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If you have ever experienced a thunderstorm, you have learned a few important things about sound. First, sound travels more slowly than light. The lightning strike you see during a storm is followed by thunder several seconds later, depending on how far away the lightning was. Another thing you may have learned is that sound travels in physical waves through the air. A loud roll of thunder can shake the whole house with the strength of those waves!
Most of the time, you can’t see or feel sound waves, but there are ways to observe these waves in action. The size of the sound waves is different, depending on their source. A large sound wave has a low frequency, and we hear it as a low-pitched sound. A small sound wave has a high frequency, and we hear it as a high-pitched sound. Different animals are able to detect sound waves that we simply can’t hear! In this challenge, you will experiment with ways to “see” a sound wave.
How to do the Seeing Sound STEM Challenge
The Challenge: Observe the effect of sound waves on small particles.
Materials: Glass or metal bowl, plastic wrap, large rubber band, sprinkles, a speaker
Challenge Criteria: Place the plastic wrap tightly over the bowl. Use the rubber band to secure it around the bowl, if needed. Pour some sprinkles on top of the bowl. Place a speaker next to the bowl. Make sure the speaker touches the bowl. Then, turn up the music until you see those sprinkles dance!
Experiment with different kinds of music to see how it affects the movement of the sprinkles. Try putting the speaker inside the bowl (easiest if you use a cell phone) to see if that changes the patterns. You can also try different particles, such as uncooked rice or pepper, to compare the results.
How did the frequency of the sound (low or high) affect the movement of the sprinkles? Were there some frequencies that didn’t cause much movement at all? Could you see the pattern of sound waves in the sprinkles as they moved?
This can also be done with salt on top of a heavy piece of black cardstock, set on top of a speaker. Since the salt particles are finer than the sprinkles, you may see some new patterns emerge!