Smell the bread

About this video

Someone is baking bread in the kitchen, and a few minutes later you can smell it in your bedroom at the other end of the flat. Nothing came down the hallway that you could see. So what reached your nose?

Scientists explain this with one idea, the particle model: all matter is made of tiny particles, far too small to see even with a magnifying glass, and the particles are always moving. When bread bakes, some of its particles escape into the air. They fly about, bump into the particles of the air and slowly spread through the whole flat, until some reach your nose.

The same idea explains the three states of matter. In a solid, the particles are packed close together in tidy rows and hold on tightly, so they can only shake on the spot, and the solid keeps its shape. In a liquid they are still close, but not in rows, and they slide past each other, so a liquid flows. In a gas they are far apart and fly about fast in every direction, so a gas spreads out to fill any container.

Heating makes particles move faster. In ice they shake harder and harder until they shake loose from their rows and the ice melts. Heat the water more and some particles fly off as a gas. Cooling does the opposite. A model is a simple picture that helps explain what we see, and this one explains so much that scientists are sure the particles are there.

Transcript

1. 0:00Bread is baking in the kitchen. Minutes later, you smell it in your bedroom. What reached your nose?
2. 0:07Everything is made of tiny particles, far too small to see, and they never stop moving.
3. 0:15In a solid they sit in rows and shake. In a liquid they slide past each other. In a gas they fly far apart.
4. 0:27Heat makes them move faster. The rows shake loose, and then the particles fly off.
5. 0:38Everything is tiny particles, never still.