Cut a piece of tissue paper the same length as a plastic comb (make sure the comb’s teeth are close together). Fold the tissue paper in half, wrapping it around the teeth of the comb. Place it lightly between your lips and hummm… you’ll feel an odd vibrational effect on your lips as your kazoo makes a sound! You can try different papers, including waxed paper, parchment, tracing paper, and more!
Cut the neck off a small balloon (balloons made for water bombs work well) and stretch it over the opening of a film canister. Pinch the drum head and pull up before you release – POP! You can change the pitch by adjusting the stretch of the drum head.
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Bobby Pin Strummer
Straighten three bobby pins. (A bobby pin, when straightened, has two different sides – a smooth side and a rippled side.) Wrap a rubber band tightly around the base of an empty tin can. Slip a clothespin under the rubber band, jaw-end first so it clamps onto the rim. Place three clothespins around the rim of the soup can equally spread apart (about 120 degrees apart). Clamp the rippled end of a bobby pin into each clothespin, so that your contraction now looks like a can with three legs. Strum each pin, one at a time. What happens if you clamp the pins at different heights?
What’s happening? Plucking the pins is just like plucking the string of a guitar, and when you change the heights, you’re changing the pitch. When the pin is shorter, it tends to vibrate faster, thus giving you a higher pitch.
Push the end of a length of string and a length of light thread through one hole punched in the bottom of a can. Tie the ends inside the can to a paperclip so they stay put. The can should have two different strings coming out of the bottom. Place the can near your ear as you strum each strand (hold the light taut while you pluck it – you may need an extra set of hands.) Can you make the pitch go both high and then low? What other types of string (yarn, thread, clothesline, heavy string, steel cable, fishing line, etc. ) can you use?
What’s going on? When you pluck the string, it starts vibrating (moving back and forth really fast). The vibration in the string starts the bottom of the cup vibrating, which starts the air inside the cup vibrating, too! The cup helps focus those vibrations (sounds) to your ear.
Make yourself an old-fashioned telephone by punching a small hole in the bottom of two cups (foam, paper, tin soup cans… is there a difference?) and threading string into each one. Tie the end of the string inside the cup to a paper clip so the string stays put. Does the string need to be tight, or does it work when its loose? How can you go around corners?
What’s going on? When you talk into the cup, you are making the air molecules bang around (vibrate), and some of them bang into the end with the string, which also picks up the vibration. The vibration continues along that string and into the receiver cup, which focuses the sound so you can hear it. The cup channels your voice into the other person’s ear.
Variation: Cut the phones apart and tie each end to a slinky and test it out (we call these “Space Phones”, and after you try it, you’ll see why). What happens when you bang the slinky into different things (like walls, metal chairs, wood tables, or the floor)?
Blow across the mouth of an empty soda or water bottle to make a whistling sound. Add a little water and try again. Add more water and try again. Add more water. What happens if you use a glass bottle?
Place an empty glass under the sink faucet and tap the side of it with a fork and listen to the sound. Slowly fill the glass with water while you continue to tap. What happens if you use a spoon? Knife? Whisk? Wooden spoon?
Which of the experiments above (adding water to the bottle or removing water from the bottle) increases the pitch and which decreases the pitch?
Hold one end of a ruler tightly on the table, overhanging half the length off the table. Pluck the free end and listen… (lift and let go… WHAP!) What if you make the free end of the ruler shorter? Longer? Wood? Plastic? Metal? Two rulers? Stacked? Side-by-side?
Place an alarm clock (the kind that ticks) or a timer that is ringing on a table and listen. Now place your ear on the table. Fill a zipper bag of water and press it between you and the clock to hear the difference. Next, place the clock in a closed metal can (like a cookie tin or coffee can). What about a paper bag? A glass jar? A newspaper-filled shoebox?
You can illustrate the vibrating string principle using a guitar string – when you pluck the string, your ears pick up a sound. If you have extra rubber bands, wrap them around an open shoebox to make a shoebox guitar. You can also cut a hole in the lid (image left) and use wooden pencils to lift the rubber band off the surface of the shoebox.