Chapter 21 The Nature of Sound

Section 1: Objectives Describe how vibrations cause sound. Explain how sound is transmitted through a medium. Explain how the human ear works, and identify its parts. Identify ways to protect your hearing.

Components of Sound All sounds are created by vibrations. A vibration is the complete back-and- forth motion of an object or material. The next slide shows how a stereo speaker produces sound.

Components of Sound: Figure 1

Components of Sound Sound Waves are longitudinal waves that are caused by vibrations, which are then carried through a substance and transfers energy. The particles of the substance vibrate back and forth along the path that the sound waves travel. Sound is transmitted through the vibrations and collisions of the particles.

Components of Sound Sound waves travel in all directions away from their source. However, the air or other matter through which the wave is traveling does not travel with the sound waves. The particles of air only vibrate back and forth.

Components of Sound All sound waves require a medium (plural, media). A medium is a substance through which a wave can travel by vibrating particles in the material. Air is the most common medium of sound waves. There are no particles to vibrate in a vacuum. So, no sound can be made in a vacuum.

Components of Sound Your ears are divided into three regions: the outer, middle, and inner ear. The outer ear collects sound waves. Then, organs in the middle ear increase the size of the sound wave’s vibrations. The inner ear changes the vibrations into electrical signals that your brain interprets as sound.

Components of Sound: Figure 2

Components of Sound The parts of the ear must work together for you to hear. If any part of the ear is damaged or does not work properly, hearing loss or deafness may result. Loud sounds can cause damage the cochlea. Damage to the cochlea or any other part of the inner ear usually results in permanent hearing loss.

Ch. 21 Sec. 1 Recap 1) What is a vibration? 2) Explain how sound is transmitted through particles. 3) When sound travels through a medium, does the medium travel with the sound? Explain your answer. 4) What is the most common medium of sound? 5) Explain how there can be no sound in a vacuum.

Ch. 21 Sec. 1 Recap 6) List and describe the function of the 3 parts of the ear. 7) From Figure 2, what is the function of the pinna? 8) From Figure 2, list the 3 bones that act as levers to increase the size of vibrations. 9) From Figure 2, what is the eardrum? 10) From Figure 2, what is the oval window?

Ch. 21 Sec. 1 Recap 11) What is the function of the liquid in the cochlea? 12) What 2 things may be caused if part or parts of the ear do not work properly? 13) What can loud sounds cause damage to? 14) What does damage to the cochlea result in? 15) From Figure 1, what is the difference between a compression and rarefaction?

Section 2: Objectives Compare the speed of sound in different media. Explain how frequency and pitch are related. Describe the Doppler effect, and give examples. Explain how amplitude and loudness are related. Describe how amplitude and frequency can be “seen” on an oscilloscope.

Properties of Sound The speed of sound depends only on the medium in which the sound is traveling. How the Speed of Sound Can Change Sound travels quickly through air, but it travels even faster in liquids and even faster in solids. Temperature also affects the speed of sound. The cooler the medium is, the slower the speed of sound.

Properties of Sound How low or high a sound seems to be is the pitch of that sound. The pitch of a sound is related to the frequency of the sound wave. Frequency and Hearing The frequencies of some sounds are out of the range of human hearing. Sounds that have a frequency too high for people to hear are called ultrasonic.

Properties of Sound: Figure 1

Properties of Sound The Doppler Effect is the apparent change in the frequency of a sound caused by the motion of either the listener or the source of the sound. In other words, the sound source of the listener is moving causing the frequency to change. Changing the frequency affects the properties of the sound.

Properties of Sound: Figure 2

Properties of Sound The amplitude of a wave is the largest distance the particles in a wave vibrate from their rest positions. The larger the amplitude, the louder the sound. The most common unit to express loudness is the decibel (dB).

Properties of Sound A device called an oscilloscope can graph representations of sound waves, as shown below. Notice that the graphs look like transverse waves rather than longitudinal waves.

Properties of Sound A microphone attached to an oscilloscope changes a sound wave into an electrical signal. The electrical signal is graphed on the screen in the form of a wave. The graph shows the sound as if it were a transverse wave. So, the sound’s amplitude and frequency are easier to see.

Chapter 21 Sec. 2 Recap 1)What does the speed of sound depend on? 2)Rank the speed at which sound travels from 1-3 in solids, liquids, and gases. 3) What can also affect the speed of sound? 4) How do cooler temperatures affect the speed of sound? 5)What property of sound is pitch related to?

Chapter 21 Sec. 2 Recap 6) What are ultrasonic sounds? 7) T/F Some sounds have a frequency out of the range of human hearing. 8) From Figure 1, how do the closeness of air particles relate to high frequency? 9) From Figure 1, how do the closeness of air particles relate to low frequency? 10) From Figure 1, how do frequency and pitch relate?

Chapter 21 Sec. 2 Recap 11) For the Doppler Effect to occur, what changes when the sound source changes locations? 12) What does altering frequency change? 13) From Figure 2, what is the sound source? 14) From Figure 2, what is/are the listeners? 15) From Figure 2, which listener will hear waves at a higher frequency? 16) From Figure 2, which listener will hear waves at a lower frequency?

Chapter 21 Sec. 2 Recap 17) What is amplitude and how does it affect sound? 18) What is “loudness” expressed in? 19) What changes a sound wave into an electrical signal on an oscilloscope? 20) What is the importance of changing the sound wave into an electrical signal and then a visible transverse wave?

Section 3: Objectives Explain how echoes are made, and describe their use in locating objects. List examples of constructive and destructive interference of sound waves. Explain what resonance is.