# Surfin' the Waves: An Introduction to Waves Lab Richard Dreiser and April Whitt, Instructors Wardell Minor, TA

We’ve talked about waves in the introduction, but an old Chinese Proverb states:

During this lab you are going to get to "DO" waves. We will be able to use a variety of materials to do labs that will help you to develop an understanding of things like: What is a transverse wave? What is a longitudinal wave? What is a standing wave? What are frequency and wavelength? And how do they relate to one another? These and many, many, more wonderfully wavy concepts are just ahead. So grab your surfboard, err…, your pencil and your journal, and get ready to Surf the Waves!

### Getting to Know You

You will work with a partner to do this lab. You will need a Slinky®. Before we start with our workout, let’s just explore our tool, the Slinky®.

### 1

Can you :
• Can you do that with your partner? Move it from your hand to theirs and back again?
• Do you know any other Slinky® tricks to show us?

### Getting Down to Basics — Part 1

Now it’s time to get down to work. You know that there are different types of waves. You also know that there has to be a source for the wave movement. Let’s take a closer look right now.

### 2

Have your partner hold one end of the Slinky® and stretch it along a smooth floor until it is about 3 m long. Practice shaking your end of the spring sideways until you are able to send a clear pulse along it’s length. (What is this? Yes, a WAVE!) Take turns with your lab partner until each of you can make it work.

Can you make a wave reflect or bounce back? Can you and your partner move both ends of the Slinky® to make the wave meet in the middle?

Describe a transverse wave:

How many waves can you make in 10 seconds? Your partner?

 PARTNER NAME NUMBER OF WIGGLES In 10 seconds TRIAL 1 TRIAL 2 TRIAL 3 AVERAGE

### 3

Have your lab partner hold one end of the Slinky® still while you push and pull the other end. What do you observe?

How many "wiggles" can you make in at the same time? Let your partner try it. Who can make more waves?

Describe a longitudinal wave:

>How many longitudinal waves can you make in 10 seconds?

 PARTNER NAME NUMBER OF WIGGLES In 10 seconds TRIAL 1 TRIAL 2 TRIAL 3 AVERAGE

### 4

This time both you and your partner are going to hold on to opposite ends of the Slinky®. Stand about 2 meters apart. Move the ends up and down until you get the Slinky® moving in one "wave", going up and then down (it will look like the Slinky® is doing push-ups!)

How many "wiggles" can you make in at the same time? Let your partner try it. Who can make more waves?

Describe a standing wave:

### 5

Stretch the Slinky® out along the floor again, about 4 meters long. One of you will hold one end of the Slinky® still while the other generates a transverse wave in the Slinky®. Count the number of wavelengths you can make in ten seconds. Count how few you can generate in ten seconds. Now, have your lab partner try it.

 PARTNER NAME NUMBER OF WAVELENGTHS

What can you tell about the amount of effort (energy) that you put into the Slinky™? About the frequency of the waves you generate? If you have trouble seeing how many wavelengths are traveling down the Slinky®, use a Polaroid ® camera to "freeze" the action. Get the Slinky® moving, then have someone take a flash picture of the moving spring. Be sure they fit the whole spring into the picture (they'll have to stand behind and above one end of the spring) and darken the room as much as possible. When the picture develops, count how many wavelengths were traveling along the spring.

### Getting Down to Basics — Part 2

Get your journals and pencils out. You’re going to further explore waves using objects to make your waves. When you are asked to respond to questions from this point on, record the information in your journal. (Make sure each of your records all the data collected!) When it’s appropriate, use well-designed data tables; the examples for the last section should help guide you.

### 6

Switch to the telephone cord, one for both you and your partner. Have your partner hold one end of the cord tightly and walk about six paces away (I said paces, not leaps!) You hold the other end of the cord and move it up and sown to make a single wavelength. Describe the wavelength. How many paces long is it? Now switch and let your partner try to make a single wavelength. Draw a picture in your journal showing a single wavelength.

### 7

One of you create a single wavelength again. This time, count how many times his/her hand moves up and down in ten seconds in order to make that single wavelength. Divide that number by 10, to find the number of moves per second.

The frequency of the wavelength is the number of vibrations per second, OR the movements per second OR the cycles per second. Cycles per second is also known as hertz (Hz).

### 8

Now create two wavelengths in your cord. Draw a picture of what it looks like in your journal. Measure and record the frequency of the two wavelengths.

Can you follow the same procedure, only this time make three wavelengths?

What can you conclude about frequency and wavelength?

### 9

We are going to listen to some delightful sound waves. The recording is from the AstroCapella CD by the Chromatics called the Doppler Song. It will give us a chance to talk about high frequency and low frequency sound waves. Don’t forget to use your journals to record notes and questions about high and low frequency sound waves.

Using the alarm clock on a string or the sound generator, we will arrange ourselves in a circle. Next we will swing the alarm clock or sound generator. While we’re swinging, you’re listening. You will be counting the number of revolutions. Think about these things, we will be talking about them:

• Do you hear the pitch changing?
• How does the sound frequency change as the sound source moved toward you?
• How does it change when the source is moving away from you?
• Have you ever heard this effect before?
• What causes the Doppler Effect?