Coriolis field

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In theoretical physics a Coriolis field is the apparent gravitational field felt by a rotating or forcibly-accelerated body.

In a theory that conforms to some versions of Mach's principle, we are entitled to treat this “apparent”, “fictitious” or “pseudo-gravitational” field effect as genuine.

When an object is set down on a rotating children’s roundabout and is seen to slide away from the centre of the roundabout, then as well as using the non-rotating frame as a reference and saying that the outward motion is a consequence of the object’s inertial mass (its tendency to continue moving in a straight line), we can also take the rotating frame as a reference, and say that the object, seen in this frame, is being pulled outwards by a special sort of radial gravitational field caused by the relative rotation of the outside universe, and that its outward motion is instead a consequence of its gravitational mass.

This sort of dual description is used to unify the ideas of inertial and gravitational mass under general theories of relativity, and to explain why an object’s inertial mass and gravitational mass are proportional in classical theory: in these descriptions, the distinction is purely a matter of convenience: inertial and gravitational mass are different ways of describing the same behaviour.

[edit] Is it real?

The idea that the Coriolis field is a real physical effect and not just a mathematical artifact is justified in a Machian theory by saying that evidence of the field’s existence is not only visible to the rotating observer, its distortion is also visible and verifiable for non-rotating onlookers: the relative rotation of the roundabout and universe masses creates a real physical distortion in spacetime that is theoretically visible to all observers (see: Kerr black hole, frame-dragging, light-dragging effects), and the physical consequences of rotation experienced by the rotating-frame observer can be said to be “smudged into” the non-rotating observer’s physics. The Coriolis field can then be claimed to have a genuine existence, it is expressed in the intrinsic curvature of the region and cannot be made to vanish with a convenient mathematical change of coordinate system. The forces and effects are mutual – the roundabout observer feels the outside universe pulling more strongly along the rotation plane, and pulling matter around, and (to a far lesser extent) the mass of the rotating roundabout creates a stronger inward pull and pulls matter around with it, too.

In this way, general theories of relativity are supposed to also eliminate the strict distinction between inertial and noninertial frames: if we take an inertial observer in flat spacetime and have them observe a rotating disc, the existence of the rotating mass means that spacetime is no longer flat, and that the concept of rotation is now subject to the democratic principle.

This elimination of the concept of the inertial frame was initially described by Einstein as one of the great successes of his general theory of relativity.