Learn about the principle of relativity in this video from the American Museum of Natural History. According to Galilean, or Newtonian, relativity, the speeds of moving objects can be added in different inertial frames of reference, as demonstrated in the video by throwing an orange on a moving train. However, for objects traveling near the speed of light, Galilean relativity does not hold. Learn about Einstein's special theory of relativity: how it takes into account that the speed of light is constant for any observer, and how it describes the motion and consequences of objects traveling near the speed of light.