Elenco Snap Circuits SOUND &reg - Manual (Page 45)

Project 59 Cup & String Communication
How it works: When you talk into the cup, the cup
bottom vibrates back and forth from your sound
waves. The vibrations travel through the string by
pulling the string back and forth, and then make
the bottom of the second cup vibrate just like the
first cup did, producing sound waves that the
listener can hear. If the string is tight, the received
sound waves will be just like the ones sent, and
the listener hears what the talker said.
Telephones work the same way, except that
electric current replaces the string. In radio, the
changing current from a microphone is used to
encode electromagnetic waves sent through the
air, then decoded in a listening receiver.
Cups
String
Pencil
Tiny hole
Knot
String threaded
through cup bottom
Taut string
Sound, radio signals, and light all travel through air like waves travel through
water. To help you understand how they are like waves, you can make a cup
& string telephone. This common trick requires some household materials (not
included with this kit): two large plastic or paper cups, some non-stretchable
thread or kite string, and a sharp pencil. Adult supervision is recommended.
Take the cups and punch a tiny hole in the center of the bottom of each with
a sharp pencil (or something similar). Take a piece of string (use between 25
and 100 feet) and thread each end through each hole. Either knot or tape the
string so it cannot go back through the hole when the string is stretched. Now
with two people, have each one take one of the cups and spread apart until
the string is tight. The key is to make the string tight, so it’s best to keep the
string in a straight line. Now if one of you talks into one of the cups while the
other listens, the second person should be able to hear what the first person
says.
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