Sound Waves

This session looks at how sound travels in waves. What makes sound? Vibrations! When an object vibrates (moves back and forth), it makes the air around it vibrate. When the air vibrates fast enough, your may hear this movement as sound. Vibrations are responsible for the sounds we hear. We can feel vibrations in our throat as you hum. Touch your throat with the tips of your fingers and hum. Can you feel your larynx vibrating?

Oscilloscope experiment: See sounds waves! Some sounds can be seen! Experiment with a oscilloscope, which measures and create images of sound waves.

Straw Kazoo Activity: (5-10 year olds) Need 5 straws per kazoo. Have kids cut 4 straws in different lengths using a ruler and measuring 1” increments. Use a ruler and a sharpie to measure 1” from the end of the 1st straw. Mark with sharpie then cut off with scissors. Discard short pieces. On the 2nd straw measure 2” from end then cut off. Then 3” on 3rd straw and 4” on 4th straw. Leave last straw uncut. Line the straws together on the table in a row from longest to shortest. Tape all around the tops to assemble the straw kazoo. Blow over the tops of the straws, it takes practice! Plug the ends of the holes with playdough to change the pitch. Older kids: discuss how “pitch” is measured by the number of wavelengths that travel through the air per second – aka Frequency. The lower the pitch the longer the wavelength. The shorter the wavelength the higher the pitch. The frequency of sound waves is measured in hertz.

3-4 year old variation: We can feel vibrations on our lips when we play straw kazoos. Pass out a straw to each child. 1) Have them bite down one end of the straw to make it flat. 2) Cut the flattened end to make a V shape. 3) Open the flattened part of the straw a little. 4) Put the V in your mouth and blow. Now lets experiment. What happens if you make your straw kazoo a little shorter? When you cut the straw you change the length of the column of air inside the straw. When this different length of air vibrates, you hear a different sound. Does the sound get higher or lower as the straw gets shorter?

Bat-Moth Game: Using Sound to find Prey. Some animals like bats can hear ultrasound – higher decibel sounds than humans. This game introduces echolocation – using sound waves to navigate. When a bat uses echolocation it uses pulses of sound that it generates from its throat/larynx (sometimes the nose), which are forced out as sound waves into the environment. The sound waves then bounce off of objects and then the “bounced” sounds are returned to the bat’s ear. The time delay in the sound’s release and return allow the bat to measure distance and depth of objects or prey. The ears of bats are specially made to receive sound, and having two ears helps them triangulate the location of objects. When echolocation signals travel the sounds arrive at different times and different speeds to each ear. To play the game, one child is the bat and they are blindfolded. A few children are moths and everyone else is a tree. When bat says “bat” the moths respond by saying “moth”. The bat using sound to catch a moth – this is called echolocation. When a bat gets close to a tree, tree says “tree”. Kids take turn being bat and moths.