Join students Sophie, Tomás, Emma, and Marcus during Fifth Period! This STEM comic strip chronicles the exciting and often hilarious adventures of a close-knit group of four friends as they learn about science, technology, engineering, and math from their kooky, inspiring, off-the-wall science teacher, Mr. Kepler. When they're not in class, these kids love to explore the vast world of STEM on their own, launching weather balloons, programming computer games, and cataloging insects, sometimes with unpredictable and highly entertaining results!
Check back on the first and third Friday of every month for a new Fifth Period strip!
Loud and Crystal Clear
Tomás—never one to back down from a challenge—has heard about the myth that you can break a crystal glass using only sound…except, it’s not really a myth! It can be done! While this does take a bit of skill, Marcus is right: you don’t have to be a good singer, just able to hold a consistent tone of voice VERY LOUDLY.
How can that be done? All materials have a resonance frequency—a natural frequency at which all things vibrate—but the resonance frequency of crystal is easily observed. Just tap the crystal and listen to the beautiful tone. When you use your voice (to sing really badly, for instance), you produce pressure waves through the air: sound waves. How far apart those sound waves are from one another determines the pitch of your voice (how high or low it is)—that’s its frequency. If the frequency of your air-pressure waves matches the resonance frequency of the crystal, the crystal will vibrate on its own, producing a hum.
But what actually breaks the glass? Say you are already making sound at the correct frequency. If you increase your volume, you are adding energy (or amplitude) to your air-pressure waves. This will cause the crystal to vibrate even harder until…SNAP! The crystal breaks…or was that Marcus’s eardrums? Learn more about the physics behind breaking crystal with sound here.
Try it yourself!
We don’t want you to try and break your parents’ good crystal, but you can still experiment with the resonance frequency of crystal by wetting your finger and drawing it gently along the rim of the glass. Hear the sound it makes? Now, what happens when you fill the glass partially with water? Do you notice a change? Does the hum get higher or lower? Why do you think that is?