This activity will give students an intuitive feel for the physics of sound – vibration! The activity is very easy and takes 20-30 minutes to work through, and all afternoon to explore.
What you’ll need:
- A full scale of tuning forks (PH0738ALT)
- A notebook to record your results
Activity 1 - Arranging tuning forks by pitch
- Take out the tuning forks, and holding the bottom try hitting them gently on different surfaces. You can try metal, wood, your kneecap, a book. After hitting it, hold the fork tongs up to your ear.
- Can you hear the different pitches? The pitch of the tuning fork is the note it produces. It can be a low note, or a high note, or in between. When you hit the tuning fork you cause it to vibrate. The shape of the tuning fork makes it vibrate very easily and that is what makes the sound you hear.
- Which surface gives the best sound? Would it surprise you to learn that you should avoid hitting the forks on hard surfaces like metal? It can change the pitch of the tuning fork. We have found that using your kneecap works the best.
- Now that you have a good method to ping the tuning fork, see if you can arrange them from lowest to highest pitch only using the sound of the fork. Try not to cheat by looking for writing on the forks.
- Now that you have them in order you can see that they’re all labeled: C, D, E, F, G, A, B, C.
Activity 2 - Making chords with tuning forks
- See if you can make some nice chords. A chord is playing multiple notes simultaneously, so grab a few, make a fist and stick the handles between your fingers so you look a little like the Wolverine. Then rap them on your knee or a piece of wood and hold it up to your ear. Here are some combinations to try:
- C, E, G
- D, F, A
- F, A, C
- E, G, A
- C, E, D, B (this one is tough – you have to use your thumb too!)
You might notice that some chords sound happy and some sound sad. The happy ones are called major chords. The sad ones are minor chords. The last chord is called a major-7 chord. It has a funky sound like you might hear in jazz.
Activity 3 - Determine the pitch of appliances
- Use your tuning forks to determine the pitch of appliances in your house. When the dishwasher or refrigerator is running, try listening to the forks one at a time. One of the tuning forks might sound very similar to the appliance. The note that fork makes is the resonant frequency of the appliance. Anything which vibrates has a pitch associated with it, even appliances!
Activity 4 - Explore resonances in other ways
- Go to a window. One by one, you can take the forks and after making them resonate, hold the base of the tuning fork to the center of the window. You will likely find that the sound is amplified slightly. As you go through the tuning forks in order, if you’re lucky and you put them in the same spot on the window (you can use a smudge or something to mark the spot), you’ll probably find one where the sound is amplified very strongly. That tells you one of the resonant frequencies of the window!
- Other items have resonances, too. Pots and pans, bottles, drinking glasses - especially wine glasses – have resonances. In fact, fine wine glasses may even resonate by holding the tuning fork over the top of the wine glass without touching it. Try it yourself! If you don’t have a wine glass you can try using a glass bottle.
- If, after trying all your tuning forks, you can’t hear a resonance, you can try adding water to the wine glass a little bit at a time and sticking with the same tuning fork (just pick the lowest one). The water will change the resonance of the glass (or bottle) until it matches your tuning fork!
See what else you can find that has a resonant frequency!