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A scale factor, (conventionally called the speed-of-light) relates distances measured in space to distances measured in time. The magnitude of this scale factor (nearly 300,000 kilometres or 190,000 miles in space being equivalent to one second in time), along with the fact that spacetime is a manifold, implies that at ordinary, non ...
In SI units, the values of c, h, e and k B are exact and the values of ε 0 and G in SI units respectively have relative uncertainties of 1.6 × 10 −10 [16] and 2.2 × 10 −5. [17] Hence, the uncertainties in the SI values of the Planck units derive almost entirely from uncertainty in the SI value of G.
G {\displaystyle G} electrical conductance. siemens (S) universal gravitational constant. newton meter squared per kilogram squared (N⋅m 2 /kg 2 ) shear modulus. pascal (Pa) or newton per square meter (N/m 2 ) g {\displaystyle \mathbf {g} } acceleration due to gravity.
The hertz is defined as one per second for periodic events. The International Committee for Weights and Measures defined the second as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" [3] [4] and then adds: "It follows that the hyperfine splitting in the ground state of the ...
The (two-way) wave equation is a hyperbolic partial differential equation describing waves, including traveling and standing waves; the latter can be considered as linear superpositions of waves traveling in opposite directions. This article mostly focuses on the scalar wave equation describing waves in scalars by scalar functions u = u (x, y ...
Dynamic pressure. In fluid dynamics, dynamic pressure (denoted by q or Q and sometimes called velocity pressure) is the quantity defined by: [1] where (in SI units): u is the flow speed in m/s. It can be thought of as the fluid's kinetic energy per unit volume . For incompressible flow, the dynamic pressure of a fluid is the difference between ...
Orders of magnitude (pressure) This is a tabulated listing of the orders of magnitude in relation to pressure expressed in pascals. psi values, prefixed with + and -, denote values relative to Earth's sea level standard atmospheric pressure (psig); otherwise, psia is assumed. Magnitude. Pressure. lbf/in 2 or dB.
Sound pressure is the difference, in a given medium, between average local pressure and the pressure in the sound wave. A square of this difference (i.e., a square of the deviation from the equilibrium pressure) is usually averaged over time and/or space, and a square root of this average provides a root mean square (RMS) value.