Understand how the random motion of microscopic particles in a suspension provides evidence for the kinetic particle model of matter.
The kinetic particle model says that all matter is made of tiny particles (atoms, molecules, ions) that are always moving. The type of motion depends on the state of matter:
When you stir a cup of tea and watch the tiny pollen grains, they move in a zig‑zag, unpredictable way. This is called Brownian motion and it occurs because the pollen grains are constantly hit by fast‑moving water molecules.
🔬 Key point: The erratic movement of suspended particles shows that the surrounding molecules are in constant, random motion – exactly what the kinetic particle model predicts.
Imagine a crowded dance floor (the liquid). Each dancer (water molecule) is moving quickly and randomly. A larger dancer (pollen grain) tries to move but keeps bumping into the others. The result is a wobbly, unpredictable path – just like Brownian motion.
The average kinetic energy of particles in a gas is related to temperature:
\$\langle E_k \rangle = \frac{3}{2}kT\$
where \$k\$ is Boltzmann’s constant and \$T\$ is absolute temperature. Higher temperature → faster particles → more vigorous Brownian motion.
| State | Particle Motion | Typical Speed |
|---|---|---|
| Solid | Vibrate about fixed positions | Low |
| Liquid | Move past each other | Moderate |
| Gas | Move freely and rapidly | High |