1. CONCEPTUAL PHYSICS
Satellite Motion

2. Earth Satellites
An earth satellite is a projectile that falls around Earth rather than into it.
It has to have a tangential velocity fast enough to make its curved path match the curvature of the Earth.
Earth’s curvature drops a vertical distance of 4.9m every 8000m.
If you throw a projectile at a horizontal velocity of 8km/s(29000 km/h), then it would follow the curvature of the Earth.
Orbital speed for close orbit to Earth is 8km/s. But, at this atmospheric friction would burn it. Thus, satellite must stay at about 150km above Earth’s surface.

3. Circular Orbits Elliptical Orbits
In circular orbit, the speed of a satellite is not changed by gravity.
For a satellite close to Earth, the time for a complete orbit about Earth, called the period, is about 90 minutes. For higher altitudes it is longer.
Elliptical Orbits
If a projectile is given a horizontal speed greater than 8km/s, it will overshoot a circular path and trace an oval shaped path called an ellipse.
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4. Energy conservation and satellite motion
A satellite’s speed varies in an elliptical orbit. As it moves away from Earth it looses speed until it reaches a point where it no longer recedes and falls back to Earth and it regains its initial speed. (fig 12.9 p167)
Energy conservation and satellite motion
In circular orbit, the Kinetic Energy and Potential Energy is always constant, thus the speed is constant.
In an elliptical orbit, speed and distance vary.
Potential energy is greatest the farthest away (the apogee) and least when the satellite is the closest (the perigee)
At every point, the sum of potential energy and kinetic energy is the same.
Satellites - Elliptical Orbits

5. Escape speed “ What goes up must come down”
What vertical speed is sufficient enough to insure that what goes up will escape and not come down?
The answer is a speed greater than 11.2km/s.
Read Escape speed p 170
v=  (2GM/d)
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6. What is the escape speed for the moon if its mass=7
What is the escape speed for the moon if its mass=7.35x1022 kg and its radius (d)= 1.74x106 m?
How fast would the moon need to travel to escape the gravitational pull of the Earth, if Earth has a mass of 5.98x1024 kg and the distance from the Earth and the moon is 3.84x108 m?

7. CONCEPTUAL PHYSICS
Satellite Motion