Philip Draviam Field Practicum 18-SEC-568 Spring Quarter Activity May 27, 2003

Unit Title: Sound and wave activity

Instructional Goals: 1. Understand how sound is produced. 2. Be aware of the fact that sound travels in the form of sound waves. 3. Understand the concepts of frequency, amplitude and period. 4. Identify any possibly factors that account for changes in frequency.

Objectives: 1. Given a simple harmonic wave, students will understand how variations in frequency, amplitude and period affect the waveform. 2. Students should understand how changes in tension, thickness and volume affect the resonating frequency of a device.

Rationale: Sound is an important phenomenon in the world around, as serves as a valuable source of information in the lives of many people. It is important to understand the many sources of sound and what factors influence the frequency, amplitude and speed of sound. Sound possesses a wave nature and can be characterized using wave theory. It is important to understand the frequencies which we are sensitive to, and how that range relates to other frequencies which are constantly being emitted.

Content: The ideas presented in this activity are appropriate for an introduction lesson to the concept of sound and its wave nature. It provides a basic understanding of sound terms such as frequency, amplitude and wavelength. These concepts can be later studied in more complex detail, but this will provide a solid understanding of the subject including real world applications.

Learning Activities: Concepts of sound (5 minutes) Begin my asking the class: How is sound produced? Listen to various responses until the correct response, “the vibration of particles in the air produce sound”, is reached. Explain that there must be atoms in the air in order for sounds to be produced. Since outer space is a vacuum, there are no particles in the air, which prevents sound from being heard.

Now ask: How does sound travel? Do theses vibrations of particles travel in a specific pattern? See if students provide the correct response (sound travels as waves), if not proceed with the tuning fork demonstration without revealing the answer. The students should be able to identify the wave patterns generated in the water by the tuning forks. Tuning Fork Example (10 minutes) 1. Tap the tuning fork to demonstrate that the vibration of the tuning fork is what is causing the audible sound. Dampen the tuning fork so that it stops vibrating, and notice that the sound stops. (Students should conclude that the vibrations cause sound). 2. While the tuning fork is vibrating, place it in a dish of water that is sitting on the overhead projector. Watch as the vibrations of the tuning fork produce sound waves. (Students should conclude that sound vibrations travel in waves). 3. Create a layer of soot on a piece of glass using the flame from a candle. Fasten a wire to one of the tuning fork prongs. Strike the tuning fork near the glass and watch as the wire creates a wave pattern in the layer of soot. (Students should conclude that sound vibrations travel in waves). 4. Strike two different tuning forks that differ in pitch. Ask the students which one has a higher pitch and explain that another word for pitch is frequency. Frequency is represented in Hertz (Hz). Write this “pitch – frequency” relationship on the board so the students understand the two words have the same meaning.

Sound in the form of waves (5 minutes) Show slide xxxxxxx to illustrate how sound waves travel from a source. Sound is distributed as a sphere from the source and each wave has the same amount of energy, which is distributed throughout the sphere. So, as the spheres get larger (which means the wave is far from the source) the intensity at a given point isn’t as much as when the sphere is smaller and the energy is contained within a small area.

Explain that humans can detect sounds that are produced with pitches/frequencies in the range of 20 – 20,000 Hz. This means that we do not hear sounds produced at frequencies that are out of this range. However certain animals are sensitive to a different range of frequencies and some ranges can be illustrated by Show slide 286. Mention that human voices are between the frequency range of 100-500 Hz.

Oscilloscope Demonstration (5 minutes) Sounds waves cannot be visualized however can be measured using an oscilloscope. A perfect pitch can be represented by a sinusoidal wave. A function generator can be used to produce these waves. Connect function generator to an oscilloscope to demonstrate what a harmonic sound wave looks like.

Once a wave has been established, increase the amplitude and ask the students if they though the original wave or the wave with the higher amplitude will be louder. Explain to them the relationship between “loudness – amplitude”, and write this relationship on the board. Loudness can be measured using a decibel meter and is measured in units of decibels. Show slide xxxxxxx illustrating some typical sounds at different decibel levels.

Engineering example – The decibel scale is important for determining what levels of sound exposure are safe. It is widely used throughout industry and many standards are established as to what levels of noise exposure are permitted during different jobs. Now vary the frequency of the waveform, reminding the students that the higher frequency noises are those with higher pitches, and lower frequency noises have lower pitches. Cycle the oscilloscope between 20 Hz and 20,000 Hz to demonstrate what a wide range of frequencies we are sensitive to. Tell the students that they will have more time to experiment with these parameters at one of the stations.

Hands on activities (~30 minutes) Students will identify what factors affect frequency by walking around the room and spending 4 minutes at each of the stations. Each student will have a worksheet to be completed as they experiment at each of the stations.

Station A: Glasses with different heights of water in them. Students may gently strike the cup using a rod and hear the different frequencies.

Station B: Strings of different lengths with identical diameters. Students can pluck them to see how string length affects the pitch.

Station C: Strings of same length with varying thickness. Students can see how the thickness of a string affects the pitch.

Station D: Microphone connected to computer where speech pattern is displayed. Students can observe their speech pattern and notice the difference between male and female voices. They will also understand how complex a wave packet of human speech is.

Station E: Computer with Data Studio software opened where students can physically alter the amplitude and frequency of the waveform and see how the pitch/loudness varies with those adjustments.

Station F: Laser Disc setup where students listen to the produced frequencies and determine what their audible range is.

Station G: Decibel meter where students can record the loudness of their normal/whisper/loud talking voices.

Station H: Students will whirl around a hollow tube and should listen to the frequency as the tube is changing positions.

Design Worksheet (10 minutes) Have students return to their desks following their observations at each of the stations and have them solve some design problems on a worksheet. Example problem: 1. Sketch how you would setup 7 plastic bottles with water to create a scale. Be clear to show the amount of water in each bottle and indicate which side has the highest frequency and which has the lowest frequency.

Further examples (15 minutes) EM Spectrum - Show slide xxxxxxx to illustrate the electromagnetic spectrum. This is purely to provide the students with some idea of how this information is used in the real world. Explain that wavelength is also used when describing waves of any form, including sound waves. It is inversely proportional to frequency, which means that as the pitch/frequency increases, the wavelength decreases.

Speed of sound – The speed of sound is roughly 340 m/s when traveling through air, which is equivalent to 760 mph. This value changes depending on if it’s traveling through a different type of medium, such as water or a solid material.

Ask the class: Is the speed of sound faster than the speed of light? Think about thunder and lightning, which one do you sense first? The speed of light is nearly one million times faster than the speed of sound!

Doppler Effect Briefly explain the Doppler effect and how frequencies in the direction of the source sound higher than frequencies in the direction away from the source. Remind the students that they witnessed this phenomenon at station H. Another example is when an ambulance is racing towards you and then passes by. The siren sounds higher pitched as the vehicle is approaching, but lower pitched after it has passed you.

Show slide 287 to illustrate the Doppler effect. So the pitch heard by a stationary person with respect to the source depends on two things. How fast and in what direction the sound source is moving.

Ask the class – But what happens when the speed of the sound source exceeds the speed of sound? Is that possible??

Leads to sonic boom and mach speeds for airplanes.

Show slide illustrating fighter plane exceeding the sound barrier. (http://www.wilk4.com/misc/soundbreak.htm)

Show slide with speeds of different aircrafts. (http://www.ueet.nasa.gov/StudentSite/dynamicsofflight.html) This will provide a perspective as to how fast sound waves travel. Real world examples: 1. Every material has a natural frequency at which it vibrates called a resonant frequency. If energy is applied to a material at its resonant frequency, then it will vibrate. If enough energy is applied, it will cause the material to crack or destruct. Civil and structural engineers need to consider these factors when designing bridges or buildings, due to the vibrations from vehicles or earthquakes. 2. Electrical engineers are constantly attempting to create devices that operate at higher frequencies. Higher frequency devices result in faster operating speed devices. Cell phones operate at 900 MHz, newer ones in GHz range.

Materials: 2 Tuning forks of varying sizes Laser Disc Oscilloscope Function Generator Transparent dish of water Slide from http://www.ueet.nasa.gov/StudentSite/dynamicsofflight.html Slide from http://www.wilk4.com/misc/soundbreak.htm Teaching transparency 286 Teaching transparency 287 Decibel meter Worksheet Hollow plastic tube for station H Slide illustrating electromagnetic spectrum Slide illustrating how sound travels from a point source Slide illustrating the various decibel levels