Experiment 1 Ring the Bells You need: 4 or 5 glasses Water Spoon 1. Line up your glasses. 2. Fill the first glass with about an inch of water. 3. Fill the next one with about two inches of water. 4. Fill the next one with about three inches of water and so on. 5. Now take the spoon and tap each glass, one at a time. 6. Did you hear the different tones/notes from each glass. 7. If you have any musical talent (which I don’t), you can adjust the note by changing the amount of water in each glass. If you wish, you can create a water xylophone and play Yankee Doodle at the next family gathering! 
What you just did was control the natural frequency of each glass. By altering the amount of water, you altered the material and the weight of each glass. That changed the natural frequency of each glass and so each glass vibrated at a different frequency and created a different note. (Remember that the frequency of a sound determines the pitch of a sound.) Everything vibrates at a specific frequency and the frequency something vibrates at determines the sound it makes. Resonance Here’s the concept that pulls all that we’ve been talking about into one nice little package. Sound is energy right? And energy can move something against a force over a distance right? Resonance is energy moving something else. If one thing is vibrating, its vibrations may have enough energy to cause something else that has the same natural frequency to vibrate as well. We’ve talked about this a little in past lessons so it may sound a little familiar. Honestly, resonance happens with other forms of energy besides sound energy but it is most commonly noticed when it comes to sound energy. Check out this movie on resonance (Fast connection Slow Connection). Let’s play with this a bit and it should become a little clearer.
Experiment 2: Shake that Balloon Thing You Need: Stereo with speakers Keyboard or an instrument that can get fairly loud (optional) Balloon 1. Blow up the balloon fairly nice and big. 2. Turn on the stereo a bit loud. (If the neighbors complain, say that it’s for science.) 3. Place the tips of your fingers on the balloon. 4. As the stereo plays you should be able to feel the balloon vibrate. Can you feel if the balloon vibrates more or less with the high or low notes? Try balloons that are less inflated. Do you notice a difference with them? 5. If you have a piano keyboard or an instrument that can get fairly loud, play one note at a time. Go from the lowest note, to the highest note. Does the balloon vibrate with every note? Does it vibrate more with some notes than with others?
We did this same basic experiment when we talked about sound and vibration but now I want you to look at it a different way. The vibrations coming from the speaker created an energy that moved by longitudinal waves through the air. This energy causes anything that has the same natural frequency range to vibrate. The balloon has a fairly similar natural frequency range as the speakers so the sound coming from the speakers vibrated the balloon. This is resonance; one thing vibrating causing something else to vibrate. If you were able to do this experiment with the instrument, you may have noticed that at certain notes (usually the very high ones) the balloon did not vibrate. The natural frequency range of the balloon did not reach high enough to be vibrated by the high note of the instrument. Balloons that are more inflated tend to have a greater natural frequency range. Under inflated balloons seem not to resonat at higher frequencies.
Experiment 3 Swing Time 
You need: 12 to 18 inches of string A weight (a washer, ball anything that you can tie to the end of a string) Tape Table 1. Create a pendulum by tying something to the end of a string approximately 12 to 18 inches long. 2. Tape your pendulum to the side of a table. 3. Try to get you pendulum to swing by blowing gently on it. You’ll discover that you will have to time your blow just right to get your pendulum to keep swinging with a nice steady motion. For a movie of this go here (fast connection slow connection).
If you were able to get the pendulum swinging in a nice steady motion, you became a resonator and you resonated the pendulum. Did you notice that you had to blow with a very specific frequency? The timing of each blow had to be just right or else the pendulum wouldn’t swing steadily. The frequency you had to blow at is the same frequency that the pendulum has. (If you want you can determine the frequency of the pendulum just like we did during the vibrations lesson.) The frequency of your blows matched the natural frequency of the pendulum. Whenever you swing on a swing, rock a rocking chair, or yo a yo-yo, you have to match the natural frequency of the object to get it to work right. You may have notice something else here too. As you blew on the pendulum, you did not have to blow harder to get it to swing more. (Try it again if you didn’t notice this.) This is a really interesting part of resonance. As long as energy (the blow), is continued, the vibration (the swing) will get greater and greater. When you’re pumping a swing, you really don’t have to pump harder to swing more right? As long as you keep pumping, your swing will swing more and more. Specifically, the amplitude (the size) of the vibration will get greater and greater as long as energy is continuously put into the system at the correct frequency. Look up Tacoma Bridge on the internet if you’d like to see an amazing example of what resonance can do. The Tacoma Bridge collapsed due to the fact that the frequency of the winds strangely matched the natural frequency of the bridge. That bridge got to swinging and swaying so much that it finally collapsed! It is thanks to resonance that we can hear. Sound waves resonate our ear drums. We can hear sound between the frequencies of 20 Hz and 20,000 Hz. That means that our ear drums’ natural frequency is in the range of 20-20,000 Hz. So if something vibrates at that frequency, our ear drums vibrate, and we can hear it. By the way, the next time you dance, realize that you’re not just dancing, you’re resonating! You are moving your body to the frequencies of the music. The music is “moving” you, so in a way you’re resonating! So let’s get out there and hit the resonating floor! | 
