Sound is fun to teach, and there are a ba-jillion and one demonstrations and experiments out there that showcase frequency and pitch, but not that many which address the amplitude of a sound wave.
High Amplitude Hanger
Let's change something besides the frequency!
Sound is fun to teach, and there are a ba-jillion and one demonstrations and experiments out there that showcase frequency and pitch, but not that many which address the amplitude of a sound wave. This one will absolutely blow your students away, and it is SO EASY to set up!! Don't worry, the sound produced is not deafening or disturbing - kids LOVE it and will do it for as long as you let them.
Read past the graphic for Explanations and Extensions, and thanks for trying it out!
What's Going On?
Of course all sound comes from a vibrating source, in this case, the hanger as it bumps against the desk, chair, or what have you. The metal vibrates, and that vibration is carried along the string, into your fingers, and into one of nature's great amplifiers - your skull. We don't change the frequency or pitch a lick in this experiment - but we do change the amplitude of the waves that strike your ear drums!
Have kids bump the hanger against the desk or chair WITHOUT putting their fingers in their ears. They'll feel the vibration in their fingers. They'll hear the tinny, small sound of the hanger clinking against the object. Then tell them to put their fingers in their ears and try again. Why is the sound so different? This is a great opportunity to discuss how sound is a media-dependent form of energy - that it needs a medium to travel through - and that some media conduct sound much better than others. In this case, the sound traveling through the air (fingers out of ears) is not conducted very well. Removing that poor conducting medium from the equation by sticking our fingers directly into our heads allows the sound to be conducted through a solid medium (our bodies). Wonderful!
Tell kids to try this at home. All they need is a hanger and string. Will the experiment work with a wooden hanger? How about a plastic hanger?
© Hema and Eric Bulmer. All rights reserved.