Brownian motion

Particles in both liquids and gases (collectively called fluids) move randomly. This is called Brownian motion. They do this because they are bombarded by the other moving particles in the fluid. Larger particles can be moved by light, fast-moving molecules.

Brownian motion is named after the botanist Robert Brown, who first observed this in 1827. He used a microscope to look at pollen grains moving randomly in water. At this point, he could not explain why this occurred.

In a cube full of small fast-moving particles, two much larger particles appear to move at random as a result of collisions with the smaller particles.Brownian motion

But in 1905, physicist Albert Einstein explained that the pollen grains were being moved by individual water molecules. This confirmed that atoms and molecules did exist, and provided evidence for particle theory.

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