Special relativity Key Terms

mass-energy equivalence

The principle that mass can be converted into energy and vice versa, expressed by the equation E=mc^2.

rest energy

rest energy means The energy possessed by a body at rest, calculated as E=mc^2 where m is the rest mass. In Mass and energy in relativity, use this term to connect State mass-energy equivalence. to evidence, observation and model change.

rest energy

rest energy means The energy possessed by an object at rest, calculated using E = mc². In Mass and energy in relativity, use this term to connect Calculate rest energy from mass. to evidence, observation and model change.

mass‑energy equivalence

The principle that mass can be converted into energy and vice‑versa, expressed by E = mc².

Mass-energy equivalence

The principle that mass can be converted into energy and vice versa, expressed by the equation E=mc².

Nuclear binding energy

The energy required to separate a nucleus into its constituent protons and neutrons, equal to the mass defect multiplied by c².

Mass-energy equivalence

The principle that mass can be converted into energy and vice versa, expressed by the equation E=mc².

Relativistic kinetic energy

The kinetic energy of a particle moving at relativistic speeds, calculated as K=(γ−1)mc², where γ is the Lorentz factor.

Length contraction

The reduction in the measured length of an object moving relative to an observer, given by L = L₀/γ.

Lorentz factor

Lorentz factor means The dimensionless factor γ = 1/√(1−v²/c²) that quantifies relativistic effects. In Length contraction, use this term to connect Use length contraction equations. to evidence, observation and model change.

Proper length

Proper length means The length of an object measured in its rest frame, denoted L₀. In Length contraction, use this term to connect Use length contraction equations. to evidence, observation and model change.

Observed length

Observed length means The length of a moving object measured by a stationary observer, denoted L. In Length contraction, use this term to connect Use length contraction equations. to evidence, observation and model change.

Relative velocity

The speed v of the moving object relative to the observer, expressed as a fraction of the speed of light c.

Time dilation

Time dilation means The increase in the observed time interval for a moving clock, given by Δt = γΔt₀. In Length contraction, use this term to connect Use length contraction equations. to evidence, observation and model change.

Relativistic factor

Another term for the Lorentz factor γ, used to describe both length contraction and time dilation.

Speed of light

Speed of light means The constant c ≈ 3.00×10⁸ m s⁻¹, the maximum speed at which information can travel. In Length contraction, use this term to connect Use length contraction equations. to evidence, observation and model change.

Inertial frame

A reference frame in which Newton’s first law holds, used to define proper measurements.

Relativistic length formula

The equation L = L₀√(1−v²/c²) that relates proper length to observed length.