﻿

# reference frame

[1920-25]

* * *

Coordinate system that allows description of time and position of points relative to a body.

The axes, or lines, emanate from a position called the origin. As a point moves, its velocity can be described in terms of changes in displacement and direction. Reference frames are chosen arbitrarily. For example, if a person is sitting in a moving train, the description of the person's motion depends on the chosen frame of reference. If the frame of reference is the train, the person is considered to be not moving relative to the train; if the frame of reference is the Earth, the person is moving relative to the Earth.

* * *

also called  frame of reference

in dynamics, system of graduated lines symbolically attached to a body that serve to describe the position of points relative to the body. The position of a point on the surface of the Earth, for example, can be described by degrees of latitude, measured north and south from the Equator, and degrees of longitude, measured east and west from the great circle passing through Greenwich, England, and the poles.

The reference frames used in dynamics are known as coordinate systems with axes (lines) emanating from a point known as the origin. The position of a point moving parallel to a plane (plane motion) can be described by two numbers: (1) either the distances of the point from two lines at right angles to one another on the plane (rectangular coordinates), or (2) the length of a line with one end fixed at the origin and the other end at the moving point and the angle that the line makes with a fixed axis ( polar coordinates). Motion in three dimensions can be described by three rectangular coordinates or by the length of a line emanating from the origin and two angles (spherical coordinates); one of these angles is equivalent to degrees of longitude and the other to degrees of latitude. In all cases a line from the origin to the point is known as the position vector for the point. As the point moves, the position vector changes in both magnitude and direction, and the velocity of the point is defined in terms of these changes.

Strictly speaking, Newton's laws of motion are valid only in a coordinate system at rest with respect to the “fixed” stars. Such a system is known as a Newtonian, or inertial reference, frame. The laws are also valid in any set of rigid axes moving with constant velocity and without rotation relative to the inertial frame; this concept is known as the principle of Newtonian or Galilean relativity. A coordinate system attached to the Earth is not an inertial reference frame because the Earth rotates and is accelerated with respect to the Sun. Although the solutions to most engineering problems can be obtained to a satisfactory degree of accuracy by assuming that an Earth-based reference frame is an inertial one, there are some applications in which the rotation of the Earth cannot be neglected; among these is the operation of a gyroscopic compass. (See centrifugal force; Coriolis force.)

To describe the position of a point that moves relative to a body that is moving relative to the Earth, it is usually convenient to use a reference frame attached to the moving body. The motion of the piston in the engine of a moving automobile, for example, is of more interest relative to the block than relative to the ground, whereas the motion of the moving parts of the engine relative to one another may be more important than their motions relative to the block.

* * *

Universalium. 2010.

### Look at other dictionaries:

• Reference frame — may refer to:*Frame of reference, in physics *Reference frame (video), frames of a compressed video that are used to define future frames …   Wikipedia

• reference frame — noun a system that uses coordinates to establish position • Syn: ↑coordinate system, ↑frame of reference, ↑reference system • Hypernyms: ↑arrangement, ↑organization, ↑organisation, ↑system …   Useful english dictionary

• Reference frame (video) — For the physics topic, see frame of reference. Reference frames are frames of a compressed video that are used to define future frames. As such, they are only used in inter frame compression techniques. In older video encoding standards, such as… …   Wikipedia

• reference-frame velocity — nešimo greitis statusas T sritis fizika atitikmenys: angl. reference frame velocity; velocity of moving space vok. Führungsgeschwindigkeit, f rus. переносная скорость, f pranc. vitesse d’entraînement, f …   Fizikos terminų žodynas

• Rotating reference frame — A rotating frame of reference is a special case of a non inertial reference frame that is rotating relative to an inertial reference frame. An everyday example of a rotating reference frame is the surface of the Earth. (This article considers… …   Wikipedia

• Accelerated reference frame — In theoretical physics, an accelerated reference frame is usually a coordinate system or frame of reference, that undergoes a constant and continual change in velocity over time as judged from an inertial frame. An object in an accelerated frame… …   Wikipedia

• Non-inertial reference frame — A non inertial reference frame is a frame of reference that is under acceleration.[1] The laws of physics in such a frame do not take on their most simple form, as required by the theory of special relativity.[2][3] To explain the motion of… …   Wikipedia

• Regional Reference Frame Sub-Commission for Europe — Infobox Union name= EUREF country= affiliation= International Association of Geodesy members= more than 30 countries full name= Regional Reference Frame Sub Commission for Europe native name= founded= 1987 current= head= dissolved date= dissolved …   Wikipedia

• Terrestrial reference frame — A terrestrial reference frame is the reference frame as one views from earth, or from the ground of another earth like body. A terrestrial reference frame effects the way we perceive almost everything from day to day because as we live on the… …   Wikipedia