Is the balloon empty?

About this video

Blow into a flat balloon and it becomes round and firm. Squeeze it and it pushes back. But look inside and you see nothing at all. So what is in the balloon?

Chemistry is the science of what stuff is made of and how it changes, and scientists call stuff matter. Matter always does two things. It has mass: how much stuff there is in something, which shows up as a bigger number on a kitchen scale. And it takes up space: where one piece of matter is, another can't be at the same time. Drop a rock into a full glass of water and the water spills over, because the space is already taken.

Air does both, even though you can't see it. It takes up space, which is why the balloon is round and pushes back. And it has mass. You feel it in the wind, and there is more of it than you would think: the air in a bedroom 4 metres long and 4 metres wide has a mass of about 50 kilograms, as much as a small adult.

Some things are real but are not stuff. Light, sound, heat and shadows have no mass and don't fill up a room so that nothing else fits. They are things that happen, not stuff you could put in a jar.

Transcript

1. 0:00What is inside a blown-up balloon? It looks empty, but squeeze it and it pushes back.
2. 0:08Matter is stuff, and it does two things. It has mass, so a scale shows a number. And it takes up space, so a full glass spills.
3. 0:18Air does both. It fills the balloon. The air in a bedroom has a mass of about fifty kilograms.
4. 0:28Light, sound, heat and shadows are real. But they are not stuff.
5. 0:35Has mass, takes up space. That is matter.