ELI5: Explain Like I'm 5

Rayleigh–Faber–Krahn inequality

Okay kiddo, have you ever played with blocks? Imagine you have three different blocks: a big one, a medium one, and a small one. Now, let's say these blocks are made of the same material and you want to figure out which one is the heaviest. How would you do it?

Well, one way to do it is to measure the mass of each block. But what if you didn't have a scale? Is there another way you could figure out which block is heaviest without actually weighing them?

That's where the Rayleigh-Faber-Krahn inequality comes in. This is a mathematical equation that helps us understand how the shape of an object affects its physical properties, like mass or density.

The inequality states that if you have two objects made of the same material, the one with the smaller volume will be denser, and therefore heavier. So, going back to our block example, the small block will be denser than the medium or large block, which means it will be the heaviest.

But why does this happen? Well, it has to do with how the atoms in the material are arranged. When you have a smaller object, the atoms are packed more tightly together, which makes the object more dense. And since density is how much mass is packed into a certain volume, a smaller object will be heavier than a larger one made of the same material.

So, in summary, the Rayleigh-Faber-Krahn inequality helps us understand how the size and shape of an object affect its physical properties, and it tells us that smaller objects made of the same material will be denser and therefore heavier.