# Inverse square law

eddybob123
What is the inverse square law and how do you prove it?

Mentor
What is the inverse square law and how do you prove it?

That sounds interesting. What is it? Could you provide a web link or two to help us understand your question?

How do you think something like that could be "proved"? What is the formula for the area of a sphere maybe?

Rap
For forces like electric, magnetic, and gravitation, the inverse square law says that the force from a point source gets weaker the further you go from the source of the force. It falls off as 1/r^2 where r is the distance you are from the source. You prove it by measuring it. Other things obey the inverse square law too. If you have a light source, then the amount of light landing on a fixed area (like a piece of paper) facing the source will fall off as you move the area further away. It will fall off as 1/r^2. This is the geometric inverse square law. If you have a piece of paper at distance r, and you move it to 2r, you will have to make it 2 squared or four times larger in order for it to look the same size. This kind of inverse square law you can prove with geometry.

eddybob123
are you sure? because human measurements can't really prove it

Last edited by a moderator:
Rap
are u sure? cause human measurements can't really prove it

Some forces do not obey the inverse square law, so for a general force, you can't prove it.

For the geometrical inverse square law, you can prove it, by geometry.

Gold Member
are you sure? because human measurements can't really prove it

Course we can prove it empirically. We take two pith balls and give them each a net charge and then measure the Coulombic force as a function of distance. We will see that the force drops off as 1/r^2 with some proportional constant.