satellites are used now in communications, weather forecasting, business, and science by clipping relevant articles in magazines and newspapers. Start a satellite bulletin board.

Discuss advantages and disadvantages of using satellites rather than "old" technologies, such as communications satellites compared to telephone wires.

### Satellite Graveyard

Evenutally satellites stop working for various reasons. Depending on the orbit of the satellite one of two things occur. Satellites in low earth orbit will eventually burn up in the Earth's atmosphere. Satellites in geostationary orbit are moved further out into a less desirable orbit.

Discuss why satellites are not brought back to Earth (cost). Consider the analogy to the world's oceans that were once considered a limitless area to discard waste. So you think the same thing will happen to outer space? How can that be avoided?

### Materials

• string
• nylon pantyhose
• small rubber ball