Sound waves are created when sounds make vibrations in the air. In this activity, your voice vibrates the air inside the cup, which are then transferred to the bottom of the cup. The bottom of the cup passes the sound waves to the string and on to the other cup.
If the string is kept tight, the sound waves will travel. If the string is loose, the sound is less.
3rd class had good fun making the telephones and were very surprised at how they worked!
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