EFFECTS OF WEIGHTLESSNESS

BIOMEDICAL EFFECTS
The Space Shuttle continues in a state of constant free fall until it maneuvers back to Earth. This free fall is the source of the "apparent weightlessness" which astronauts experience in orbit.
Some of the very real effects of this "apparent weightlessness" include:
1. Loss of bone mass (similar to osteoporosis)
2. Reduced total blood volume, particularly loss of red blood cells
3. Giddy, light-headed feeling
4. Space sickness with nausea and vomiting
5. Decrease of heart size
6. Nasal congestion
7. Muscle weakness
Note that the heart does not have to work as hard in space to pump blood. On the other hand, the heart must work hard on the ground because it must pump blood against the force of gravity.
Similarly, muscles do not need to work as hard in space due to the apparent lack of gravity.
Astronauts can maintain healthy muscles in space by exercising. For example, astronauts aboard MIR exercise using a treadmill and stationary bike.
Another effect that astronauts may experience is possible tissue damage from radiation. There is no atmosphere or ozone layer to protect the astronauts from this radiation.
PHYSICS
There are two types of weight:
1. True weight
2. Apparent weight
"True weight" results from Newton's law of gravitation.
The force F between any two particles having masses m1 and m2 separated by a distance r is an attraction acting along the line joining the particles. This force has the magnitude
F = G (m1)(m2)/ (r^2)
where G is a universal constant having the same value for all pairs of particles.
G=6.6720 [10^(-11)] N m^2/kg^2
Reference: Halliday & Resnick, Physics Parts 1 & 2, Wiley, New York, 1978.
A particle can be a planet, a star, a person standing on a planet, or any physical object whatsoever.
The formula for the true weight W can be derived from the Newton formula:
W = mg
where m is the object's mass and g is the acceleration of gravity. The acceleration of gravity at the Earth's surface is about 9.81 meters/sec^2. Again, the "true weight" does not depend on an object's state of rest or motion.
"Apparent weight" is essentially the weight measured by placing the object on a bathroom-type weight scale. Imagine that you were standing on a weight scale inside an elevator. The scale would show that your "apparent weight" increases as the elevator accelerates upward. On the other hand, your "apparent weight" would decrease as the elevator accelerates downward.
An object in a free-fall has "zero apparent weight."
Space shuttle astronauts experience "apparent weightlessness" as the shuttle orbits the Earth. Nevertheless, this "apparent" condition produces very real physiological effects, such as loss of bone mass.
Space shuttle astronauts cannot use a bathroom scale to measure their weight. William Pogue was an astronaut on the Skylab space station. He wrote that this space station had a special chair that swung back and forth on springs. This device was called the body mass measurement device (BMMD).
The mass of the person sitting in the chair could be calculated from the period of oscillation. The period is the time required for one complete cycle of back-and-forth motion.
The person's "true weight" could then be calculated by multiplying mass by the gravitational acceleration.
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Please send comments and questions to Tom Irvine at: tomirvine@aol.com
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