William Atkins
Friday, 10 July 2009 20:04
Science -
Health
Page 2 of 5
Many of the medical conditions caused by exposure to weightlessness (the "perceived lack of gravity" in space) are similar to those resulting from aging. Scientists believe that studies of the detrimental effects of weightlessness could have medical benefits, such as a possible treatment for osteoporosis and improved medical care for the bed-ridden and elderly.
Human bones deteriorate quite quickly when in orbit about the Earth because there is nothing for them to push or pull against for resistance. In other words, when we walk on Earth, for instance, gravity is pushing down on our bones, helping them to get some exercise.
When we pick up a pail of water, the weight of the pail filled of water helps to keep our bones and muscles strong. Its weight is caused by the force of gravity (Weight = mass x gravity). The same principle applies when people lift weights for exercise (which is especially important to do throughout one’s life to keep bones and muscles strong).
However, in orbit about Earth, such as when inside the International Space Station, the astronauts do not “feel” the force of gravity (gravity is “perceived” not to be present) because they are essentially in free-fall.
They are almost like a parachutist falling to Earth, except that the forward speed of the Space Station is so fast that it keeps the spacecraft from impacting Earth and, instead, keeps it in an orbit about Earth.
Gravity is still present while in orbit about Earth, only the astronauts cannot perceive it because of their constant state of free-fall around the planet. As a result, their weight is almost zero. (Weight = mass x gravity, mass remains the same but if gravity is perceived to be almost zero then weight will also be almost zero).
NASA states,
“In space, even more than on Earth, it's "use it or lose it." The human body and all its parts need to work to remain vital. Bones must bear weight to keep their density and strength. Muscles need to push or pull against resistance to stay in shape; without work they waste away. Is this also true of our most critical muscle – the human heart?”
Page three continues.
