Absorption

Think of friction. You know that annoying thing that prevents you from going a thousand miles an hour by the time you get to the bottom of the really big hill.

The thing is though, can you think of friction with sound? How about friction in water waves? How about friction in light?!?!?

Well, there must be be something otherwise sound would travel on forever right?

The truth is, there is some sort of friction in all waves, it is just called absorption.

Absorption is just when some of the wave energy gets converted into something else, usually heat, just like normal friction.

EQ - What affects absorption of waves?

Know - What effects the absorption of sound.

Do - Make a muffler for a cell phone.

Instructions

You will not be surprised to know that there is more to waves than we have thus covered. The goal of today is to figure out how frequency and absorption go together.

Table of contents

1. More About Waves
2. Absorption Activity
   1. Observations
   2. Design your own muffler
3. Conclusion
4. Prep

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More About Waves

There are somethings we haven’t told you yet. But, you can probably figure them out by now.

There are a couple of things that go in to the properties of a wave (frequency, wavelength, amplitude, and speed). Think back to the activities you did with waves a couple of classes ago and answer the following: What determines the frequency of a wave? Think back to what determined how fast the yarn wiggled… What determines the amplitude of a wave? Again, think back to what made the yarn wiggle more… What determines the speed of a wave? Think back to the lab where you were measuring the speed, what made the speed faster…

Now, we were being a bit leading, by not asking about the wavelength but here it is.

The frequency AND the amplitude, are both determined by the source, the thing that is making the wave (think of your hand and the yarn). The speed is determined by the medium (the thing the wave is traveling through) of the wave (think back to what happened when you adjusted the tension in your slinky, or that string simulation.)

The key points are to think about what is the source, and what is medium.

Absorption Activity

Your goal is to muffle the sound coming out of your phone the best you possibly can, paying attention to how different materials absorb sound differently.

To do this, you are going to systematically test different materials and see what effect they have on the sound your phone is playing. Now, in your testing you may have to mess around and try different things.

The main focus of this activity is for you to write out descriptions of what you are hearing for the different materials. Sound you can hear, light you cannot. But, for your assessment you are going to talk about absorption with light, so you can take what you learn about absorption with sound, and try it with light.

Observations

Go and collect materials from the front of the room to test muffling your speaker with

Copy the following table into your lab notebook, putting any other random items you got into the etc. spots.

Fill in the table for each of the different objects

Design your own muffler

Now that you have tried messing with all the different materials, design your own muffler for your phone that will work the best and block all frequencies.

Draw up a design and explain WHY you think your design will be best. Make your design.

Once you have made and tested your design, answer the following questions: In what ways did your design work as intended? In what ways did it work as intended or not work as intended? Did different materials absorb different frequencies? Describe what frequencies each material absorbed, high vs low. Could you make a better muffler if you think of frequencies? If so, try it! If not, explain why.

Conclusion

Answer the following in your lab notebook in complete sentences. How have I behaved in class today? How could I better contributed to a positive classroom environment. Summarize what you learned today in 1 sentence. Answer the days essential question (EQ).

Prep

Have the following kit for each group

• Pie tin
• Styrofoam plate
• Plastic Cup
• Felt
• Cotton balls

Print

• Paste-in