When I was a kid, we sang a song about bones and how they are connected. It started with the toe bone and worked its way up to the head bone, then back down again.
If we were to sing about the bones in the ear, it would be a short song: “The hammer bone’s connected to the anvil bone. The anvil bone’s connected to the stirrup bone.”
These three bones are the smallest in the human body. Their job is to receive vibrations from the eardrum, magnify the vibrations, and send them to the inner ear where they are converted to electrical signals and passed on to the brain.
The hammer bone is connected to the eardrum. When sound hits the eardrum, causing it to vibrate, the hammer vibrates, too. The hammer’s size and position give it a mechanical advantage over the anvil, so the vibrations are intensified. The third bone, the stirrup, is connected to a spiral-shaped tube that is filled with water.
Tell you what. Let’s build ourselves a human ear. It will be easy. All we need are a funnel, a balloon, a rubber band, three Popsicle sticks, a few nuts and bolts, a flexible straw, some water, thousands of tiny hair-like wires, and a degree in electrical engineering. If you don’t have an engineering degree, we’ll pause while you go get one.
Welcome back. Let’s begin.
Cut a circle of rubber from the balloon, stretch it tight, and use the rubber band to secure it over the down-spout of the funnel. That’s the eardrum. Test it by yelling into the funnel. You should feel the taut rubber vibrate. The outer ear is complete. We are one-third done. See how easy this is?
Cut the three Popsicle sticks into the shape of a hammer, anvil, and stirrup and connect them using the nuts and bolts. Glue the end of the hammer to the rubber eardrum. Great. We are two-thirds done.
Bend the flexible straw into a spiral, fill it with water, and seal the ends. Glue the outer end of the spiral to the stirrup.
Now for the fun part. Take the thousands of tiny hair-like wires and stick them, one at a time, through the sides of the straw so that half their length is in the water. Hook the outside ends of all those wires together and connect them to a computer. (You did get the degree in electrical engineering, right?)
Now shout, “Knock, knock!” into the funnel. The sound will vibrate the rubber eardrum, which will vibrate the hammer, which will intensify the vibrations by sending them to the anvil and the stirrup, which will cause the water in the spiral straw to vibrate, which will cause the hair-like wires to wiggle, which will send electrical signals to the computer. If you have done everything correctly, the computer should respond, “Why are you shouting?”
This project is graded on a pass/fail basis. If you read the column to the end, you passed.
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