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TOPIC 6: Kinetic Molecular Model of Matter
What is Brownian motion? Brownian motion is the random motion of smoke particles in air, or tiny graphite particles placed in water.
Brownian motion is evidence that air molecules move in random directions, with random speeds (and hence kinetic energy). When these air molecules knock into the smoke particles, they cause the smoke particles to move in random motions.
Why can't we see the air molecules themselves? That's because the air molecules are invisible, even with microscopes.
As an analogy, let's compare air molecules to ghosts (both are invisible); and smoke particles to furniture (both are visible). How do we know a house is haunted, since we cannot see the ghosts? Well, we can see the tables and chairs flying all over the place (knocked by the ghosts), so we can conclude that the house is haunted.
Similarly, by looking at the random motion of the smoke particles, we know that there is something invisible (air molecules) colliding with them.
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