Time appears to have a direction—the past lies behind, fixed and immutable, while the future lies ahead and is not necessarily fixed. Yet for the most part the laws of physics do not specify an arrow ...
Until Einstein's profound reinterpretation of the physical concepts associated with time and space, time was considered to be the same everywhere in the universe, with all observers measuring the same ...
Temporal measurement, or chronometry, takes two distinct period forms: the calendar, a mathematical abstraction for calculating extensive periods of time, and the clock, a physical mechanism that coun ...
Under the International System of Units (via the International Committee for Weights and Measures, or CIPM), since 1967 the second has been defined as the duration of 9192631770 periods of the radiati ...
The concepts of angle and radius were already used by ancient peoples of the 1st millennium BC. The Greek astronomer and astrologer Hipparchus (190–120 BC) created a table of chord functions giving t ...
Three dimensions Space curve in 3D. The position vector r is parameterized by a scalar t. At r = a the red line is the tangent to the curve, and the blue plane is normal to the curve.In three dimensio ...
Points, considered within the framework of Euclidean geometry, are one of the most fundamental objects. Euclid originally defined the point as "that which has no part". In two-dimensional Euclidean sp ...
A physical dipole consists of two equal and opposite point charges: in the literal sense, two poles. Its field at large distances (i.e., distances large in comparison to the separation of the poles) d ...
In astronomy, the minute is a unit of angle, the minute of right ascension. It is equal to 1?60 of an hour of right ascension and can be further divided into 60 seconds of right ascension. The Earth ...
Main article: History of the metreA decimal-based unit of length, the universal measure or standard was proposed in an essay of 1668 by the English cleric and philosopher John Wilkins. In 1670 Gabriel ...
The refractive index n of an optical medium is defined as the ratio of the speed of light in vacuum, c = 299792458 m/s, and the phase velocity vphase of light in the medium,n=\frac{c}{v_\text{phase}}. ...
The Greeks distinguished between several types of magnitude, including:Positive fractionsLine segments (ordered by length)Plane figures (ordered by area)Solids (ordered by volume)Angles (ordered by an ...
Imagine a beam of particles being shot through a target, and consider an infinitesimally thin slab of the target (Figure 1). The atoms (or particles) that might stop a beam particle are shown in red. ...
Boltzmann's constant, kB, is a bridge between macroscopic and microscopic physics. Macroscopically, the ideal gas law states that, for an ideal gas, the product of pressure p and volume V is proportio ...
Radiant intensity is used to characterize the emission of radiation by an antenna. Given an antenna's power density S_r (watts per square meter) when measured at some distance r from the antenna, radi ...
