Water-Bottle Membranophone

1. Leave the cap on the bottle, but peel the label off.
2. Cut the bottle in half using scissors (or a utility knife, if an adult is doing this). Make sure you cut evenly, leaving a smooth edge. Set aside the bottom half of the bottle for another use, or recycle it.
3. Take the top half of the bottle, and use your hole punch to punch a hole as far from the cut edge as you can towards the mouth of the bottle. Put the straw through the hole to test it for size. It should be a tight fit. If the hole isn’t large enough for the diameter of the straw, repunch in nearly the same spot to widen the hole a bit.
4. Cut the fingers and thumb off the glove as a unit (in one cut). The rest of the glove should now look like a wide tube. Cut the tube open to form a rectangular sheet of pliable material—this is your membrane.
5. Stretch the membrane over the opening you cut on the bottle, making sure that the hole you punched in the side doesn’t get hidden by excess material. If you are using a balloon, cut off the narrowest part to make a large enough surface to stretch over the opening you cut on the bottle.
6. Secure the membrane to the bottle with a rubber band. Wrap the rubber band around the bottle several times, making sure that the membrane is taut.
7. Twist the cap off the bottle and set it aside.
8. Roll a piece of construction paper into a tube, making it as tight and straight as possible. Put the rolled-up tube into the neck of the bottle, where the cap had been. Let go of the paper tube when it barely touches the bottom of the membrane. It should fit securely in the bottle opening. Tape it to the neck of the bottle so it stays in place.
9. Re-insert the straw into the punched hole on the side of the bottle, and you’re ready to play! (Click to enlarge the diagram below.)
   

Now that your instrument is complete, simply blow into the straw on the side of the bottle, and your Water-Bottle Membranophone should play!

To make different sounds, you can add finger holes. To do this, pinch the paper tube slightly and cut out a diamond shape. Repeat to make more finger holes.

Membranophones are instruments that make sound from the vibrations of stretched skins or membranes. Drums, tambourines, and some gongs are common examples of membranophones.

In this Snack, as you blow into the straw, you create pressure in the space between the outer wall of the construction-paper tube and the inner wall of the water bottle. That pressure forces the membrane to rise, allowing air to flow into the top of the tube and escape out the bottom.

As the air escapes, the membrane returns to its initial position. But as you continue blowing air into the instrument, you force the membrane to rapidly rise and fall, over and over again. If you place your finger over the top of the membrane, you can feel it vibrate. These vibrations produce sound.

Opening or covering the finger holes changes the pitch of the sound. That’s because opening a hole has the same effect as shortening the length of the “pipe” (the rolled-up construction paper). The shorter the pipe, the higher the pitch of the sound.

Kazoos are membranophones that modify sounds when you speak or sing into them. Instruments like these are known as singing membranes.

Of course, your eardrum is also a membrane that reacts to the vibrations of sound. Air waves get your eardrum moving, and those vibrations are passed through your middle ear to your inner ear until, ultimately, your brain perceives the vibrations as sound.