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  2. Mass–energy equivalence - Wikipedia

    en.wikipedia.org/wiki/Mass–energy_equivalence

    Here, Einstein used V to represent the speed of light in vacuum and L to represent the energy lost by a body in the form of radiation. [5] Consequently, the equation E = mc 2 was not originally written as a formula but as a sentence in German saying that "if a body gives off the energy L in the form of radiation, its mass diminishes by ⁠ L ...

  3. Energy–momentum relation - Wikipedia

    en.wikipedia.org/wiki/Energy–momentum_relation

    Energy–momentum relation. In physics, the energy–momentum relation, or relativistic dispersion relation, is the relativistic equation relating total energy (which is also called relativistic energy) to invariant mass (which is also called rest mass) and momentum. It is the extension of mass–energy equivalence for bodies or systems with ...

  4. Annus mirabilis papers - Wikipedia

    en.wikipedia.org/wiki/Annus_Mirabilis_papers

    The equation sets forth that the energy of a body at rest (E) equals its mass (m) times the speed of light (c) squared, or E = mc 2. If a body gives off the energy L in the form of radiation, its mass diminishes by L/c 2. The fact that the energy withdrawn from the body becomes energy of radiation evidently makes no difference, so that we are ...

  5. Speed of light - Wikipedia

    en.wikipedia.org/wiki/Speed_of_Light

    For example, for visible light, the refractive index of glass is typically around 1.5, meaning that light in glass travels at ⁠ c / 1.5 ⁠ ≈ 200 000 km/s (124 000 mi/s); the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s (56 mi/s) slower than c.

  6. Foucault's measurements of the speed of light - Wikipedia

    en.wikipedia.org/wiki/Foucault's_measurements_of...

    He used carefully calibrated tuning forks to monitor the rotation rate of the air-turbine-powered mirror R, and he would typically measure displacements of the slit image on the order of 115 mm. [7] His 1879 figure for the speed of light, 299944±51 km/s, was within about 0.05% of the modern value.

  7. Mass in special relativity - Wikipedia

    en.wikipedia.org/wiki/Mass_in_special_relativity

    The relativistic mass is the sum total quantity of energy in a body or system (divided by c2). Thus, the mass in the formula is the relativistic mass. For a particle of non-zero rest mass m moving at a speed relative to the observer, one finds. In the center of momentum frame, and the relativistic mass equals the rest mass.

  8. Einstein field equations - Wikipedia

    en.wikipedia.org/wiki/Einstein_field_equations

    v. t. e. In the general theory of relativity, the Einstein field equations (EFE; also known as Einstein's equations) relate the geometry of spacetime to the distribution of matter within it. [1] The equations were published by Albert Einstein in 1915 in the form of a tensor equation [2] which related the local spacetime curvature (expressed by ...

  9. Natural units - Wikipedia

    en.wikipedia.org/wiki/Natural_units

    In physics, natural unit systems are measurement systems for which selected physical constants have been set to 1 through nondimensionalization of physical units.For example, the speed of light c may be set to 1, and it may then be omitted, equating mass and energy directly E = m rather than using c as a conversion factor in the typical mass–energy equivalence equation E = mc 2.