The idea
Everything is made of particles too small to see, and their behaviour explains what we can see.
The theory has five claims:
- All matter is made of tiny particles.
- Every pure substance has its own kind of particle, different from others.
- The particles are always moving; warmer means faster.
- There is space between particles.
- Particles attract one another.
What it explains
| Observation | Explanation |
|---|---|
| A balloon shrinks outdoors in winter | Particles slow down, strike the walls less often and less hard |
| You smell cookies from another room | Particles spread out through the air |
| 50 mL water + 50 mL ethanol < 100 mL | Small particles settle into the spaces between larger ones |
| Solids hold their shape | Attraction wins over motion; particles vibrate in place |
graph LR S["Solid: fixed positions, vibrating"] -->|"add energy: melting"| L["Liquid: touching, sliding"] L -->|"add energy: evaporating"| G["Gas: far apart, fast"] G -->|"remove energy: condensing"| L L -->|"remove energy: freezing"| S
Temperature is motion
“Hot” is not a substance that flows into things. Temperature is a measure of the average kinetic energy of the particles. Heating something means making its particles move faster — nothing more mysterious than that.
Curriculum connection
C2.1
investigate properties, changes, and interactions of matter that are important for the dynamic equilibrium of ecosystems and their sustainability
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