Albert Teen

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Brownian Motion

# Brownian Motion

### Brownian Motion

Kinetic theory tells us that particles with thermal and kinetic energy are in constant random motion. The particles in a fluid collide with each other causing them to change direction randomly. This is known as Brownian Motion.

If you placed some pollen grains in water and observed them, what do you think you would see?

In 1827, the botanist Robert Brown dropped a few grains of pollen into water and observed what happened. What he found was that the pollen gains were moving around in the water! This seemed odd as pollen grains aren't alive to be moving around on their own accord, so Brown started thinking about what it was that made them move. That is also what we will be exploring in this lesson.

This movement of the pollen grains came to be known as Brownian Motion.

True or False? The particles in states of matter are constantly moving.

Which type of energy is the cause of the movement of particles?

Which energy type is the movement of particles?

Which of the following best describes the movement of the particles in states of matter?

The particles in states of matter are constantly in motion. The energy for this motion is known as kinetic energy and comes from thermal energy in the particles. The movement of the particles is random. It is known as the kinetic theory.

Which state of matter has particles moving around the most?

Which of the 3 states of matter has the weakest bonds between the particles?

The particles in a gas move the most due to there being no bonds between the particles. By contrast, the particles in a solid have strong bonds which keep them fixed in position. This is why they can only vibrate around a fixed point.

Why do the particles in fluids move in a random direction?

So if you, like the botanist Robert Brown in 1827, put pollen grains into water, you will observe them moving. What do you think is causing this movement?

The particles in a fluid move in random directions as they are constantly colliding with each other and the walls of the container. This constantly changes their direction. This is known as Brownian Motion - named after Robert Brown who, back in 1827, discovered this by looking at grains of pollen in water and wondering what caused the motion.