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The Question
(Submitted April 19, 1997)
Do the laws of motion apply in space. Why is it that when in a space shuttle
with no gravity, the people in the shuttle move with the shuttle?
The Answer
Yes, the laws of motion do apply in space. When the shuttle is
launched it is maneuvered into a low Earth orbit-it is orbiting once
around the Earth about every 90 minutes. It is following Newton's laws
in that orbit around the Earth, just as all other Earth satellites,
including the Moon, do. The period of the orbit squared is proportional
to it's orbital semi-major axis (it's distance from the center of mass of the
system) cubed. Geosynchronous (one orbit a day) satellites are therefore
in a higher Earth orbit, while the Moon is still further from Earth.
The shuttle and the astronauts are still gravitationally bound to
the Earth, or they would not orbit. So it is not correct to think of the
shuttle with "no gravity". The shuttle, the astronauts, and any equipment
they have out are all orbiting the Earth in the same orbit, so the astronauts
do not feel gravitationally bound to the shuttle, though they are still
gravitationally bound to the Earth. This is why they float freely within
the shuttle, and why they move with the shuttle.
Regards,
Padi Boyd,
for the "Ask a High-Energy Astronomer Team"
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