2 plastic cups, string, knife, clay, stickers, colored paper and glue.
1. Make clay thick cake slightly larger than the bottom of the glass and put on her plastic Cup. With a sharp knife make a hole in the bottom of the Cup.
2. Do the same with the second Cup.
3. Pull one end of the long (4-6 meters) of thread through the hole in the bottom of the Cup and tie a knot.
4. The other end of the thread pull through the bottom of the second Cup and tie a knot.
The phone is ready!
5. If desired, you can decorate the "tube" phone colorful stickers or figures cut out of colored paper.
IMPORTANT! So the phone worked, the thread must be tight. When this stretched thread should not touch any objects, including your fingers when you hold the glass..
Attaching the Cup to your ear, you can hear that says your friend on the other end of the phone in my Cup, even if he's going to whisper or speak from another room.
The cups do in this phone role simultaneously in microphone and speaker, and the thread is telephone wire. And the sound of your voice goes on a stretched string in the form of longitudinal sound waves.
By the way...
The sound is well distributed not only strings, but also in other subjects. A good conductor of sound are metals. You can verify this by tapping on the heating battery: well knock will be heard in adjacent apartments (but do not abuse this experience, okay? Your fun can disturb those who live nearby).
The drawback of this phone
It is impossible to talk over long distances, because the sound vibrations propagating through the thread, gradually fades.
Have you learned a lesson?
Can you explain why the sound stops spread throughout the thread, if it concerns an object?