What is solid?

A solid is something that keeps its shape and doesn’t flow like water or squish like a cloud.

Imagine you have a block of wood, like the one your dad uses to hammer nails. That block stays the same, it doesn’t just melt into nothing, and it doesn’t stretch out into a long line when you push on it. That’s what makes it a solid. The tiny pieces inside it are all packed together tightly, kind of like marbles in a jar. They don’t move around much, so the whole thing stays strong and steady.

If you look at something like ice, which is also a solid, you can see that even though it’s cold, it still holds its shape. It doesn’t pour out of a cup or stretch when you press on it. That's because the tiny parts inside are all locked in place, just like marbles in a jar.

But if you warm up that ice, it becomes water, and now it can flow, which means it’s not a solid anymore. It’s like marbles turning into jelly, they move around more freely.