Showing posts with label sound waves. Show all posts
Showing posts with label sound waves. Show all posts

August 16 – Happy Birthday, Hans Jenny

Posted on August 16, 2015


Today we celebrate the Father of Cymatics.

Perhaps you are unfamiliar with cymatics. I read one definition of it that I liked: it is the study of “visual sound.”
Born in Switzerland on this date in 1904, Hans Jenny studied and took photos of the effects of sound vibrations on fluids, powders, and liquid paste.

He wrote, “This is not an unregulated chaos; it is a dynamic but ordered pattern.”



Can you believe the complex patterns created
by sound on water? So beautiful!
Of course, sound waves have been studied for centuries before Jenny lived. For example, Ernst Chladni studied the symmetrical forms created when plates covered with sand are set to vibrating with a violin bow – and he did it way back in the 1700s. Actually, at least a thousand years ago some tribes in Africa began “reading” the patterns of small grains on drumheads to foretell the future. Of course, the patterns didn't actually foretell the future, but it shows us that people have known about and enjoyed the patterns made by small particles on a vibrating surface for a long, long time.

Jenny's invention, the “tonoscope,” had a resonating chamber, a sort of membrane or drumhead on top of the chamber, and some way of introducing sound into the chamber. I read that Jenny was the first to suggest that this sort of device could someday help deaf people learn to speak.

  • Watch this cool video to enjoy the patterns of visual sound on sand, water, fire, electricity - it's amazing!
  • And here is a simple way to build your own tonoscope!


Also on this date:


Joe Miller's Joke Day




























Plan ahead:

Check out my Pinterest boards for:
And here are my Pinterest boards for:

November 29, 2009

Happy Birthday, Christian Doppler

On this date in 1803, Christian Doppler was born in Salzburg, Austria. The son of a stone mason, Doppler became a mathematician and physicist. He is known for his explanation of the phenomenon called the Doppler effect.


When a tr
ain is approaching you and blowing its whistle, the whistle sounds higher-pitched than it does as it passes you and starts moving away. That's because of the Doppler effect.

Most of us have the opportunity to hear the Doppler effect in action when an emergency vehicle approaches and passes us—the siren seems higher as it nears us, then slides to a lower pitch as it passes and recedes.

Listen to the Doppler effect on a car horn here.

Why does the Doppler effect occur?


As an ambulance approaches us, emitting the siren at the same steady pitch (or frequency), the the ambulance's motion puts it closer to the sound wave that is traveling away from us. In other words, the sound waves bunch up in the direction that the ambulance is moving, and stretch out behind the ambulance. The bunched-up waves hit our ears more often, so the sound is higher. The stretched-out waves hit our ears at a lower frequenc
y and sound lower.

Some animations on this site shows how it works.

And this animation actually shows an ambulance and should be easier for young children to understand.


Note that the sound being emitted doesn't change in pitch—it just SEEMS to change to you, the listener, standing still by the road. If you were IN the ambulance, the sound would be steady and unchanging. If both you and the ambulance were still, the siren would again sound like a st
eady pitch.

The Kettering University website also has (lower down on the webpage
) an animation to explain a sonic boom. A sonic boom is made when a plane travels faster than sound—the plane passes us before the sound reaches us, and all the bunched-up sound waves sound like a single thump. (Well, okay, a double thump, one for the nose and one for the tail of the plane. Usually the two thumps are so close together, most people hear them as one.)

Here is another Doppler-effect animation—and this time, YOU control the direction and speed of the movement. Try moving it slowly at first to see the waves bunch up and stretch out. Then try moving it quickly to see what happens when a plane moves faster than sound.


And here is a YouTube video about sonic booms. Did you know that y
ou can SEE as well as HEAR a plane break the sound barrier?

The Doppler Effect in Astronomy

Christian Doppler first explained the phenomenon of the Doppler effect, not for sound, but for light waves. He had been studying binary stars; as they circle each other, each star seems to approach us slightly and then recede again, rhythmically. We see the approaching and receding motions as shifts in the star's spectrum; as a star comes closer, its light is blue-shifted, and as it recedes from us, it's red-shifted.

The Doppler effect is one tool we use to find out about the structure, history, and future of the universe—including the facts that there was a Big Bang and that, billions of years from now, the Andromeda galaxy will collide with our Milky Way galaxy!