Physics Classroom says:
Sound is produced by a vibrating object. The vibrating object may be one's vocal cords, the diaphragm of a speaker, the vibrations of a drumhead, or a plucked guitar string.
As a guitar string vibrates with a given wave pattern, it disturbs the surrounding air and forces it to vibrate as well. But the vibrating string also sets the guitar's sound box into vibrations of the same frequency. As the sound box vibrates, an even greater quantity of air is forced to vibrate. One vibrating air particle can force another neighboring air particle to vibrate. These vibrations are sent by particle-to-particle interactions from the source (guitar string) to nearby observers.
To learn more about sound waves, visit The Physics Classroom Tutorial.
Physics Classroom says:
The diaphragm of an audio speaker vibrates in and out. These vibrations produce sound waves by disturbing surrounding air particles and forcing them to vibrate as well.
We can't see the vibrating air particles. It is even difficult to see the speaker diaphragm vibrating. The placement of salt crystals on the diaphragm and the use of a high speed video camera produces convincing evidence that the diaphragm and salt (and surrounding air particles) are vibrating. Press the Play button for the video at the right and enjoy the sight of vibrating salt crystals in slow motion.
To learn more about sound waves, visit The Physics Classroom Tutorial.
Physics Classroom says:
Not all vibrating objects produce waves whose frequencies fall into the range of human's ability to hear. For example, bats produce sound waves that are of such high frequencies that the human ear cannot detect it. These types of waves are known as ultrasound waves.
Bats emit the ultrasound waves as rapid pulses. High frequency waves are less likely to diffract or bend around an object in its path. Instead, the waves reflect off the objects, allowing the bats to hunt and navigate by echolocation. Some bats, known as Doppler bats, are capable of detecting the speed and direction of any moving objects by monitoring the changes in frequency of the reflected pulses.
Physics Classroom says:
Bats aren't the only creatures that depend on vibrational waves that fall outside of the human range of hearing. Elephants produce waves that have frequencies the fall below human's audible range of hearing. These low frequency waves are known as infrasonic waves.
For years, researchers of elephants in the wild had been perplexed by the ability of elephants to allegedly communicate across large distances to other members of the herd. Scientists now know that this communication occurs by means of infrasound. Using frequencies as low as 14 Hz, elephants communicate to one another across distances as large as 4 kilometers. The low frequency infrasound is capable of diffracting (bending around) obstacles in its path in order to carry the further distances. This explains the highly synchronized movements of elephants that had perplexed scientists for years.
To learn more about sound frequencies, visit The Physics Classroom Tutorial.
Physics Classroom says:
The water goblet trick just discussed is the basis of today's modern day glass harmonica players. An offshoot of Ben Franklin's glass harmonica, today's players use water goblets partially filled with water. By adjusting the amount of water in each goblet, the musician can tune the instrument to produce the desired pitch. How does it work?
The speed at which vibrations travel through the glass is directly related to the pitch that is heard produced the vibrating glass. The speed can be increased by emptying water from the goblet. The water serves to decrease the speed of vibrations. So reducing the amount of water increases the speed at which vibrations travel through the glass, thus increasing the pitch that is heard from its vibrations.
Physics Classroom says:
Tuning forks produce sound waves by the vibrations of its tines. As the tines of the fork vibrate back and forth, air particles surrounding the tines are disturbed and forced into vibrating at the same frequency as the tines. This produces a sound wave which nearby observers hear.
Different tuning forks have different natural frequencies at which they vibrate. The frequency of the tuning fork is primarily dependent upon the length of the tines. Longer tines vibrate at lower frequencies, thus producing lower pitches.
To learn more about the natural frequencies of vibrating objects, visit The Physics Classroom Tutorial.
Physics Classroom says:
A string, such as a guitar string, will vibrate when plucked. While it has a set of natural frequencies at which it will vibrates, it most often vibrates with the lowest frequency of the set - known as the fundamental frequency. The actual frequency value of the fundamental is dependent upon how tight the string is pulled (tension), the linear density (thickness and material) of the string, and the length of the string. Guitarists have control over all three variables. By tightening and loosening the string, fingering it at a given fret position, and choosing which of the six strings are plucked, a guitarist can control the frequency of the sound that is produced.
To learn more about the physics of guitar strings, visit The Physics Classroom Tutorial.
Physics Classroom says:
The photo at the right depicts flames emerging from a hollow aluminum pipe. Holes have been drilled into the aluminum and an audio speaker inserted at one end. A gas inlet tube is inserted into the opposite end. The methane gas exits the holes and is lit to produce small flames. Using a frequency generator, the audio speaker is forced to vibrate at one of the natural frequencies of the tube. A standing wave pattern of nodal and anti-nodal regions is produced within the tube. This forces the flames to be higher in some regions and lower in other regions.
This photo demonstrates that even a column of air can vibrate to produce a sound wave. Each natural frequency at which it vibrates is associated with a standing wave pattern.
To learn more about sound and standing wave patterns, visit The Physics Classroom Tutorial.
Physics Classroom says:
The infamous Blue Man Group (BMG) demonstrates on a nightly basis the physics associated with vibrating objects. Using an odd collection of PVC pipe and associated fittings, BMG both amazes and amuses the crowd with a dashing display of drumming. A tap, a clap or a rap upon the PVC forces it to vibrate at its natural frequency. The air inside the pipe resonates with it, thus amplifying the sound. By changing the length of the PVC. the BMG are able to control the frequency of the sound. Like the tuning forks discussed earlier, a longer pipe will vibrate to produce a lower pith and a shorter pipe will vibrate to produce a higher pitch. This is another example of physics for better living.
To learn more about resonating instruments, visit The Physics Classroom Tutorial.
Physics Classroom says:
Observe the variety of lengths of organ pipe in this auditorium. Each of these organ pipes produces a vibrates with a different natural frequency. The natural frequency is determined in part by the length of the air column inside the organ pipe. The relationship between frequency and length is so predictable that a simple equation can be used to express it. Not surprisingly, organ pipe manufacturers heed the wisdom of the equation in the construction of their organ pipes. The result - beautiful music fills the hall. This is one more example of physics for better living.
To learn more about the physics of resonating air columns, visit The Physics Classroom Tutorial.
Physics Classroom says:
There's no more need to be feeling down and blue. A little understanding of physics will make anyone's life a whole lot richer. The world is filled with physics. And the world of sound is no different.
We hope you have enjoyed our gallery on Sound and Music. Additional galleries can be found at The Physics Classroom's Galleries page.
And to learn more about the physics in the world around us, visit The Physics Classroom Tutorial.
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