Rocket is building an ice chest for a picnic. He holds a cup of water, an ice cube and a balloon.
"These are all water or air," he says. "So why do they act so differently?"
Raven taps the ice cube. "It keeps its shape," she says. "The water takes the shape of the cup. What do you notice about the air?"
"It spreads to fill the whole balloon," Rocket says.
Nova projects three glowing boxes of dots. "Would you like a hint?" she asks. "Look at how close the dots are, and how they move."
Solids, liquids and gases are all made of particles. The difference is how strongly the particles attract each other and how they move.
| State | How close are the particles? | How do they move? |
|---|---|---|
| Solid | Very close together | Vibrate in place but cannot slide past each other |
| Liquid | Close together | Always moving and can slide past each other |
| Gas | Very far apart | Move constantly, hit each other and bounce off |
In a solid, the particles are very attracted to each other. That is why ice keeps its shape.
In a liquid, the particles still attract each other, but less. They slide, so water takes the shape of its cup.
In a gas, the particles hardly attract each other at all. They spread out to fill the whole balloon.
Every state of matter is made of particles. What changes is how strongly they attract each other.
Strong attraction holds a solid in its shape.
Weaker attraction lets a liquid flow and pour.
Very little attraction lets a gas spread out to fill any container.
| Statement | True or false? |
|---|---|
| Solid particles vibrate in place. | ? |
| Liquid particles cannot move at all. | ? |
| Gas particles are very far apart. | ? |
| Gas particles hit each other and bounce off. | ? |
Nice work picturing something you cannot see. Tomorrow you will test these ideas with your own hands.