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PURPOSE

Use soda bottles and water to create both percussion and wind instruments in order to discover how changing the volume of water in a bottle affects pitch.
 

PERFORMING THE EXPERIMENT

1. If necessary, pour different amounts of water into three bottles so that the heights of water in the bottles are at 0 centimeters (cm), 3 cm, 6 cm, and 9 cm.
   
   
2. Tap the sides of the bottles gently with a spoon about three quarters of the way up the bottle where the rounded portion begins.  Are the sounds the same or different?
   
   
3. Arrange the bottles in a row from the bottle with the lowest pitch on the left to the bottle with the highest pitch on the right.  What happens to the water level as you move toward higher pitch?  Try to adjust the water levels in the bottles to obtain the pitches necessary to play "Mary Had a Little Lamb."  Were you able to do it?
   
   
4. Using present amounts of water, predict what will happen if, instead of tapping each bottle with a spoon, you blow through a straw across the top of each bottle.
   
   
5. Try it by blowing through a half straw tipped slightly downward and held just above the lip of the bottle.  You should produce the sound of a horn or whistle.
   
   
6. Arrange the bottles in a row from the bottle with the lowest pitch on the left to the bottle with the highest pitch on the right.  What happens to the water level as you move toward higher pitch?  Try to adjust the water levels in the bottles to obtain the pitches necessary to play "Mary Had a Little Lamb."  Were you able to do it?
   
   
7. Discard your half straw in the tennis ball container marked USED STRAWS.
    

QUESTION TO THINK ABOUT

1.  Why does the arrangement of the bottles change from high pitch to low pitch when you tap the bottles wit the spoon versus blowing over the top of the bottles?

EXPLANATION

When tapping the bottles, both the bottle and water are vibrating:  the larger the mass of bottle and water, the lower the rate of vibration, and the lower the pitch.  When blowing over the bottle, the air column within the bottle is vibrating:  the longer the air column, the lower the rate of vibration, and the lower the pitch.  Percussion instruments which are struck to make musical sounds are made from wood, metal, or animal hides.  Examples include wooden blocks, bells, pianos, and drums.  These instruments produce a sound when the wood, metal, or animal hides are made to vibrate.  Instruments which musicians blow into to make musical sounds are made from wooden, plastic, or metal pipes.  The pipes produce a sound when the air inside them is made to vibrate.  If the instrument is made from one very long piece of pipe, the pipe may be curled around in a circle or loop.  Instruments such as clarinets or oboes, in which the pipes are made from wood, are woodwind instruments.  Instruments such as trumpets or trombones, in which the pipes are made from metal, are called brass instruments.
 

EQUIPMENT NEEDED

4 identical glass soda bottles, metal spoon, centimeter ruler, half straws; 2-liter plastic soda bottle for water, container for extra water
 

REFERENCE

Modified from WonderScience, Fun Physical Science Activities for Children and Adults to Do Together, volume 6, number 1, January, 1992, American Chemical Society/American Institute of Physics, Washington, D.C., pages 2-3; Janice Pratt VanCleave, Physics for Every Kid, 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound, Wiley, New York, NY 1991, page 216; and Terry Cash, Steve Parker, and Barbara Taylor, 175 More Science Experiments to Amuse and Amaze Your Friends, Random House, New York, NY 1990, page 36.
 
 

Kids Involved Doing Science is at http://www.kids.union.edu

Modified 02/22/2001 by C. & P. Scaife