Symbol of Earth
point source which spreads its influence equally in all directions
without a limit to its range will obey the inverse square law.
This comes from strictly geometrical considerations. The intensity
of the influence at any given radius r is the source strength
divided by the area of the sphere. Being strictly geometric in
its origin, the inverse square law applies to diverse phenomena.
Point sources of gravitational force, electric field, light, sound
or radiation obey the inverse square law.
This law accounts for the fact that the intensity of gravitational
force, electric field, light, sound or radiation becomes weaker
as it spreads out from the source since the same becomes spread
over a larger area. The intensity is inversely proportional to
the distance from the source.
The Inverse Law states that as a force whether gravitational force,
electric field, light, sound or radiation becomes weaker (intensity
reduces) as it moves away from its source and spreads.
For example :
An object placed three feet away from a light source will receive
only one ninth (1 / 3 2 , the inverse of 3 squared) as much illumination
as an object placed one foot from the light.
As a person moves away from source the intensity keeps on decreasing
while the surface area increases.