Extreme Science: Penny Shine

Radical Rick shows Allison Flicker how to make a Chladni Tube.

What you will need:

  • One 4X4X2 ABS-DWV (Drain waste & vent)
  • One 4” diameter ABS pipe cut at 1” in length.
    Ask at the hardware store if they have any scrap pieces of the 4” ABS pipe. Since we only need 1” in length, most stores will give you a short piece at little or no cost if you ask.
  • One 2X2X2 45 degree ABS “Y” fitting
  • One 2” ABS end cap
  • One 2' piece of 2” diameter ABS pipe cut to the following lengths
  • Large dark colored balloon (at least 12”)
  • Scissors
  • Saw
  • Sandpaper
  • Adult supervision


1) Take your 2' Piece of ABS 2” pipe and cut 1 ½” off the end of it. Insert this short piece into the 2” side of your 4X4X2 DWV as shown:

2) Attach the 2X2X2 45 degree ABS “Y” fitting as shown:

3) You will now need to cut a piece of 2” ABS pipe at approximately 6 “ in length. To determine the exact length that you will need, measure just inside the lip of the “Y” fitting down inside the lip of the end cap as shown as shown. Cut this length of pipe and press the pieces together as shown:

4) Insert the remaining length of 2” ABS pipe as shown:

5) Cut the mouthpiece off of your balloon off so that you can stretch the balloon material over the 1” long piece of 4” diameter ABS pipe as shown.

6) Press your 1”X4” ABS ring into the top 4” hole making sure that the over stretched balloon is stretched over the BOTTOM of your ring. Once it is inserted, trim, off the excess balloon material. This should give you a nice 1” deep cavity so that when you pour your salt in, it will not just spill out over the edge.

* Note: if you are having problems with the balloon staying in place, you may find that using a small amount of electrical tape to hold the balloon stretched over the end will help. Just be careful not to use too much as this will make it even harder to insert this ring into the hole.

7) Shake a small amount of salt onto the stretched out balloon. Now comes the fun part. You get to make some noise! Place your mouth into the open end of the 2” pipe and start making noises. Notice how the salt begins to vibrate and move around as the sound of your voice travels down the pipe and causes the balloon to vibrate. See how many different patterns you can make by changing the pitch of your voice.


What is going on?

The key to sound is vibration. As you make noises into your Chladni tube, you are causing the balloon to vibrate. As the balloon vibrates, the salt will get bounced around on top of the balloon. Depending on the pitch or frequency of the sound you are producing, you will begin to see patterns emerging in the salt. This is due to the fact that the varying frequencies will cause the balloon to vibrate more in some areas and less in other areas. Where the balloon vibrates more, the salt will be bounced off of those areas and tend to clollect in the ares where there is less vibration.

Try this:

Pour out the salt and pour in a SMALL amount of water instead. You want this to be a very shallow pool of water that will cover the entire balloon area. Now try making noise into the mouthpiece and see if you can get patterns to show up in the water. This may be a little more difficult but it is really cool to see the various patterns that you can obtain in the surface of the water. Have fun and remember to always clean up after yourself.

Radical Rick

Extreme Science