Brownian Motion | Physics for GCSE/IGCSE - Year 11 PDF Download

The Concept of Brownian Motion

• The Kinetic Theory of Matter, asserting that all matter consists of minuscule particles, was stumbled upon almost inadvertently.
  • Scottish scientist Robert Brown initially observed the erratic movement of pollen grains in water through a microscope.
  • At the time, this phenomenon remained unexplained, but it was later understood to demonstrate that substances comprise particles in perpetual motion, hence the term 'kinetic.'

• Brownian motion refers to the haphazard movement of particles within a liquid or gas, induced by numerous collisions with smaller, often imperceptible particles.
  • When minute particles like pollen or smoke are dispersed in a liquid or gas, their random and irregular movement can be observed under a microscope.

• When observing Brownian Motion, only the minute particles visible under a microscope can be detected.
  • The movement of pollen or smoke particles is observable.
  • Atoms and molecules of water or air, being even smaller, remain invisible.
• These small, swift-moving atoms and molecules interact with the larger microscopic particles.
  • These collisions provide a slight impulse to the particles, causing their speed and direction to alter randomly with each collision.
• The existence of these light, rapidly moving atoms and molecules is deduced from the motion of the microscopic particles.
  • Such deductions play a crucial role in scientific inquiry.