Hearing Glasses (Physics Experiments)

Do you know that windows talk? Takh, tak, tak and tak. Well, not exactly. But surfaces, such as windows, vibrate to the beat of a person’s voice. Several years ago, it was discovered that spies monitored the vibration of windows by using high-tech equipment. Although the movement was very slight yet, it could be detected by a beam of laser light. By analyzing the reflected beam, the equipment could distinguish words that were spoken in secrecy.
Things Required:
Drinking glass
Wall
Radio
Directions:
Find a solid wall that divides two rooms. Place a radio in one room with the volume set to a very soft level. Shut the door and go into the adjoining room.
Place a drinking glass against the wall. The rim of the glass should lie flat against the wall. While holding the glass, place your ear against the base of the glass. What do you hear?
Move your listening device to other parts of the wall. Do some areas transmit louder sounds?

This Is What Happens:
The radio produced sound waves that travelled outward into the room. These waves struck the wall and produced very tiny vibrations. In the adjoining room, the vibrations could not be detected without the drinking glass. Although the wall was moving back and forth yet its movement was too small to produce a detectable sound wave.
By placing the drinking glass against the wall, the “air wave” was not needed. Instead, the movement of the wall was transferred directly to the glass. From there, the vibrations travelled directly to the ear and were interpreted as sound.

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