Does string telephone work? If yes, then how?

The Problem:

As a child we all have made our very own string telephone and talked to our friends with most of the time with very disappointing results. Sometimes we could hear the voice of the friend and most of the times we couldn't. The question is why sometimes we could hear a faint voice and at other times no voices at all? And how does it work at the fundamental level? 

Read on.

The Answer:

Let us start the answer from answering the last question first. How does the telephone actually work? If you remember the telephone would look like the following. 

Now there are two components to this entire system. Two pieces of cups, better if it is metallic. And one strong string, again better if it is metallic. 

They are connected as shown. 

So this was all about the construction. The second part is tricky and it is here why most of us never got to make these work.

If you look at the first figure the string attached to the cans has to be as tout as possible. The reason is given below.

When we speak in the can the can vibrates with the sound vibrations that we produce. These vibrations in turn are passed off to the string attached to the can. The vibrations then travel through the string and does the reverse process of vibrating the can and letting the other person hear what you say. 

For this entire process to be successful it is important that the strings be tout so that the tension along the string is evenly distributed and the sound/vibrations can travel properly without much resistance. 

So if you really want to make a string telephone make it using metal cans and keep the string tout. And ya you will need to practice a bit to find out what pitch of your voice will reach the other end as the cans may not properly vibrate thereby rendering the entire thing useless.

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