Newton's Third Law of Motion: Astronauts in Outer Space

http://www.myspace.com/acorvettes NASA scientists and engineers should probably have predicted that if an astronaut applied force to open or close a valve, the valve would apply the same amount of force to him, but in the opposite direction. After all, nearly 300 years ago, Isaac Newton presented what came to be known as his third law of motion, which says that for every action there is an equal and opposite reaction. We experience these conditions on Earth; if we lean heavily against a wall, the wall pushes back with a force equal and opposite to our lean. (To illustrate the wall's opposing force more vividly, imagine leaning against it while wearing roller skates.) On Earth, gravity and friction provide the stability we need to resist the forces exerted on us during everyday tasks. In contrast, orbiting astronauts must struggle against conditions of "weightlessness."