Particle movement

This lesson covers: 

  1. Brownian motion
  2. Diffusion
  3. The effect of temperature on particle movement

Brownian Motion

Brownian motion describes the random, zigzag movement of tiny particles when suspended in a liquid or gas.

Diagram showing Brownian motion with pollen grains in water.
  • In 1827, scientist Robert Brown observed the irregular motion of pollen particles suspended in water under a microscope.
  • This type of random particle movement was later termed Brownian motion.
  • Brownian motion involves lighter particles like air molecules colliding with heavier particles like smoke, causing the heavier particles to move around randomly.

Random motion of particles causes diffusion

Diagram showing diffusion of particles from higher concentration to lower concentration.
  • Particles randomly move around and collide.
  • This causes them to spread from areas of high concentration to areas of low concentration.
  • This continues until particles are evenly dispersed throughout.

Increasing temperature, increases particle movement

Diagram showing particle movement at low and high temperatures with slow movement and low pressure at low temperature and fast movement and high pressure at high temperature.
  • At higher temperatures, particles have more kinetic energy so move quicker and collide more forcefully.
  • With faster, more energetic motion, particles require more space between each other. This causes expansion of the material.
  • There is increased particle collision with container walls, increasing the pressure.