Density of air

Okay kiddo, you know how things can be heavy or light, right? Well, air is a little bit like that too. But instead of being heavy or light, we use a word called "density" to describe how much stuff is in a certain amount of air.

Imagine that you have a big jar and you fill it up with air. Now imagine that you have another jar that's the same size, but you put a bunch of heavy rocks in it instead. Which jar do you think would be heavier?

That's right, the jar with the rocks in it would be heavier. That's because the rocks are more dense than the air. There's more stuff crammed into the same amount of space.

Now, let's say we take that same jar of air and we make it really, really cold. Do you think it would be more dense or less dense than before?

Well, when things get cold, they sometimes shrink up a little bit. So when air gets really cold, it becomes more dense. There's still the same amount of air in the jar, but it takes up less space because it's squished together more.

So that's basically what we mean when we talk about the density of air. It's a way of measuring how much stuff is in a certain amount of space. And things like temperature and pressure can affect how dense the air is.