|
|
|
| |
Purpose:
To investigate satellite motion.
Background:
Satellites stay in orbit using two forces: the force of gravity and centrifugal force. Gravity pulls the satellite down to earth. Centrifugal force is the outward force on an object caused by its rotation around another object. It's the same force that pushes laundry in a washing machine against the sides during the "spin" cycle. Gravity pulls one way and centripetal pulls the other. The net result is no force on the satellite.
Materials:
Ball-point pen
3-foot wooden ruler
Tape
6 feet of string
Rubber band
Two rubber balls
Metronome
Procedure:
1. Take the pen apart removing the ink cartridge.
2. Tape the pen barrel to one end of the ruler, and run the piece of string through the barrel of the pen.
3. Tie the rubber band to one end of the string.
4. Attach one rubber ball to the end of string.
5. Hold the apparatus in your right hand and swing the rubber ball around above your head. Because the stretch of the rubber band alters the orbit, keep the knot joining the string and the rubber band on the same mark on the ruler at all times.
6. Keep the orbital speed constant by adjusting of the ball until it passes exactly the same point with every tick of the metronome. The orbital speed is the number of revolutions the ball makes per second.
7. Measure how much the rubber band stretches (the satellite's centripetal force) when the orbit speed is kept constant.
8. Measure the stretch when the orbital speed is twice as fast.
9. Attach the second rubber ball and measure the stretch if the orbital speed is the same as in Step #7; then in Step #8.
10. Remove the second rubber ball and cut the string in half. Measure the stretch with one ball and the same orbital speed as in #7. Repeat steps #8 and #9 using the shorter string.
Follow-Up Discussion:
What is the effect on the centripetal force when the mass is doubled and the speed and distance are held constant? What is the effect on the force when the distance is halved and the speed and the mass are held constant? What is the effect on force when the speed is doubled and the distance and mass are held constant?
This activity has been adapted from Space Science Projects for Young Scientists by David McKay and Bruce Smith (Franklin Watts, NY, 1986; ISBN 0-531-15134-4). The book has 8 chapters filled with wonderful experiments and background information covering conditions in space and materials science.