We make use of what is called the "sling shot
effect" to increase the speed and redirect the
motion of a satellite bound for distant
planets.When the planets are in just the right
positions in their orbits, their momentum can be
used to accelerate a satellite, giving it much
greater velocity than its original rocket booster.
It works this way.
The satellite and the
planet both have mass and therefore gravity.
They both pull on each other with equal force.
Each also has a velocity (speed and direction)
and momentum (the tendancy to keep moving in its
current direction). If we aim the satellite so it
passes just behind the planet as the planet moves
in its orbit "around" the Sun, the planet will
pull on the satellite, and the satellite will pull
on the planet. The result is that the planet will
slow down in its orbit just the very tiniest
amount, and the satellite will speed up a lot and
go in a different direction. The satellite's path
will bend slightly towards the direction the
planet is moving. In keeping with the law of
conservation of momentum, the planet gives up a
little of its momentum to the satellite, which
then speeds off to a distant
You can experience the same
sort of thing on a basketball court. If you run
with the ball, then throw it ahead of you, can you
sense your speed decreasing as you release the
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