# Inertial Frame of Reference

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## Inertial Frame of Reference

a frame of reference in which the law of inertia is valid: a mass point is at a state of rest or uniform linear motion when it is not acted on by any forces (or when it is acted on by balanced forces). Any frame of reference that is moving translationally, uniformly, and rectilinearly with respect to an inertial frame of reference is also an inertial frame of reference. Consequently, in theory any number of fully valid inertial frames of reference may exist with the important property that in all such frames the laws of physics are identical (the so-called relativity principle). In addition to the law of inertia, in any inertial frame of reference Newton’s second law and the laws of conservation of momentum and of angular momentum, as well as the law of motion of the center of inertia (or center of mass), are also valid for closed systems (systems not subject to external influences).

If a frame of reference does not move uniformly and linearly with respect to an inertial frame of reference, it is a noninertial frame, and neither the law of inertia nor the other laws mentioned above are observed within it. This is because even in the absence of acting forces a mass point will have an acceleration with respect to a noninertial frame of reference as a result of the accelerated translatory or rotational motion of the frame of reference itself.

The concept of an inertial frame of reference is a scientific abstraction. A real frame of reference is always connected with some specific body, such as the earth or the body of a ship or aircraft, with respect to which the motion of various objects is studied. Since there are no stationary bodies in nature (a body that is stationary with respect to the earth will move together with it under acceleration with respect to the sun and stars), any real frame of reference may be considered as an inertial frame of reference only to various degrees of approximation. The so-called heliocentric (stellar) system, with its reference point at the center of the sun (or, more accurately, at the center of mass of the solar system) and its coordinate axes directed toward three stars, may be considered an inertial frame of reference to a very high degree of accuracy. Such a frame of reference is used primarily in problems of celestial mechanics and astrogation. In practice a frame rigidly connected to the earth or, in cases that require greater accuracy (such as gyroscopy), a system with its origin at the center of the earth and its axes oriented toward the stars may serve as an inertial frame of reference for the solution of most technical problems.

In converting from one inertial frame of reference to another, Galilean transformations are valid for spatial coordinates and time in classical Newtonian mechanics, and Lorentz transformations are used in relativistic mechanics (that is, for rates of motion close to the speed of light).

S. M. TARG

References in periodicals archive ?
Observers in different moving frames will measure different relativistic masses of an object as there is no absolute frame of reference with respect to which an object's speed can be measured.
Despite the fact that young people now learn to use the relative frame of spatial orientation at school, they continue to adopt the absolute frame of reference to orient their drawings and read socio-spatial relations and movement within a drawing, just as the i r mothers do.
In the absolute frame of reference, coordinates are based on fixed or cardinal directions, as in "the boy is north of the chair" (Levinson et al.
However, choosing the one pointing to the same cardinal direction, irrespective of the participant's position, meant that the array was coded in the absolute frame of reference.
80% of the Tenejepans whose performance was consistent in at least 6 out of 8 trials coded in absolute frame of reference.
(2002: 159) referred to other studies of languages that use absolute frame of reference and pointed out that absolute responses were produced in the indoor conditions as well (Pederson et al.
As far as the 'ducks experiments' are concerned, Levinson suggests (2002: 173) that the participants understood the whole arrangement (involving the ducks) as one array, therefore they coded it using intrinsic (object in relation to another object features) not absolute frame of reference. The distinction is important, because the intrinsic frame of reference is, along with the relative one, commonly used in the languages tested.
However, given the slow-running nature of moving clocks and our inability to track time accurately, Einstein (because of his positivistic assumptions) made a fallacious inference that there is no absolute frame of reference. In light of this error, Newton's theological position of God as the objective observer of events was not at all overturned by Einstein's unjustified philosophical presupposition.
These depend on the velocity of the frame of reference with respect to which an object is being observed, not the object's velocity which can only be relative to another frame of reference, as there is no absolute frame of reference against which to measure the object's velocity.
Instead of this axiom we demand for an absolute frame of reference. As a consequence, we will arrive at transformation laws similar to Einstein's which depend on the absolute reference frame but change asymptotically to Einstein form in certain important application cases.
If an absolute frame of reference is of physical relevance, it will have an effect.
This follows from the fact that this theory is based on an absolute frame of reference. This will be further discussed below.

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