Student Instruction Sheet 469

GOOD VIBRATIONS

Good Vibrations

Student Instruction Sheet

ChallengeDetermine the relationship between frequency, wavelength, period, and pitch. You will do this in three parts using WAVEPORT's Sound Creator.

In the first part, you will explore the tools and features of Sound Creator while qualitatively determining how frequency, wavelength, period, and pitch are related. The second part is an extension of the first. Upon completion of it, you will not only confirm your findings in the first part, but you will also be able to express the mathematical relationship between period and frequency. The third part is also an extension of the first. You will again confirm findings from the first part, and also express the mathematical relationship between wavelength and frequency.

Equipment and Materials

Safety Precautions Remember, follow the directions for using the equipment.

BackgroundMuch of the information about the world around you comes via waves, electromagnetic waves (light waves) and mechanical waves. Sound is a longitudinal mechanical wave. A mechanical wave is a traveling disturbance that carries energy from one place to another. As an object vibrates, it transfers energy to the particles of the matter that surround it, causing the particles to also vibrate.

Computer w/ Speakers Student Instruction Sheet DataStudio software Student Response Sheets 1 & 2 WAVEPORT plug-in

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These vibrations are manifested in a series of compressions (pulses of compressed air or other matter) and rarefactions (disturbances in the air or other matter where the pressure is lowered) as energy moves out from the source. When the vibrations reach the eardrum, it in turn vibrates. This vibration is registered in our brain as sound.

Longitudinal waves occur when a medium vibrates parallel to the direction in which the wave travels. A medium is the material through which the sound travels. Without a medium (i.e., in a vacuum such as space) there can be no sound. It is useful to represent sound waves in a wave diagram (Figure 1) in which the crests represent areas of compression of molecules in the medium, the troughs represent areas of rarefaction, and the baseline is the average or normal pressure of the molecules in the medium.

You can often create a tone by blowing air across the top of an empty glass bottle. When you add some water to the bottle and blow, the tone changes its pitch. What is it about sound waves that make one have a different pitch than another? Changing a pitch (how low or high a sound seems to be) and loudness involves changing some of the properties of a sound wave. By adding water to the bottle, you have done something to change the properties of the wave. To understand how those properties relate to each other and affect the sound, you must first understand what some of those properties are. As you read further about those properties refer to the wave diagram in Figure 2.

Wavelength is the distance between two consecutive similar points on a wave. The wave in Figure 2 has a wavelength of 0.782 meter.

Humans are generally capable of hearing sound through air with wavelengths between 0.017 m and 17 m.

The amplitude of the wave is the distance from the baseline to the crest or trough.

Figure 1 (a) Compression and rarefaction of air molecules. (b) Wave diagram corresponding to the disturbances pictured above it.

Figure 2 Six complete wavelengths.

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The speed of the wave is determined by the medium through which it travels. Table 1, displays such data. You may recall old Western movies where the cowboy puts his ear on the train track to find out if the train is coming. He will hear the train through the rails first because sound travels faster through metal than it does through the air because the sound does not obey the inverse square law.

A cycle is exactly one completion of a vibration.

Frequency is the number of waves that pass a given point per unit of time. The unit used to measure wave frequency is the hertz (Hz). This unit is named after Heinrich Hertz who was one of the first scientists to study certain types of waves. A frequency of 1 Hz is equal to one wave, or one cycle (including a compression and rarefaction) per second.

1 Hz = 1 wave/second

The wave in Figure 3 had a frequency of 20 Hz, or 20 cycles per second.

Period is defined as the amount of time required for a single cycle to pass through a given point. In Figure 3 the period is 0.00455 s.

Speed of Sound at 20C & 1 atmMaterial Speed (m/s)

Air 343Helium 1005Hydrogen 1300Water 1440Sea Water 1560Iron and Steel ~5000Glass ~4500Aluminum ~5100Hard Wood ~4000

Figure 3

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PredictBefore beginning the eLab, complete the prediction portion of the Student Response Sheet.

ExploreComputer Setup1. Launch the DataStudio program.

2. Select Open Activity from the Welcome to DataStudio window.

3. Navigate to the folder containing the DataStudio configuration files and choose

20 Sound Wave Properties CF.ds.

This is a DataStudio Workbook file configured to prompt the appropriate displays for each of the three activities in this lab.

Record Data Part 1: Identify the Functions (page 1 of the DataStudio Workbook file)1. Use your mouse cursor to manipulate each of the Sound Creator tools in the

DataStudio file. First, discover how to make the tone play. Then, with the tone playing, determine not only the function of the tool, but also how manipulating the properties of the wave affect the tone. Record your results as instructed on the Part 2 Student Response Sheet.

2. Upon completion of the questions for this section of the activity, click on the arrow next to the page number at the bottom of the computer screen to move to the next section.

Record Data Part 2: Period vs. Frequency (page 2 of the DataStudio Workbook file)In this part of the activity you will collect at least 6 data points to help determine how the period varies with the frequency. You will be entering the values into a data table in the Workbook. Be sure to enter the frequencies in the order of increasing value.

1. On page 2 of the DataStudio Workbook file, turn the sound on by clicking on the speaker.

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2. In the first cell of the table to the right of the Sound Creator display, enter the frequency (shown in the window at the top of Sound Creators display).

Note: If no data appears in the cell while you type, it is because the table is not active. To activate the table, click on the cell in which you intend to enter data. The tone will temporarily stop while the table is active, but it will resume when you click anywhere on the Sound Creator display.

3. After you enter the value for the frequency, press the Enter or Tab key to move to the next column and record the corresponding Period. After typing in the value be sure to press Enter to record it.

Note: Change the horizontal scale ( ) if you cannot see the value for the period in the display.

4. Increase the frequency by clicking the Decimal or Multiplier buttons

( ) to the RIGHT of the frequency window. Be sure that the range frequency between your first data point and last data point is at least 8,000 Hz.

5. Click on the table and enter the next set of data points.

6. Continue changing the frequency and entering data into the table until you have collected at least 6 sets of data points.

Analyze Part 2 (page 3 of the DataStudio Workbook file)Go to page 3, Period vs. FrequencyA Step Further, by clicking on the arrow by the number at the bottom of the screen. The data table from page 2 appears along with a graph plot of your data points.

1. Click on the Scale-to-Fit ( ) button on the graph toolbar to rescale the graph axes.

2. Observe the shape of the curve of your data and determine the type of mathematical expression that best describes it.

3. Click the Curve Fit button ( ) on the graph toolbar and choose the type of curve fit expression that best approximates the mathematical relationship between Frequency and Period. After you click on your selection, a plot of that

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selection appears on the graph, and box opens displaying the parameters of the fit. The closer the Mean Squared Error is to 0, the better the fit.

4. Answer the questions on the Student Response Sheet.

Record Data Part 3: Wavelength vs. FrequencyIn this part of the activity you will collect at least ten data points to help determine how the wavelength varies with the frequency. You will be entering the values into a data table in the Workbook. Be sure to enter the frequencies in the order of increasing value.

1. On page 4 of the DataStudio Workbook file, turn the sound on by clicking on the speaker.

2. In the first cell of the table to the right of the Sound Creator display, enter the frequency.

3. After you enter the value for the frequency, press the Tab key to move to the next column and record the corresponding wavelength.

4. Increase the frequency by clicking the Decimal or Multiplier buttons

to the RIGHT of the frequency window. Be sure that

the range frequency between your first data point and last data point is at least 8,000 Hz.

5. Click on the table and enter the next set of data points.

6. Continue changing the frequency and entering data into the table until you have collect at least 10 sets of data points.

Analyze Part 3 (page 5 of the DataStudio Workbook)Go to page 5, Wavelength vs. FrequencyA Step Further, by clicking on the arrow by the number at the bottom of the screen. The data table from page 5 appears along with a graph plot of your data points.

1. Click on the Scale-to-Fit button on the graph toolbar to rescale the graph axes and most adequately display your data.

2. Observe the shape of the curve of your data and determine the type of mathematical expression that best describes it.

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3. Click the Curve Fit button on the graph toolbar and choose the type of curve fit expression that best approximates the mathematical relationship between Frequency and Wavelength. After you click on your selection, a plot of that selection appears on the graph, and a box opens displaying the parameters of the fit. Be sure to note the scale factor.

4. Answer the questions and define the vocabulary words on the Student Response Sheet.

5. Follow your teachers instructions regarding cleaning up your work space.

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Student Response SheetDay 1

Name:__________________________________

Date:_______________________________

Good Vibrations

Vocabulary

Use available resources to find the definitions of the following terms:

compression: _________________________________________________

___________________________________________________________

crest: ______________________________________________________

___________________________________________________________

mechanical wave: ______________________________________________

___________________________________________________________

medium: _____________________________________________________

___________________________________________________________

rarefaction: __________________________________________________

___________________________________________________________

trough: ______________________________________________________

___________________________________________________________

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Predict

1. How do you think sound waves are created?

2. How do you think sound waves are transmitted?

Data

Note your observations for each of the activities.

Activity Description of Results (Note what you saw, heard and felt.)

Touch a vibrating tuning fork to the surface of a pan of water.

Tie a lightweight object to a piece of thread and dangle it near a vibrating tuning fork.

Blow into a straw that has a V shape snipped out of the opposite end.

Place a noise making object, such as an alarm clock with a clapper or a wound up toy cymbal-clapping monkey, into a bell jar and evacuate the air.

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Analyze

1. By what means is sound produced? Which of the four activities demonstrated this?

___________________________________________________________

___________________________________________________________

___________________________________________________________

2. What is required for sound to be present? Which activity demonstrated this?

___________________________________________________________

___________________________________________________________

___________________________________________________________

Synthesize

1. Why is it impossible for sound to occur in a vacuum?

___________________________________________________________

___________________________________________________________

___________________________________________________________

2. If a tree falls in the forest and there is no one around to hear it, does it make a sound?

___________________________________________________________

___________________________________________________________

___________________________________________________________

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Describe the Graphs

3. Label the regions of this representation of a sound wave, then, over the top of the diagram, sketch in an appropriate wave that represents the same sound.

4. Label the parts on the sound wave below

.

Figure 1

Figure 2

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Student Response SheetDay 2

Name:__________________________________

Date:_______________________________

Good Vibrations

Vocabulary

Use available resources to find the definitions of the following terms:

amplitude: ___________________________________________________

___________________________________________________________

cycle: ______________________________________________________

___________________________________________________________

frequency: ___________________________________________________

___________________________________________________________

hertz: ______________________________________________________

___________________________________________________________

loudness: ____________________________________________________

___________________________________________________________

period: _____________________________________________________

___________________________________________________________

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pitch: _______________________________________________________

___________________________________________________________

wavelength: __________________________________________________

___________________________________________________________

Predict

1. How do you think frequency, wavelength, and pitch of a sound waves are related?

___________________________________________________________

___________________________________________________________

___________________________________________________________

2. What do you think is the relationship between the frequency and period of a sound wave?

___________________________________________________________

___________________________________________________________

___________________________________________________________

Data

Part 1: Identify the Functions (DataStudio Workbook Page 1)

For each of the following tools found in Sound Creator, identify how using it affects (1) the appearance of the display and/or the waves properties and (2) the sound of the wave.

Speaker

(1) _____________________________________________________

(2) ____________________________________________________

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Amplitude Tool

(1) _____________________________________________________

(2) ____________________________________________________

Pitch Tool

(1) _____________________________________________________

_______________________________________________________

(2) ____________________________________________________

What wave property do the numbers with the units of time (s) indicate?

_______________________________________________________

Phase Tool

(1) _____________________________________________________

(2) ____________________________________________________

Horizontal Axis Buttons (Scale Buttons)

(1) _____________________________________________________

(2) ____________________________________________________

What wave property is shown in the window? _________________

Analyze

1. How did increasing and decreasing the amplitude affect the sound?

___________________________________________________________

___________________________________________________________

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___________________________________________________________

2. Explain how decreasing the period affects the:

a. frequency ____________________________________________b. pitch ________________________________________________

3. Explain how increasing the period affects the:

a. frequency ____________________________________________b. pitch ________________________________________________

4. Describe how you would adjust the frequency to get a higher-pitched tone and explain how this might affect the period.

___________________________________________________________

___________________________________________________________

___________________________________________________________

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Part 2: Period vs. Frequency

(See DataStudio Workbook page 3 for data on this activity section.)

1. What happened to the period as you increased the frequency?

___________________________________________________________

___________________________________________________________

___________________________________________________________

2. Hid did the pitch change as you increased the frequency?

___________________________________________________________

___________________________________________________________

___________________________________________________________

3. A Step FurtherWhat is the mathematical relationship between frequency and period?

___________________________________________________________

___________________________________________________________

___________________________________________________________

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Part 3: Wavelength vs. Frequency

(See DataStudio Workbook page 5 for data on this activity section.)

1. What happened to the wavelength as you increased the frequency?

___________________________________________________________

___________________________________________________________

___________________________________________________________

2. A Step FurtherWhat is the mathematical relationship between frequency and wavelength? What is the significance of the value of the scale factor?

___________________________________________________________

___________________________________________________________

___________________________________________________________

3. A Step FurtherA sound wave traveled through a piece of wood taken from a fallen tree with a frequency of 855 Hz and a wavelength of 47 m. Calculate the speed of sound in the wood?

___________________________________________________________

___________________________________________________________

___________________________________________________________

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