Newton’s Thought Experiment

1. Newton’s Thought Experiment

2. If you throw an object 5 miles/sec. the object will curve downward but if that curve matches the curvature of the earth the object never hits the earth. • The object stays at a constant height above the earth. The object is in orbit.

3. Gravity acts on the moon as well as an apple /www.physics.uc.edu

4. Satellites • The farther from the earth, the less gravitational force there is. The velocity to stay in orbit decreases as objects move away from the earth. • LEO (low earth orbits) satellites are only 100 miles from the surface. • LEO satellites must travel fast at 5 miles/sec. • LEO satellites orbit the earth in 90 minutes.

5. LEO satellites • Travel 100 miles from the surface • Move 300 miles per minute • Radio data to the ground • Often seen after dusk in the night sky

6. Geostationary Earth Orbit • GEO satellites are 22,000 miles from earth where gravitational force is weaker. • GEO satellites can travel slower at 2 miles/sec. • At 2 miles/sec and at a distance of 22,000 from earth it takes one day to orbit the earth. • GEO satellites move with the earth, so they are stationary relative to the earth.

7. GEO satellites • Weather satellites • Satellite TV Receiving antennas do not have to move to stay in contact with GEO satellites.

8. Medium Earth Orbit Satellites • There are 24 GPS satellites that are about 12,000 miles from the earth • Travel 7000 miles/hr, circling the earth twice in less than a day. • The GPS receiver receives signals from three or more GPS satellites. • The time for the signal to be received enables the receiver to calculate distance from the satellite.

9. Triangulation to determine location http://www.gpssystems.org.uk/how-gps-works/

10. Resources • Garmin Website • Physics for Future Presidents, Richard Muller, of UC Berkeley