Sci: A spoon bell.

 Use a slip knot to attach a metal spoon to the midpoint of a 60 cm string. Wrap the ends of the string around your index fingers and rest the fingers in your ears. Rock your body so the spoon taps against the side of a table. You will be surprised by what you hear.

The materials you need and the slip-not, before it is tightened.

With a bit of imagination, you may be able to relate this to a toy, often used by children, and involving two empty tins and a single piece of string (a definition which rules out a pair of stilts). When the metal spoon taps against the table, it sends a vibration up the string, through your fingers, and into your ears. Your eardrums pick up the vibrations and send them to your brain where they are translated into sound.

Sound travels in almost anything, but why is it much clearer here? Simply, the sound travelling along a solid bounces back into the solid each time it reaches the surface. The string acts like a tunnel, guiding the sound waves along and keeping them together, instead of spreading out, so nearly all of the sound gets to your ears.

If your ear is blocked in some way, sounds may not reach the ear drum, so you cannot hear them. If the small bones in your ear are jammed, the sound will not reach the auditory (hearing) nerve. And even if the sounds get that far, the nerve that carries sound to the brain may not work. These differences can be important, especially if your name happened to be Beethoven.

The deaf composer could ‘listen’ to the piano as he played it, by holding a stick between his teeth, and pushing the other end against the piano. The sound vibrations travelled along the stick, through Beethoven’s teeth, into the bones of his skull, and so to his cochlea, where he heard them faintly, enough for him to keep composing, even after he was deaf. Whatever caused his deafness, we can tell from this that Beethoven had no problems with his auditory nerves.

Note: Try holding the string holding the spoon in your teeth: the noise is nowhere near as impressive!

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