What does it take to stop the PSA?
By trying this out, you probably noticed that for every thrust you
gave the PSA in one direction, you needed to give the same amount
of thrust in the opposite direction the PSA was moving to make
it stop. Of course, you probably also observed
that you have to apply the opposite thrust at just the right time,
or the PSA will stop in the wrong place. This is more difficult
if the PSA is going faster, so you probably found out that its
easier to control the PSA (and actually faster to reach a target)
if you maneuver
it slowly. This also saves energy. Learn more from this video clip
on [low or
How is thrust on the PSA different than a car?
Hopefully you noticed that thrust is not continuous like holding
down a gas pedal, but happens in short spurts that send a PSA off
in one direction or the other. Once a force is applied to an object,
the object moves at that same speed until another force acts on
it. Learn more from this video clip on Newton's [low or
Why doesn't the PSA stop if pushed in one direction?
On Earth, when you roll a ball, eventually it stops rolling, so you
might be wondering why the PSA doesn't stop when pushed in space.
On Earth, gravity pulls the ball down to the ground, so that it
on the ground as it moves, and this rubbing slows it down until
the ball eventually stops. This is called friction, and it acts
like an opposite force. In microgravity there is very little friction,
so things can float around with only air to slow them down. So
in space, we can see that if there isn't anything to slow you down,
you really will travel in one direction until another force in
the opposite direction stops you. Learn more from this video clip
on [low or
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