Air, though invisible, has substance. Because of this, our atmosphere exerts considerable pressure at earth's surface—of course, not as great as does the ocean, because air is not as heavy as water. However, air has weight, as is demonstrated by the fact that a helium-filled balloon rises. Helium being lighter than air, the air pushes it up, just as a bubble is pushed up in a glass of water. The average air pressure at sea level is about fifteen pounds (about seven kilograms) per square inch (6.5 square centimeters). At higher altitudes it becomes less dense, therefore lighter. But our "ocean" of air is so extensive that it weighs more than 5,000,000,000,000,000 (five quadrillion) tons.
This air weight means that, at sea level, there is a load of about a ton across your shoulders. But you do not notice it because pressure is pushing in equally on all sides of your body. To offset this outside compression the body maintains an internal pressure, just as the bodies of sea animals have an internal pressure to equalize the tremendous outside pressure from the water surrounding them. This internal pressure that humans have when "at home" in earth's atmosphere makes it necessary for them to wear pressurized suits when they are "away from home" in space. Otherwise, in the near vacuum of outer space, lungs and blood vessels would be ruptured.
This air weight means that, at sea level, there is a load of about a ton across your shoulders. But you do not notice it because pressure is pushing in equally on all sides of your body. To offset this outside compression the body maintains an internal pressure, just as the bodies of sea animals have an internal pressure to equalize the tremendous outside pressure from the water surrounding them. This internal pressure that humans have when "at home" in earth's atmosphere makes it necessary for them to wear pressurized suits when they are "away from home" in space. Otherwise, in the near vacuum of outer space, lungs and blood vessels would be ruptured.
