The ear converts sound waves into electrical nerve impulses, similar to a microphone. The body part normally referred to as the ear is technically called the pinna. The outer ear, or ear canal, carries sound to the eardrum protected inside of the ear. The middle ear converts sound into mechanical vibrations and applies these vibrations to the cochlea. The lever system of the middle ear takes the force exerted on the eardrum by sound pressure variations, amplifies it and transmits it to the inner ear via the oval window.
Two muscles in the middle ear protect the inner ear from very intense sounds. They react to intense sound in a few milliseconds and reduce the force transmitted to the cochlea. This protective reaction can also be triggered by your own voice, so that humming during a fireworks display, for example, can reduce noise damage.
As the middle ear bones vibrate, they vibrate the cochlea, which contains fluid. This creates pressure waves in the fluid that cause the tectorial membrane to vibrate. The motion of the tectorial membrane stimulates tiny cilia on specialized cells called hair cells. These hair cells, and their attached neurons, transform the motion of the tectorial membrane into electrical signals that are sent to the brain. The tectorial membrane vibrates at different positions based on the frequency of the incoming sound.
This allows us to detect the pitch of sound. Yet another way that people make sounds is through playing musical instruments see the previous figure. Recall that the perception of frequency is called pitch. You may have noticed that the pitch range produced by an instrument tends to depend upon its size. Small instruments, such as a piccolo, typically make high-pitch sounds, while larger instruments, such as a tuba, typically make low-pitch sounds.
High-pitch means small wavelength, and the size of a musical instrument is directly related to the wavelengths of sound it produces. So a small instrument creates short-wavelength sounds, just as a large instrument creates long-wavelength sounds.
Most of us have excellent relative pitch, which means that we can tell whether one sound has a different frequency from another. We can usually distinguish one sound from another if the frequencies of the two sounds differ by as little as 1 Hz. For example, Musical notes are particular sounds that can be produced by most instruments, and are the building blocks of a song.
In Western music, musical notes have particular names, such as A-sharp, C, or E-flat. Some people can identify musical notes just by listening to them.
This rare ability is called perfect , or absolute, pitch. When a violin plays middle C, there is no mistaking it for a piano playing the same note. The reason is that each instrument produces a distinctive set of frequencies and intensities. We call our perception of these combinations of frequencies and intensities the timbre of the sound.
It is more difficult to quantify timbre than loudness or pitch. Timbre is more subjective. Evocative adjectives such as dull, brilliant, warm, cold, pure, and rich are used to describe the timbre of a sound rather than quantities with units, which makes for a difficult topic to dissect with physics.
So the consideration of timbre takes us into the realm of perceptual psychology, where higher-level processes in the brain are dominant.
This is also true for other perceptions of sound, such as music and noise. If students are struggling with a specific objective, these questions will help identify which and direct students to the relevant content. Nave, R.
Vocal sound production—HyperPhysics. As an Amazon Associate we earn from qualifying purchases. Want to cite, share, or modify this book? This book is Creative Commons Attribution License 4. Changes were made to the original material, including updates to art, structure, and other content updates. Skip to Content Go to accessibility page. Physics My highlights. Table of contents. Changes were made to the original material, including updates to art, structure, and other content updates.
Skip to Content Go to accessibility page. Physics My highlights. Table of contents. Chapter Review. Test Prep. By the end of this section, you will be able to do the following: Relate the characteristics of waves to properties of sound waves Describe the speed of sound and how it changes in various media Relate the speed of sound to frequency and wavelength of a sound wave.
Teacher Support The learning objectives in this section will help your students master the following standards: 7 Science concepts. The student knows the characteristics and behavior of waves. The student is expected to: A examine and describe oscillatory motion and wave propagation in various types of media; B investigate and analyze characteristics of waves, including velocity, frequency, amplitude, and wavelength, and calculate using the relationship between wave speed, frequency, and wavelength; C compare characteristics and behaviors of transverse waves, including electromagnetic waves and the electromagnetic spectrum, and characteristics and behaviors of longitudinal waves, including sound waves; F describe the role of wave characteristics and behaviors in medical and industrial applications.
In addition, the High School Physics Laboratory Manual addresses content in this section in the lab titled: Waves, as well as the following standards: 7 Science concepts. The student is expected to: B investigate and analyze characteristics of waves, including velocity, frequency, amplitude, and wavelength, and calculate using the relationship between wave speed, frequency, and wavelength. Teacher Support [BL] [OL] Review waves and types of waves—mechanical and non-mechanical, transverse and longitudinal, pulse and periodic.
The graph shows gauge pressure P gauge versus distance x from the source. Gauge pressure is the pressure relative to atmospheric pressure; it is positive for pressures above atmospheric pressure, and negative for pressures below it. For ordinary, everyday sounds, pressures vary only slightly from average atmospheric pressure. There is a net force on the eardrum, since the sound wave pressures differ from the atmospheric pressure found behind the eardrum.
A complicated mechanism converts the vibrations to nerve impulses, which are then interpreted by the brain. Teacher Support [BL] Review the fact that sound is a mechanical wave and requires a medium through which it is transmitted.
Teacher Support Students might be confused between rigidity and density and how they affect the speed of sound. Teacher Support [BL] Note that in the table, the speed of sound in very rigid materials such as glass, aluminum, and steel Sound travels more slowly than light does. Dominic Alves, Flickr. Teacher Support Hold a meter stick flat on a desktop, with about 80 cm sticking out over the edge of the desk. Teacher Support [AL] Ask students to predict what would happen if the speeds of sound in air varied by frequency.
Sound Click to view content. PhET Explorations: Sound. Adjust the frequency or volume and you can see and hear how the wave changes.
Click to view content. In the first tab, Listen to a Single Source, move the listener as far away from the speaker as possible, and then change the frequency of the sound wave.
You may have noticed that there is a delay between the time when you change the setting and the time when you hear the sound get lower or higher in pitch. Why is this? Is there a difference in the amount of delay depending on whether you make the frequency higher or lower?
Voice as a Sound Wave In this lab you will observe the effects of blowing and speaking into a piece of paper in order to compare and contrast different sound waves. What Are the Wavelengths of Audible Sounds? Echolocation Figure The time for the echo to return is directly proportional to the distance. If a predator is directly to the left of a bat, how will the bat know? What is a rarefaction? Simple harmonic motion Circular motion Random motion Translational motion. What does the speed of sound depend on?
The wavelength of the wave The size of the medium The frequency of the wave The properties of the medium. The volume of the gas The flammability of the gas The mass of the gas The compressibility of the gas.
Previous Next. In cartoons depicting a screaming person or an animal making a loud noise , the cartoonist often shows an open mouth with a vibrating uvula, the hanging tissue at the back of the mouth, to suggest a loud sound coming from the throat Figure 2. The relevant physical quantity is sound intensity, a concept that is valid for all sounds whether or not they are in the audible range. Intensity is defined to be the power per unit area carried by a wave. Power is the rate at which energy is transferred by the wave.
The intensity of a sound wave is related to its amplitude squared by the following relationship:. We are using a lower case p for pressure to distinguish it from power, denoted by P above. This relationship is consistent with the fact that the sound wave is produced by some vibration; the greater its pressure amplitude, the more the air is compressed in the sound it creates. Figure 2. Graphs of the gauge pressures in two sound waves of different intensities.
The more intense sound is produced by a source that has larger-amplitude oscillations and has greater pressure maxima and minima. Because pressures are higher in the greater-intensity sound, it can exert larger forces on the objects it encounters. Sound intensity levels are quoted in decibels dB much more often than sound intensities in watts per meter squared.
Decibels are the unit of choice in the scientific literature as well as in the popular media. The reasons for this choice of units are related to how we perceive sounds. How our ears perceive sound can be more accurately described by the logarithm of the intensity rather than directly to the intensity.
In particular, I 0 is the lowest or threshold intensity of sound a person with normal hearing can perceive at a frequency of Hz. Sound intensity level is not the same as intensity. The units of decibels dB are used to indicate this ratio is multiplied by 10 in its definition. The bel, upon which the decibel is based, is named for Alexander Graham Bell, the inventor of the telephone. That is, the threshold of hearing is 0 decibels. Table 1 gives levels in decibels and intensities in watts per meter squared for some familiar sounds.
One of the more striking things about the intensities in Table 1 is that the intensity in watts per meter squared is quite small for most sounds. The ear is sensitive to as little as a trillionth of a watt per meter squared—even more impressive when you realize that the area of the eardrum is only about 1 cm 2 , so that only 10 —16 W falls on it at the threshold of hearing! Air molecules in a sound wave of this intensity vibrate over a distance of less than one molecular diameter, and the gauge pressures involved are less than 10 —9 atm.
Another impressive feature of the sounds in Table 1 is their numerical range. Sound intensity varies by a factor of 10 12 from threshold to a sound that causes damage in seconds.
You are unaware of this tremendous range in sound intensity because how your ears respond can be described approximately as the logarithm of intensity. Thus, sound intensity levels in decibels fit your experience better than intensities in watts per meter squared. The decibel scale is also easier to relate to because most people are more accustomed to dealing with numbers such as 0, 53, or than numbers such as 1.
For example, a 90 dB sound compared with a 60 dB sound is 30 dB greater, or three factors of 10 that is, 10 3 times as intense. Another example is that if one sound is 10 7 as intense as another, it is 70 dB higher.
See Table 2. Air has a density of 1. Calculate to find the sound intensity level in decibels:. This 87 dB sound has an intensity five times as great as an 80 dB sound. So a factor of five in intensity corresponds to a difference of 7 dB in sound intensity level.
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