Understand the Movement of Particles in Diffusion

Diffusion is the spreading out of one substance into another until they are pretty much evenly spread. 

It is the random movement of particles of a substance from where there are a lot of them, to where there are fewer of them. 

Maybe it would help if we thought of the particles like a group of dogs. Dogs that don't like being around other dogs. So, because the dogs wouldn't want to be around lots of other dogs, they would try and get as far away from the other dogs as possible, to a place where there are fewer dogs. 

So eventually, the dogs would have spread out as far as possible, so they are mixed into the flowers. The dogs have diffused into the flowers!

The use of dogs here was just to show you what happens. But in real life, diffusion is the reason we can smell a bad smell over the other side of the room, and the reason that we can make yummy drinks like tea and squash. The particles in the bad smell, the tea bag and the squash all spread out from where there are lots of them to where there are fewer of them, until they are spread out as much as they can. 

Think you have got this idea? Let's see some more scientific examples in the questions that follow!