<Table> <Tr> <Td> </Td> <Td> This article's tone or style may not reflect the encyclopedic tone used on Wikipedia . See Wikipedia's guide to writing better articles for suggestions . (January 2018) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article's tone or style may not reflect the encyclopedic tone used on Wikipedia . See Wikipedia's guide to writing better articles for suggestions . (January 2018) (Learn how and when to remove this template message) </Td> </Tr> <P> An inertial frame of reference in classical physics and special relativity is a frame of reference in which a body with zero net force acting upon it is not accelerating; that is, such a body is at rest or it is moving at a constant speed in a straight line . In analytical terms, it is a frame of reference that describes time and space homogeneously, isotropically, and in a time - independent manner . Conceptually, the physics of a system in an inertial frame have no causes external to the system . An inertial frame of reference may also be called an inertial reference frame, inertial frame, Galilean reference frame, or inertial space . </P> <P> All inertial frames are in a state of constant, rectilinear motion with respect to one another; an accelerometer moving with any of them would detect zero acceleration . Measurements in one inertial frame can be converted to measurements in another by a simple transformation (the Galilean transformation in Newtonian physics and the Lorentz transformation in special relativity). In general relativity, in any region small enough for the curvature of spacetime and tidal forces to be negligible, one can find a set of inertial frames that approximately describe that region . </P>

When can an inertial system be also considered a reference system