The Physics of Waves

Activity: Moving Sounds

9-12 Science Std: Phys 4a

In this activity we will be Making a device to move sound from one point to another through mechanical transmission

We will look at how sound waves transmit energy and cause things to move

And we will put this idea into practice by:

taking sound made in one place changing it into a different type of motion

moving it to another place, and

changing it back into sound

We will be making a

Telephone

actually, a string telephone

OK, so how are we? You will need the following things:

2 plastic cups

2 small sticks

9 feet of string

1 person from each group get these from the side

OK, so how are we? You take 2 plastic cups that have holes punched in the bottom….

And you cut a piece of string about 6 feet long…

And you put one end of the string through the hole in the bottom of the one cup

OK, so how are we? Then you take one of the sticks

You tie the string to middle of the stick

And put the stick and string in the bottom of the cup

OK, so how are we? Then you do the same thing with a cup and a stick on the other end of the string

OK, so how are we? Then you take your two cups and move away from each other pulling the string tight

Don’t pull too tight or you will pull the string off of the stick

But pull tight enough that the string is stretched tight between the two cups

So now we are ready to talkHave one person from your group talk into one

cup

While another person from your group listens at the other cup

Make sure you are keeping the string tight while you are talking

So now we are ready to talkThen have the person that was listening the first

time talk into their cup

While the person that talked the first time listens in their cup

Does your voice get through the string?

Try some other experiments:

Will the sound stop if you pinch the string?

What happens if you use fishing line instead of the twine for the string?

Can you make a string telephone “3-way” call

How does this work?When you talked into your cup…

Your voice made sound waves that had energy…

That hit the bottom of the plastic cupAnimation courtesy of Dr. Dan Russell, Kettering University

How does this work?The energy from your voice made the bottom of the

cup vibrate back and forth – like your eardrum

How does this work?The bottom of the cup moving back and forth was

sent down the string to the other cup…..

How does this work?The string pulled on the bottom of the other cup…

making it vibrate back and forth

How does this work?The vibration of the bottom of the cup compresses

and rarefies the air in the cup

making sound waves in the air That you can hear

Where else is this used?Where else can sound wave energy move something?

How about a microphone?

Here’s how it works…

Where else is this used?Inside a microphone is a diaphragm that vibrates when sound hits it

Just like the bottom of your “cup telephone”

This vibration is converted into an electric signal

Key Points For This Lesson:

Waves carry energy from one place to another

Even though waves carry energy through matter, there is no net movement of the matter

Sound waves are longitudinal waves

Sound waves need a medium to go through – no medium, no sound waves