Inertial Reference Frame

CORE DEFINITION

In classical physics and special relativity, an inertial frame of reference, or inertial coordinate system, often simply called an inertial frame, is a reference frame in which space can be described uniformly and isotropically, and time can be described uniformly. Within an inertial frame, the physical laws governing the system are independent of external factors. All inertial frames are in uniform translational motion relative to each other. Measurements in different inertial frames can be transformed into each other through simple transformations (Galilean transformation or Lorentz transformation). In general relativity, in any region small enough that spacetime curvature and tidal forces can be neglected, one can find a set of inertial frames to approximately describe the region. In general relativity, systems in non-inertial frames are not affected by external influences due to the principle of geodesic motion. Physical laws take the same form in all inertial frames. In classical physics and special relativity, in non-inertial frames, the physical laws of a system are affected by the acceleration of the reference frame relative to an inertial frame. In such cases, inertial forces must be considered when analyzing the forces on objects. For example, a falling ball does not fall perfectly straight due to the Earth's rotation.