# How do space ships make artificial gravity?

Category: Space
Published: February 14, 2013

By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and physics professor at West Texas A&M University

Despite the fact that outer space is brimming with gravity, the lack of solid ground in space means that objects without thrust are in a continual state of free fall, and free fall feels just like zero gravity. To stop all objects in a space ship from floating around due to their free fall motion, you would need artifical gravity. In the conventional sense, artificial gravity connotes a system aboard a ship that makes all objects fall to the floor and be held there as if they were on earth's surface, but still allows people to walk around freely. In this sense, straps my hold a weightless astronaut to the floor, but they would not quality as artificial gravity because they would not allow the astronaut to walk around. Similarly, magnetic belts would not quality as artificial gravity because objects that the astronaut releases would still float around.

The only physically possible way to create a force as strong as earth's gravity that acts on all objects in a ship is through acceleration. Acceleration always creates inertial forces. Inertial forces such as the centrifugal force or Coriolis force are very real in the accelerating reference frame. They are not imaginary or fictional, but are simply non-fundamental in that they arise from the movement of the frame itself. If the acceleration is held constant and at the right value, the inertial force will behave identically to earth's gravity and will, in fact, be equivalent to earth's gravity. This fact is actually a basic tenet of General Relativity. There are two kinds of accelerations, rotational and linear. A ship could achieve artificial gravity by rotating about its axis. To be practical, the radius of rotation would have to be quite large. Additionally, a ship could create artificial gravity by constantly accelerating forwards. Shows that portray artificial gravity without rotation or constant forward acceleration are simply non-physical. Incorrect artificial gravity is often used in movies because of budgeting concerns. It is very expensive to make actors sitting on earth look like space voyagers floating in a space ship, or alternatively, to construct a space ship set that is constantly rotating.