Download The Physics of Orbits

The Physics of Orbits
Three of Newton’s Laws combine to
explain why satellites orbit like they
do.
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)
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.
The force that does this is called a Centripetal Force
and the amount needed 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!
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