Change in the velocity of a body with respect to time. Since velocity is a vector quantity, involving both magnitude and direction, acceleration is also a vector. In order to produce an acceleration, a force must be applied to the body.
Branch of science traditionally defined as the study of matter, energy, and the relation between them; it was called natural philosophy until the late 19th cent. and is still known by this name at a few universities.
From Collins Dictionary of Astronomy Symbol: vr. The velocity of a star along the line of sight of an observer. It is calculated directly from the doppler shift (see Doppler effect) in the lines of the star's spectrum: if the star is receding there will be a redshift in its spectral lines and the radial velocity will be positive; an approaching star will produce a blueshift and the velocity will be negative.
Physical principle, enunciated by Werner Heisenberg in 1927, that places an absolute, theoretical limit on the combined accuracy of certain pairs of simultaneous, related measurements. The accuracy of a measurement is given by the uncertainty in the result; if the measurement is exact, the uncertainty is zero.
From The Penguin Dictionary of Mathematics Symbol: v. The rate of change of position with time when the direction of motion is specified. Velocity v is thus a vector quantity; its magnitude v is referred to as speed.
Draws together all aspects of energy, covering a wealth of areas throughout the natural, social and engineering sciences, providing easily accessible information about all aspects of energy, written by leading international authorities.
This comprehensive Encyclopedia covers the full history of astronomy from its ancient origins in Africa, South America, the Middle East and China to the latest developments in astrophysics and space-based research.
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