There is this thing that is all around us, every day, everywhere, yet invisible, not noticed consciously and taken for granted. I'm talking about sound. But rather than reading, you should hear and see it, in this insanely brilliant video which makes you 'see' sound in ways like never before:
Sound is a mystery just like all the other elements of life: a bunch of atoms moving together, air pressure that goes into the ear and makes the eardrum vibrate, which creates electrical signals that get interpreted as Beethoven's 9th symphony. We use it to communicate and transport a multitude of meaning with it. Sounds can make us feel pleasant, and make us sick. But we usually don't pay much attention to sound, you could say it's invisible to us. But you can make sound visible, and the results are quite amazing!
The process of visualizing it is called 'Cymatics'.
Here is a great TED talk about it:
One of the weirdest ways to visualize sound is when you put a mix of cornstarch and water (a so-called 'non-newtonian fluid') into a loudspeaker and play a certain frequency. The pulp will start moving and looks like dancing aliens. Check it out:
You wouldn't believe it if you didn't see it with your own eyes: sound can make water flow in a spiral. By making water flow through a hose which is attached to a speaker that plays a 24Hz frequency, the water starts flowing in a spiral. Changing the frequency to 23Hz or 25Hz makes a weird forward or backward flowing effect. This is because the video camera recorded with a framerate of 24 images per second. If you see it with your own eyes, it wouldn't look that way, but the water still flows in a spiral!
Visualizing sound with fire is possible with a Ruben's tube. It's basically a tube with many holes in it, through which gas gets pumped through which escapes through the holes. If you light the gas on fire, and put a speaker next to the opening of the tube, you can see the flames 'dancing' to the music. Some engineers put this thing on a new level:
There are also unconventional and freaky ways to create sound, f.ex. with a tesla coil. Have a look at this guy, who coupled a tesla coil with his piano:
This is how it works, according to this kickstarter campaign for a DIY singing tesla coil: "Tesla coils make music by heating up air and creating pressure waves that you can hear as sound. There’s no membrane pushing air back and forth, like in a speaker or conventional instrument. The electricity itself is what you’re hearing!"
Or the band ArcAttack, which uses the sound of the electric lightenings to play music:
One more thing you can do with soundwaves is to make objects levitate: