Term 2 Week 1

A New Term Begins...


This term, we did a lot of really fun and new stuff! Finally, on to some real Science! (After a short revision of last term's topics during the first lesson...)

This week, we learnt about Kinetic Particle Theory.

(a.k.a a big phrase to say that atoms are in continuous and random motion)

At first glance, the definition seems rather insignificant. Okay, they are constantly moving in no preset direction. What was so interesting, I thought.

Only later did I find out that the interesting part was the derivation of the theory.

Atoms are the smallest things on earth. At 10^-19m long (0.1-0.5 nanometres) they could not be seen even with the most powerful of the microscopes in the days when the theory was discovered. So during the time when we didn't have scanneling tunneling microscopes (which were only invented quite late and can see atoms), how did they even know about this theory?

The answer-brownian motion and diffusion.

Brownian motion affects everything, even us. Just that the effects on us are too small to be seen. Brownian motion is the resultant effect when we are bombarded by smaller particles. When we look through a microscope at dust particles (no not clumps of dirt but the much finer grains-but still can be seen through a normal microscope in those days), they are moving continuously and randomly. Even though there is no wind or other external force acting on them. So, how do they move?

This is because air particles, invisible to us, are constantly bombarding the dust particle at high speeds, thus resulting in the dust particle to move erratically. We can be sure that it is because of the air particles' bombardment because when the temperature rises, the motion of the dust particle increases because the air particles themselves move faster when they have more heat and thus kinetic energy.


Diffusion is the spreading of a substance throughout a fluid. When a drop of food colouring is dropped inside a cup of water, it quickly spreads throughout the liquid. This is because of kinetic particle theory. The particles of the substance move quickly, continuously and randomly thus spread throughout the water quickly yet without any identifiable pattern.

Here is a video on kinetic particle theory.