Dr. Gadget's Science Machine
Create chimes similar to the one on your doorbell

By Joe Laszlo

A fun look at science working in the world around you, plus a cool gadget or experiment to test it out.

Aloha! How many of you have a doorbell at your house? Is it a buzzer or a bell? Look for it in your hallway. Does it have some pipes sticking out of it? If so, it is probably a type of doorbell that sounds like chimes. A chime is usually some metallic object that makes a pleasant sound when it is struck. The percussion section of an orchestra usually has chimes. They look like long shiny pipes suspended from a rack. The player uses a wooden mallet to strike them.

How does striking them make a sound? Remember sound is a vibration. This means something is moving back and forth. Striking a piece of metal causes it to start vibrating. Of course, it has to be suspended in the air when it is struck. You can't hold the metal tightly if you want it to vibrate. Otherwise, the energy of striking won't be transformed into the energy of vibration.

In the case of your door chime, the pipes are struck by some internal electrical gadgets called solenoids. A solenoid is a hollow, cylindrical electromagnet that has a smaller permanent magnet that fits inside of it. When the button outside of the door is pressed, the switch is closed and electricity flows to the solenoid. It is activated and repels or pushes the permanent magnet out of it. This strikes the chimes, and you hear the sound — if you are home!

Can any metal be a chime? Let's find out. Let's use a metal wire coat hanger. Be sure it isn't covered with a plastic coating. Get a piece of string about three feet long. Find the middle and tie it to the hook on the hanger. Use a slip knot. Hold the string somewhat close to the hook. Tap the hanger? Do you hear a sound? Is it pleasant or does it sound like noise?

Next, tie a knot in near the end of the string. Hold one end in each hand and with your index fingers, direct each knot into one of your ears. Lean foreword a bit so that the hanger is now suspended in front of you. Swing the hanger so that it hits the edge of a table or have someone tap it for you. What do you hear? Was it pleasant? Was it a surprise.

Hold the hanger at the hook and the middle of the long side and pull it into a diamond shape. Suppose you again listen to the sound through the ends of the string in each ear. What do you think you will hear? Will it be the same as the unbent hanger? Do it! What did it sound like? Did it sound the same as when the hanger was unbent? It didn't!

Now bend the hanger into a triangle that has sides of three different sizes. Suppose you listen to the sound through the string produced by striking each side. What do you think you will hear? Will it be the same as the diamond-shaped hanger? Do it! What did it sound like? Did it sound the same as when the hanger was diamond shaped? It didn't!

Now bend the hanger into a series of loops — as many as you can. Suppose you listen to the sound through the string produced by the loops. What do you think you will hear? Will it be the same as the triangle-shape hanger? Do it! What did it sound like? Did it sound the same as when the hanger was triangle-shaped? It didn't! Why not?

To answer this, bend the hanger into one large circle. Listen to the sound produced through the string as you tap the circle at a number of different places. Did they all sound the same? There's the answer. The circle sounds the same because you are causing the same length of wire to vibrate no matter where you strike it.

However, when the hanger is bent into a diamond and then into the triangle and the loops, you have different lengths of wire vibrating as you strike the parts of each different shape. The length of the vibrating metal causes the pitch or tone to change. Before you stop experimenting, you might try some suspending and listening to different sized forks and spoons from your kitchen. Also, slats of wood give some surprising results.

Until the next time, a hui hou!

"Dr. Gadget's Science Machine" is by Joe Laszlo, a retired science teacher and winner of a Presidential Award for Excellence in Science Teaching.