Brownian Motion
"Particles move around all the time." This is a statement we pretty much hear all the time, but where did it first come from? A long time ago, there was a botanist named Robert Brown, and he was looking at pollens suspended in water through his microscope. When we aren't applying force to stuff, they usually won't move, right? Your books won't suddenly move out of place, and your lunch won't fly out of the window, right? Well, Brown discovered something cool:
The pollens were all moving around randomly like teachers at a disco party - and the strange thing was no one was moving it.
So why did they move? This is more or less the first proof that scientists have that proofs the existence of such particles. Remember what we said about particles moving all the time because heat is giving it energy? (Particles stop moving at an extremely low temperature at about -273 C or 0 K, and that figure is still just a prediction known as Bose-Einstein state) Well, scientists now use that to explain the random motion of the pollens. Since particles are moving all the time in random directions, scientists (starting from Albert Einstein) predict that this is why pollens and other small particles move with no apparent force involved - they explain this with the theory that particles bump into other particles, causing small particles to move in random directions.
This is now known as the Brownian Motion.
You can actually observe these in multiple everyday scenarios, which include why smells from a kitchen spread!
