## GRAVITY

 Strength of gravity is usually expressed by "g" units. "1g" is equal to the same force of gravity like earth. 0.5 g means half the force of earth's gravity. Thus if you weighed 60 kg on earth you would weigh 30 kg in a 0.5 g environment, and 120 kg in a 2 g environment.. Although a few individuals have lived in 0g for up to a year or so, raising children in 0g will be unacceptable for quite some time, perhaps forever. Children raised in 0 g, or even low-g, would not be able to visit Earth without severe discomfort because their muscles and bones would not be adapted to our gravity field. Children raised in 0 g would probably have very weak bones and muscles. For this reason, any colony must have pseudo-gravity. This can be accomplished by rotation or by very long tethers. Gravity is a force generated by large amounts of mass (for example Earth). A force that is similar to gravity can also be generated by changing velocity, either its magnitude (speed) or direction. While driving a car, if you try to stop it suddenly you will feel a force pushing you forward. If you change the direction of the car suddenly, by taking a sharp turn you can also see the force generated when things on dashboard begins to slide. Amusement park rides take advantage of the "pseudo-gravity" generated by rotation (changing the direction of the velocity continously).

The larger the radius of the colony, the slower the rotation rate necessary to achieve 1g of pseudogravity. Very fast rotation rates necessary for small colony radii generate strong coriolis forces on the inhabitants. No one knows the maximum acceptable rotation rate, but most people believe 1 or perhaps 2 rotations per minute (rpm) to be the maximum . This corresponds to a colony radius of about 1000 to 250 meters. The equation relating force to radius and rotation rate is a = w w r, where a is the acceleration due to "pseudo-gravity", r is the rotation radius of the colony, and w is the rotation rate in rad/sec.
See animations for
• Dumbbell
• Cylinder
• Torus