GlossariesIGCSE GlossariesIGCSE Physics GlossaryBrownian Motion

Brownian Motion - IGCSE Physics Definition

Reviewed by: Leander Oates

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What is Brownian motion?

In IGCSE Physics, Brownian motion refers to the random and erratic movement of tiny particles suspended in a fluid (liquid or gas). Brownian motion is caused by collisions with the smaller, fast-moving molecules of the fluid.

Diagram illustrating random bombardment of a smoke particle by gas molecules, with arrows showing the motion in various directions.
Light, fast-moving molecules collide with larger particles, giving them the appearance of random motion

Brownian motion provides evidence for the kinetic theory of matter. The kinetic theory explains that particles in fluids are always in constant, random motion.

Brownian motion can be observed by looking at smoke particles under a microscope.

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Leander Oates

Reviewer: Leander Oates

Expertise: Senior Physics Content Creator

Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.

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