1. Inverse square laws.
The butter gun.

2. A nutty professor invents a butter gun
It sprays melted butter onto toast.
When the trigger is pulled, a fixed amount of butter is emitted.

3. Thickness of the butter.
The professor can spray one slice of toast from 1m distance !
The butter is too thick !
How many pieces can he spray from 2m distance ?
What is the comparative thickness ?

4. 1m 2m

5. Pieces of toast-square relationship
Distance of gun 1m 2m 3m 4m 5m
Toast spread 1 4 9 16 25

6. Comparative thickness of butter
Distance 1m 2m 3m 4m 5m
Thickness 1
1/4
1/9
1/16
1/25

7. This relationship is called the inverse square law. It applies to:
Gravitational strength with distance.
Electrostatic force with distance.
Light intensity from a point object.
Sound intensity from a point source.
Nuclear radiation from a point source.
Assuming that the light sound and radiation is not absorbed as it travels!