Inertial frame of reference

In classical physics and special relativity, an inertial frame of reference (also called inertial space, or Galilean reference frame) is a frame of reference not undergoing any acceleration. It is a frame in which an isolated physical object—an object with zero net force acting on it—is perceived to move with a constant velocity or, equivalently, it is a frame of reference in which Newton's first law of motion holds.[1] All inertial frames are in a state of constant, rectilinear motion (straight line motion) with respect to one another; in other words, an accelerometer moving with any of them would detect zero acceleration.

Measurements of objects in motion (but not subject to forces) in one inertial frame can be converted to measurements in another by a simple transformation - the Galilean transformation in Newtonian physics or by using the Lorentz transformation (combined with a translation) in special relativity[2] when the relative speed of the frames is more than about 10% of the speed of light.

In classical mechanics, for example, a ball dropped towards the ground does not move exactly straight down because the Earth is rotating. This means the frame of reference of an observer on Earth is not inertial. As a consequence, the Coriolis effect—an apparent force— must be taken into account to predict the respective small horizontal motion. Another example of an apparent force appearing in rotating reference frames concerns the centrifugal effect, the centrifugal force.

In a non-inertial reference frame, viewed from a classical physics and special relativity perspective, the interactions between the fundamental constituents of the observable universe (the physics of a system) vary depending on the acceleration of that frame with respect to an inertial frame. Viewed from this perspective and due to the phenomenon of inertia, the 'usual' physical forces between two bodies have to be supplemented by apparently sourceless inertial forces.[3][4] Viewed from a general relativity theory perspective, appearing inertial forces (the supplementary external causes) are attributed to geodesic motion in spacetime.

  1. ^ Fields, Douglas E. (Spring 2020). "Lecture25: Galilean and Special Relativity" (PDF). PHYC 2310: Calculus Based Physics III. University of New Mexico. p. 8. Retrieved 7 November 2020.
  2. ^ Puebe, Jean-Laurent (2009). Fluid Mechanics. John Wiley & Sons. p. 62. ISBN 978-1-84821-065-3.
  3. ^ Milton A. Rothman (1989). Discovering the Natural Laws: The Experimental Basis of Physics. Courier Dover Publications. p. 23-24. ISBN 0-486-26178-6. reference laws of physics.
  4. ^ Sidney Borowitz; Lawrence A. Bornstein (1968). A Contemporary View of Elementary Physics. McGraw-Hill. p. 138. ASIN B000GQB02A.

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