Physics terms: W

W

Water vapour feedbackalso water vapor feedback

A positive feedback in which warmer air holds more water vapour, a greenhouse gas, which increases the warming.

Introduced in B.2 Greenhouse effect

Wattalso watts, W

The SI unit of power: a rate of energy transfer of one joule per second.

Introduced in A.3 Work, energy and power

Wavealso waves

A disturbance that transfers energy from one place to another without a net transfer of matter.

Introduced in C.2 Wave model

Wave speedalso speed of a wave, wave velocity

The speed at which a wave transfers energy through a medium or through space, $v = f\lambda$.

Introduced in C.2 Wave model

Wave–particle dualityHL only · also wave-particle duality, duality

The behaviour of both radiation and matter as waves in some experiments (diffraction, interference) and as particles in others (photoelectric effect, Compton scattering, detection at a point).

Introduced in E.2 Quantum physics

Wavefrontalso wavefronts, wave front

A line or surface joining neighbouring points of a wave that are vibrating in phase, such as all the points on one crest. Neighbouring wavefronts are usually drawn one wavelength apart.

Introduced in C.3 Wave phenomena

Wavelengthalso wavelengths

The shortest distance between two points on a wave that are in phase, such as adjacent crests or adjacent compressions; symbol $\lambda$, in metres.

Introduced in C.2 Wave model

WeberHL only · also Wb, webers

The SI unit of magnetic flux: $1\ \text{Wb} = 1\ \text{T m}^2$, equivalent to $1\ \text{V s}$.

Introduced in D.4 Induction

Weightalso weights, gravitational force, F_g

The gravitational force on a body, $F_\mathrm{g} = mg$, measured in newtons and acting at its centre of mass.

Introduced in A.2 Forces and momentum

Weightlessnessalso weightless, apparent weightlessness

The sensation of having no weight when a body and its surroundings are in free fall together, so no support force acts on it; gravity still acts.

Introduced in D.1 Gravitational fields

White dwarfalso white dwarfs

The hot, dense, Earth-sized remnant core of a low-mass star, in which no fusion takes place; it is supported by the pressure of closely packed electrons and slowly cools.

Introduced in E.5 Fusion and stars

Wien's displacement lawalso Wien's law

The peak wavelength of a black body's spectrum is inversely proportional to its kelvin temperature: $\lambda_{\max}T = 2.9\times10^{-3}\ \text{m K}$.

Introduced in B.1 Thermal energy transfers

Workalso work done

The energy transferred when a force moves its point of application: $W = Fs\cos\theta$ for a constant force, where $\theta$ is the angle between the force and the displacement. Measured in joules.

Introduced in A.3 Work, energy and power

Work functionHL only · also work functions, Φ

The minimum energy needed to remove an electron from the surface of a metal, symbol $\Phi$; usually given in eV.

Introduced in E.2 Quantum physics

Work–energy theoremalso work-energy principle, work-energy theorem

The work done by the resultant force on a body equals the change in its kinetic energy.

Introduced in A.3 Work, energy and power

World lineHL only · also world lines, worldline

The line on a space-time diagram joining all the events in a body's history; for constant velocity it is straight, at angle $\theta$ to the $ct$ axis with $\tan\theta = v/c$.

Introduced in A.5 Galilean and special relativity