## G : Sound and Vibration Terms, Definitions, Units, Measurements ...

*g •* giga •

gram •

gravity

**Geometric Mean** is defined as the n^{th} root of the product of n numbers.

For instance the *geometric mean* of 2 and 8 is the square root of their product i.e **√**(2 × 8) = 4 and an example of the *geometric mean* of 3 numbers would be **∛**(2 × 3 × 4) = 2.884

**giga (G)** the SI prefix = 10^{9}

See other • SI Units

**Gradian (g)** also known as a *grad*. One grad or gradian equals 9/10 of a
degree or π/200 of a
radian.

See also •

angles

**gram (g)** the unit of mass in the metric system.

The kilogram (Kg) rather than the gram is considered the base unit of mass in the SI units because the gram is so small. The old French spelling gramme is sometimes used but gm is wrong.

**Gravitation** the force of attraction between any two

masses.

**Gravitational Force** the force of attraction between the earth's mass (for example) and bodies near its surface, the further apart the less gravity. The gravitational force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them.

**Gravity (g)** the unit for measuring acceleration. For example 1 g = 9.81 m/s² is the acceleration due to gravity at the surface of the Earth.

Grazing Incidence

**Ground Effect** the ground between a noise source and the measurement point can effect the total attenuation. Soft ground as opposed to concrete, rock, etc., provides additional attenuation up to 3 dB over distances of 100 metres. The attenuation figures are frequency and source height dependent.

**Group Velocity Definition IEC 801-23-21,** velocity in the direction of propagation of a characteristic feature of the envelope of a non-sinusoidal disturbance.

● Note :

*group velocity* differs from

phase velocity only in a dispersive

medium
● Note :

*group velocity* is ordinarily the velocity of propagation of the energy associated with the disturbance.

See also • velocity

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