Mass of Shuttle and Floating Objects
Country: United States
Date: June 2008
Does an object, say a baseball, floating inside the Space
Shuttle, add weight to the shuttle? Even if it is floating and not
When the Space Shuttle is in steady orbit, it HAS almost no weight. Weight is the
sensation of unequal aplication of force--for instance, when you stand on the
ground, the sensation of "weight" is from the ground pushing up on your feet. The
pull of the Earth's gravity on you is on all parts of your body equally; that does
not cause the sensation of weight. When you are in free fall, you feel weightless,
even though gravity pulls on you just as strongly as when you stand on the ground.
When the Space Shuttle is in orbit, gravity pulls on all parts of the Shuttle and
all parts of its contents, floating or not, equally. Since there is no unequal
application of force, there is no sensation of weight. In that sense, no, objects
floating inside the Shuttle do NOT contribute to the Shuttle's weight because
neither they nor the Shuttle have weight.
When it comes to changing the Shuttle's orbit or getting it into orbit in the first
place, all objects inside the Shuttle contribute to its mass. So every baseball
added to the Shuttle makes the Shuttle that much harder to accelerate. When the
shuttle takes off, or when its orbit is being changed, however, it will not be
weightless, because the push from its engines gives it an unequal application of
force just as sitting ion the ground does. When that happens, the baseball will
not be floating. It will pushing against some surface of the Shuttle.
Richard Barrans, Ph.D., M.Ed.
University of Wyoming
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Update: June 2012