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Satellites
What keeps them in orbit?
Satellites
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A satellite is any projectile given a
large enough velocity so its path
follows the curvature of the earth.
How fast is the earth moving?
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The earth moves 8000 m in the “X”
direction and 4.9 m in the “Y” direction
every second.
Therefore, if a projectile moves equal
or greater than that speed it will follow
the curvature of the earth (it will never
collide with earth)
Satellite in Orbit
(cannonball example)
What makes a satellite go?
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All objects in circular motion must have an
applied force (usually thrust force).
The centripetal force (inward force) acting
on a satellite is gravity.
Gravity pulls any satellite towards the center
of the earth.
Gravity must equal applied force in order for
satellites to orbit
What happens if its less? greater?
Facts about satellites

As the distance from earth increase:

Radius increase
Force of gravity decreases
Acceleration decreases

Result = required velocity is less

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Satellite problem constants
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Radius of the earth = 6.38 x 106 m
Mass of the earth = 5.97 x 1024 kg
Remember…the radius of a satellite is
the height above the surface of the
earth plus the radius of the earth.
Satellites
d = distance above Earth
+ radius of Earth
Use meters!
Satellite Practice Problems #1

Find the altitude of a satellite orbiting
earth if it is moving at 6,900 m/s and
the pull of gravity is 5.69 m/s2
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Answer: a = v2
r
Solve for “r”
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Satellite Practice Problems #1
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R = (6,900 m/s)2
5.69 m/s2
R = 8.4 x 106 m - 6.38 x 106 m
R = 2.02 x 106 m
Satellite Practice Problems #2
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Find the velocity needed to keep a
satellite orbiting if it is accelerating at a
rate of 8.2 m/s2 and it is 5.00 E5 m
above the surface of the earth.
Answer: a = v2
r
v2 = a x r …v = (sqrt)8.2 x 6.87 E6 m
v = 7500 m/s