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Encyclopedia > Inertial

In physics, an inertial frame of reference, or inertial frame for short (also descibed as absolute frame of reference), is a frame of reference in which the observers move without the influence of any accelerating or decelerating force. The term "inertia" refers to a direction through spacetime, and "frame" defines an area wherein the inertia is functionally the same for the relevant observers.

The inertial frame is a space-time coordinate system that neither rotates nor accelerates. Different inertial reference frames may have different origins at any given moment in time, and their origins may be moving at constant speed and direction relative to each other. A non-inertial frame of reference is a coordinate system which is accelerating. The transformation from one inertial frame of reference to another is done using Lorentz transformations, or, at speeds considerably below the speed of light, Galilean transformations.

The term is used in cases where relativity is considered, and a meaningful difference is drawn between the views of two observers with respect to their time and space intervals. From within the same inertial frame of reference, functions of relativity can be adequately replaced by classical mechanics. The above transfomations are applied for scaling upward from the local frame to larger frames, and for backwards verification of general theories back to the observable local frame.

The frame concept is at the core of the questions dealing how the apparent classical mechanics of particular inertial frame relates to the general theories of the universe and spacetime. By the very nature of human limits to a particular inertial frame, the various branches of physics are devoted to building functions that relate human observation to theoretical concepts of cosmology and quantum mechanics and the rules by which they interoperate to describe possible reference frames like our own.

Inertial frames of reference appear prominently in both Newtonian relativity and Einstein's special theory of relativity. In Newtonian mechanics, any mass viewed from an inertial reference frame will appear either to be stationary or to be moving at constant speed in a straight line, if and only if the sum of forces acting upon that mass is zero. (This is also known as Newton's first law of motion.)

Frames of reference are purely theoretical, because gravitational force (and thus acceleration) exists everywhere in the known universe. However, they may be approximated very well in intergalactic space, or to a lesser extent within the confines of a coasting spacecraft. If you can find an inertial frame of reference for a given situation, then it can always be transformed by a change of coordinates into one in which the observers do not move at all.

Results from FactBites:

 CGA FAQ: Centrifugal force & inertial frames (3784 words) Even though it is true that the solution would be the same when the equations are solved in an inertial frame, one can imagine the difficulties when weather forecasting would be done on a mesh attached to the sun, or the galaxy, or the center of mass of the universe... Let R be a rotation matrix describing the orientation of the moving reference frame relative to the inertial reference frame, and Ao be the acceleration of the origin of the moving reference frame measured in the inertial reference frame. The inertial frame used by the > accelerometers is, of course, tilted relative to the usual horizontal and > vertical axes of the frame attached to the earth, and its > orientation changes with time.
 UCB Inertial Fusion Energy Tutorial (3235 words) This claim about the potential economic viability of inertial fusion energy is certainly a strong one, but several inherent characteristics of ICF technology support this viewpoint. In inertial confinement fusion, small B-B-size hollow spherical capsules, most likely made of plastic, are filled at high pressure with an equal mixture of deuterium and tritium, and then chilled to cryogenic temperatures, so that the D-T gas freezes as a thin, solid coating on the inside of the capsule wall. The chapter "The Economics of IFE" discusses the economic characteristics of inertial fusion energy development that make IFE an attractive candidate for research and development investment, particularly when the scientific feasibility of ignition is demonstrated experimentally at the National Ignition Facility.
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