1. The Physics of Orbits
Three of Newton’s Laws combine to explain why satellites orbit like they do.

2. Newton’s First Law and Orbits
A satellite following Newton’s First Law of motion tends to keep going…
In a Line that is Tangent to the orbit
because they change direction satellites are undergoing acceleration.
This is called Centripetal Acceleration, and it is:
(copy formula)
Toward the center of the orbit

3. Newton’s Second Law and Orbits
According to the second law if satellite is accelerating then there must be a Force that makes it do so.
Called Centripetal Force
It is given by:
(copy formula)
Notice that force must be greater when the velocity is greater or if the turn is sharper
That is…
When the radius is smaller!

4. Orbits and The Universal Law of Gravity
Many things can provide centripetal force.
For satellites in orbit it is Gravity that provides the Centripetal Force.
If “falling” is accelerating due to Gravity
then satellites are falling, but the acceleration changes the direction rather than the speed.
A satellite orbiting Earth is falling.
It just keeps missing the Earth!
Because
the Earth curves away
and the satellite ’s tangential velocity is so great