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.
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.