What is Water bottle full of air?

A water bottle full of air is like a balloon that’s been filled with invisible stuff we can’t see but can feel.

Imagine you have a water bottle, and it looks empty, no water, no juice, nothing inside. But actually, it's not completely empty. It's full of something else: air! Air is all around us, like the stuff that lets us breathe. When we fill up the bottle with water, we push out some air, but there’s still air left inside.

If you squeeze the bottle gently, you can feel the air inside moving, it gets squished just like your cheeks when you puff out your face to blow a balloon. If you pour water into the bottle and then shake it, sometimes bubbles come up, those are little pockets of air trying to escape.

If you drop a water bottle full of air into a bowl of water, you might see bubbles coming out. That’s because the air inside the bottle is trying to float up to the top, just like how your breath comes out when you blow bubbles!