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A Tin Can Telephone.

The simplest means of communicating at a distance is by simply talking. How does your mother, father, brother, or sister let you know when it's time to eat and you are outside? Of course, they HOLLER! If it's your brother or sister yelling for you, most everybody on the block knows it's time for you to eat! Right? With the Tin Can Telephone (TCT for short) you can keep moderate, distant communication secret. You can communicate either by voice or Morse code with the TCT. Of course, for super secret conversations, you may want to use your "own" code.

While the Classic Tin Can Telephone used a waxed string, the one described here uses a wire since it seems to work better. If you want to use a string instead of a wire, try waxing the string first with a piece of an old candle.

What You Need

2--coffee cans (Other cans can be used. Why not experiment here?) 2--one inch long 6-32 machine screws 2--small washers 2--6-32 nuts

A length of the stiff picture hanger wire, anywhere from 20 feet for room to room communication or as long as 100 feet for those long distance chats or other types of wire can be used. (You can also try a waxed string.)

Making It

Keep an eye on the photos while you follow these steps.

(1) Use a 1/8" drill to make holes in the center of both coffee cans.

(2) Put small washers on the two 6-32 machine screws and then, from the outside, insert these screws in the holes in the bottoms of the cans. Use your hands, inside the cans, to screw on the nuts. Leave these nuts quite loose for now. Make sure the washers are on the outside of the can between the heads of the screws and the can.

(3) Twist the ends of the wires around the screws between the washers and cans. Pliers will come in handy here. NOW TIGHTEN THE NUTS!

Trying It Out

In order for the TCT to work well, the wire between the cans should be pulled tight. This is simply done by pulling on your TCT until you can feel a tug. The wire connecting the TCT's doesn't need to be straight. The TCT will work between two rooms even if the doors are closed! Hints: Because of distortion, it is sometimes difficult to understand the words spoken through the TCT. It helps to talk slowly and clearly into the can. There is no need to shout. In fact, it is easier to understand the other person when they are talking fairly softly. Also, make sure you hold the can by its sides and NOT its bottom.

Using the TCT with Morse code

The TCT works even better with Morse code messages than simply talking into it. Use a small metal spoon, coin, nail, key, or other small metal object and tap the bottom of the can. Table 1 gives the international Morse code chart. For a "dot," make a quick light tap and a slightly longer, harder tap for a dash.

How the TCT Works

Our ears can sense the vibration of air. This vibration is called sound. We can't hear real low-pitched sounds (below 20 vibrations per second) although we can sometimes "feel" these sounds if the vibrations are strong enough. (They "feel" like a rumbling sensation, something like a freight train going by.) We also can't hear extremely high pitched sounds (over 20,000 vibrations per second). This type of sound is referred to as "ultrasonic."

In air, sound travels at about 770 miles per hour although this speed varies with temperature and altitude. Sound travels even better and faster in bard, dense materials like metal than it does in air. In iron, sound travels over 11,000 miles per hour!

The fact that sound travels much better and faster in solids (like metal) is the basic reason the TCT works. When you talk into the can, the bottom of the can vibrates. This causes the wire to vibrate. The wire's vibrations travel down the wire and cause the bottom of the other can to vibrate. This causes the air in the can to vibrate, and our ears then pick up this "air" vibration and we hear it.

A similar thing happens when we send code. However, one reason why code works better than talking is that we make the bottom of our can vibrate directly when we tap it with a metal object. By the way, a doctor's stethoscope uses the same basic principle as the TCT!
Table 1

The International Morse Code

A .-
B -...
C -.-.
D -..
E .
F ..-.
G --.
H ....
I ..
J .---
K -.-
L .-..
M --
N -.
O ---
P .--.
Q --.-
R .-.
S ...
T -
U ..-
V ...-
W .--
X -..-
Y -.--
Z --..

1 .----
2 ..---
3 ...--
4 ....-
5 .....
6 -....
7 --...
8 ---..
9 ----.
0 -----

Period .-.-.-
End of Massage .-.-.
Start .-.
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Publication:Fun For Kidz
Geographic Code:1USA
Date:Sep 1, 2003
Words:812
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