Diffusion

Diffusion is like spreading butter on toast. Imagine you have a piece of toast and you put some butter on it. Then you start spreading the butter around with a knife. As you spread the butter, it moves from one place to another until it covers the whole toast evenly.

Well, the same thing happens with things that are really small, like molecules. These tiny things are always moving around, bouncing and colliding with each other. When there are lots of molecules in one place, they can bump into each other and move around until they are evenly spread out. This is called diffusion.

Think about how when you open a bottle of perfume or a bag of popcorn, you can smell it from far away. This is because the molecules of the perfume or popcorn are spreading out and moving around in the air, reaching your nose. This is diffusion too!

So, in simple words, diffusion is when lots of tiny things move around until they are evenly spread out.