Waves, Light, and Sound Unit 6

Waves and Sound Chapter 18

18-1 Wave Characteristics Learning Target: -Understand characteristics of a wave. Success Criteria: I can… -sketch a transverse wave and identify its characteristics. -discuss the relationship between the frequency and wavelength in a transverse wave. -find one variable when using the relationship between wavelength, frequency, and velocity.

18:1 Wave Characteristics Transverse Waves: A wave is a rhythmic disturbance that carries energy through matter or space. Waves tend to travel through a medium, which can be solid, liquid, or gas. Medium: A material through which a wave can transfer energy.

What kinds of waves do you know of? Radio and light waves do not require a medium.

What are the parts of a wave? In a transverse wave, the medium moves at right angles to the direction the wave travels. What are the parts of a wave? Let’s draw one!

Within a wave, you will find: Crest: The high point in a wave. Trough: The low point in a wave. Wavelength: The distance between a point on one wave and the identical point on the next wave. Amplitude: The distance from the crest (or trough) of a wave to the rest position of the medium. The amplitude corresponds to the amount of energy carried by the wave.

Do you know what frequency is, or what it is measured in? Wave Frequency: Do you know what frequency is, or what it is measured in? The frequency of a wave is the number of wave crests that pass one place each second. The unit for frequency is hertz (Hz). 1 Hz is the same as 1 wave per second. Where have we seen this before? How do you increase the frequency of a wave? Create more crests per second. How are wavelength and frequency related?

As the frequency increases in a wave, the wavelength decreases.

where ν = velocity (m/s) λ = wavelength (m) ƒ = frequency (Hz) Wave Velocity: When is a time that we might want to know how fast a wave is travelling? After an earthquake in the ocean, we can use the wave information to determine how fast a tsunami is travelling and could reach us. Wave velocity can be determined by multiplying the wavelength and frequency of the wave. *Equation:* ν = λ * ƒ where ν = velocity (m/s) λ = wavelength (m) ƒ = frequency (Hz)

Guided Practice: First, let’s practice rearranging the equation. A wave is generated in a wave pool at a water amusement park. The wavelength is 3.2 m. The frequency of the wave is 0.60 Hz. What is the velocity of the wave?

Solution to Guided Practice: Given: Unknown: λ = 3.2 m v = ? ƒ = 0.60 Hz Equation: ν = λ * ƒ Solution: v = 3.2 m * 0.60 Hz = 1.92 (2 s.f.) = 1.9 m/s

Try It With A Friend! A wave moving along a roe has a wavelength of 1.2 m and a frequency of 4.5 Hz. How fast is the wave traveling along the rope? Given: Unknown: λ = 1.2 m v = ? ƒ = 4.5 Hz Equation: ν = λ * ƒ Solution: v = 1.2 m * 4.5 Hz = 5.4 m/s

On Your Own: 1. Earthquakes can produce 3 types of waves. One of these is a transverse wave called an S wave. A typical S wave travels at 5.0 x 103 m/s. Its wavelength is about 417 m. What is the frequency? 2. A tuning fork produces a sound wave with a wavelength of 0.20 m and a velocity of 25.6 m/s. What is the frequency of the tuning fork?

Solutions: 1. Given: Unknown: λ = 417 m ƒ = ? v = 5.0 x 103 m/s Equation: ν = λ * ƒ  ƒ = v/λ Solution: ƒ = 5000/417 = 11.99 (2 s.f.) = 12 Hz 2. λ = 0.20 m ƒ = ? v = 25.6 m/s ƒ = 25.6/0.20= 128 Hz (2 s.f.) = 130 Hz

Learning Checkpoint: 1. Sketch a transverse wave and label a crest, a trough, a wavelength, and the amplitude. 2. What is the relationship between the frequency and wavelength of a water wave? 3. FM radio stations use frequencies in the megahertz (MHz) range. If your favorite radio station is at 104.1 MHz and your friend prefers a station at 101.9 MHz, whose station uses longer wavelengths? Explain your answer.

18:2 The Nature of Sound Learning Target: To understand sound waves and sound movement. Success Criteria: I can… -describe the transmission of sound through a medium. -recognize the relationships between intensity and loudness and frequency and pitch. -illustrate the Doppler effect with a practical example.

18:2 The Nature of Sound Compressional Waves: All sounds are produced by the vibrations of objects. Sound moves in a type of wave called a compressional wave. Compressional Wave: When matter vibrates in the same direction as the wave travels.

How does a compressional wave look? As the wave moves, some of it will be squeezed together. This is called a compression. As the compression expands (spreads apart), there is a less dense area that forms, called rarefaction. *Note: The matter in the medium does not move forward with the wave. Instead, only the energy is carried forward.

Does a compressional wave have all of the characteristics of a transverse wave? Yes, they also have wavelengths, frequencies, amplitudes, and velocities. A wavelength in a compressional wave is made of one compression and one rarefaction. The frequency is the number of compressions that pass a place each second.

Media and the Speed of Sound: The speed of sound waves depends on the medium through which the waves travel and the temperature of this medium. Sound can move through any media. Air is most common on Earth Moves best through solids and liquids… Why? Are there places where sound cannot be transmitted?

The temperature of the medium is also an important factor in determining the speed of sound waves. Sound moves faster at a higher temperature through a medium, than at a lower temperature through the same medium. Use your knowledge of the kinetic theory of matter to explain. The speed of sound through air at 20oC is 343 m/s (761 mph), much slower than the speed of light (approximately 3.0 x 108 m/s [671 million mph]). This is why you see things happen, before you can hear them.

Pitch is the highness or lowness of a sound. Frequency and Pitch: Pitch is the highness or lowness of a sound. The pitch you hear depends on the frequency of the sound waves. The higher the frequency, the higher the pitch.

Humans can generally hear sound frequencies from 20Hz to 20,000 Hz. Frequencies that are higher are called ultrasonic. Uses? Sonar and medical diagnosis/treatment. Frequencies that are lower are called subsonic or infrasonic. Typically produced by heavy machines and thunder. You don’t hear these, but you can feel them in your body.

Intensity and Loudness: The intensity (loudness) of sound wave depends on the amount of energy in each wave. *Intensity of a sound wave increases as its amplitude increases. Intensity is measured in decibels (dB) Loudness is the human perception of sound intensity.

Imagine that a car is running and you are driving it. The Doppler Effect: Imagine that a car is running and you are driving it. What does it sound like on the inside? If you get out of that vehicle and it drives toward you, passes, then keeps going, how would it sound to you?

The sound of the vehicle changes based on your perspective. Inside, the sound remains at the same frequency. Outside of the vehicle, it starts at a higher frequency as it drives toward you, but the frequency drops as it moves past you. This is called the Doppler Effect. The Doppler Effect is the change in frequency due to a moving wave source. In what ways do humans utilize the Doppler effect?

Learning Checkpoint: What type of waves are sound waves and how do they transfer energy? How does the temperature of the medium affect the speed of a sound wave? During a Star Wars battle scene in space, you here a Tie Fighter whiz by you. Why is this inaccurate? While on your way to school, you turned up the volume on the car radio. Which of the following quantities change as a result: velocity of sound, intensity, pitch, amplitude, frequency, wavelength, loudness? A bat in a dark cave sends out a high frequency sound wave and detects an increase in frequency after the sound wave reflects off of the prey. Describe the possible motions of the bat and the prey.

18:3 Noise Pollution Learning Target: -To understand that noise can be a pollutant. Success Criteria: I can… -analyze the role of noise as one type of pollution. -suggest 3 ways noise pollution can be reduced.

18:3 Noise Pollution Noise pollution includes sounds that are loud, annoying, or harmful. Why is too much sound a bad thing? Intense compression waves in your ear can damage nerve endings. Creatures relying on sound for navigation, breeding, and feeding purposes may not be able to find their way. Materials like glass and plaster can be broken/shattered at certain frequencies/intensities.

How can we decrease noise pollution? Reduce sound wave intensity. Quieter machinery and cars. Insulate loud areas with sound barriers.

Learning Checkpoint: What is noise pollution? How can loud sounds damage your hearing? Traffic noise is a major source of noise pollution. How could automobiles be designed to reduce this noise?

18:4 Musical Sounds Learning Target: -To understand how music is synthesized. Success Criteria: I can… -distinguish music and noise. -describe why different instruments produce sounds of different quality. -explain two types of wave interference.

18:4 Musical Sounds What is Music?: Despite what others might say, there are some important differences between music and noise. TAKE THAT GRANDMA! Music is created using specific pitches and sound quality and by following a regular pattern. Noise has no set pattern and no definite pitch.

So how does a guitar work? When you pluck a string, the waves created run back and forth along the string, causing it to vibrate at its natural frequency. The guitar frame and the air inside then absorb the energy from the string. This forced vibration makes the sound of the string louder. If the sound that reaches an object is at the same frequency as the natural frequency of the object, the object will vibrate at this frequency. This vibration is called resonance. https://www.youtube.com/watch?v=hcXbyS2Cf2o

Suppose a trumpet and flute both played a C note. Musical Sounds: Suppose a trumpet and flute both played a C note. How do they compare? How are they different? You probably realized that although playing the same note, a trumpet and a flute sound very different. Sound quality describes the differences among sounds of the same pitch and loudness.

Let’s look at that guitar again… If you pluck a string and it vibrates along its entire length, it is called the fundamental frequency. At the same time, each half of the string can vibrate on its own. This is the first overtone and its frequency is twice that of the fundamental frequency. Intensity and number of overtones vary from one instrument to another, creating their own distinct quality of sound. Timbre

Musical Scales: A musical scale consists of 8 notes. Each note has its own frequency. All 8 notes span a frequency range called an octave. The note at the top of an octave has twice the frequency of the one at the bottom.

Interference: You may have noticed that many instruments play the same note in a song at the same time. This is to create a new kind of wave. Interference is the ability of two or more waves to combine and form a new wave. Constructive interference occurs when the compressions of different waves arrive at the same place at the same time, making a sound louder. Destructive interference occurs when the compression of one wave arrives with the rarefaction of another wave. They cancel each other out, decreasing the loudness. Beats occur when two instruments play the same note, but are not in tune with each other. Here the loudness increases and decreases continually.

Sometimes, you hear a sound linger or echo because of a room’s design. Acoustics: Sometimes, you hear a sound linger or echo because of a room’s design. This is caused by the sound reflecting off of different objects at different rates, causing the waves to hit you at different rates. Reverberations are produced by many reflections of sound. Some people specialize in designing buildings and structure to get a desired sound. Acoustics is the study of sound.

Learning Checkpoint: Compare and contrast music and noise. If you were to close your eyes and listen to middle C played both on a flute and on a cello, what musical property would enable you to distinguish one instrument from another? Explain the difference between constructive and destructive interference. Intense high-frequency sound can actually cause glass to shatter. What might be happening to the glass that causes it to break? Use terms from class to describe why it is difficult for humans to imitate animal noises.