Acoustic Waves in Physics
An acoustic wave can simply be described as a longitudinal wave. A longitudinal wave is a wave that vibrates and moves in the direction of its propagation. This means the medium is either in the same or opposite direction of the way the wave travels. Acoustic waves are a form of Mechanical longitudinal waves; these waves are otherwise known as compression waves or compressional waves. Compressional waves obviously produce compression, decompression, and rarefaction to travel.
In Physics, the acoustic wave has an equation to describe the evolution of acoustic pressure and particle velocity as a function. The general equation is:
Acoustic waves have multiple equations, but this version is the simplified form. In a simplified acoustic wave equation there is only one spatial dimension. In other more complex equations there is a possibility of two or maybe even three dimensions. [5] The letter “p” in the general form equation pictured above is to show the acoustic pressure . The letter “c” represents the speed of sound. Both acoustic pressure and speed of sound are the key ingredients to describing the behavior of sound in matter.
A solution for this particular acoustic wave equation is:
“F” and “g” both show two twice-differentiable functions, and “c” again, is the speed of sound. [5]
After reading the first paragraphs you may be wondering why are acoustic waves so important in normal life or “why would I ever need this equation?’ Acoustic waves are important because sound is all around us. When you think of the word “acoustic” a few words may come to mind. Guitars, stereos, and many other items involve acoustic waves. For example, when the bass on a stereo is turned all the way up you m...
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...smits the waves from one direction but as soon as it reflects it blocks them from the other. [1]
Many people hear both terms, acoustic and sound waves and think they are basically the same. That seems to be untrue because sound waves do not have polarization. [3] The reason why they don’t have polarization is because sound waves oscillate in the same directions they move. This means sound waves cannot reflect while acoustic waves can. For example, when you are in a domed shaped building the acoustics allow you to hear an echo or a projection of a noise from the other side of the room.
There is not many information on acoustic waves but it was interesting researching this topic. The little that I found was really cool and I’m glad I did this essay on such a topic. Acoustic waves are all around us and are important in science.
If you put your finger gently on a loudspeaker you will feel it vibrate - if it is playing a low note loudly you can see it moving. When it moves forwards, it compresses the air next to it, which raises its pressure. Some of this air flows outwards, compressing the next layer of air. The disturbance in the air spreads out as a travelling sound wave. Ultimately this sound wave causes a very tiny vibration in your eardrum - but that's another story.
As a part of this longitudinal sound wave, the particles vibrate back and forth in a direction parallel to the direction of energy. Since the air molecules always return to their original position, they have no net displacement. When the vibrating molecules of air have to escape somewhere, this is where the sound hole comes into play. The air escapes through it and this is where the sound is projected. When all this occurs, it’s called the Helmholtz resonance (Wolfe).
To understand what an echo is, you first have to understand what sound is. In Webster’s Fourth Edition College Dictionary, sound is “vibrations in air, water, etc. that stimulate the auditory nerves and produce the sensation of hearing.” Vibrations through the air can be thought of as oscillation of molecules. As the molecules oscillate, they pass energy on to surrounding molecules, and those molecules pass energy on to other surrounding molecules. This is how sound travels, and the oscillation of the molecules is often referred to as sound waves.
Sound is a type of longitudinal wave that originates as the vibration of a medium (such as a person’s vocal cords or a guitar string) and travels through gases, liquids, and elastic solids as variations of pressure and density. The loudness of a sound perceived by the ear depends on the amplitude of the sound wave and is measured in decibel, while its pitch depends on it frequency measured in hertz, (Shipman-Wilson-Higgins, 2013).
Ultrasound is sound waves that have a frequency above human audible. (Ultrasound Physics and Instrument 111). With a shorter wavelength than audible sound, these waves can be directed into a narrow beam that is used in imaging soft tissues. As with audible sound waves, ultrasound waves must have a medium in which to travel and are subject to interference. In addition, much like light rays, they can be reflected, refracted, and focused.
As said above, both light and sound waves have to do with interference. In sound, interference affects both the loudness and amplitude. When two waves’ crests overlap, the amplitude increases. The same is true with the troughs of the waves, which decrease the amplitude.
Waves can be described as a transfer of energy. They can occur in one, two or three dimensions, depending on the nature of the wave and medium. Waves can be classified as either mechanical or electromagnetic. Mechanical waves require a medium and can be either transverse or longitudinal. Electromagnetic waves do not require a medium and are all transverse. Figure 1.a. shows the image of a transverse wave, figure 1.b. shows the image of an electromagnetic wave.
Tillery, B. (2012). Wave Motions and Sound. Physical science (9th ed., pp. 115-134). New York,
Sound is made when something vibrates. The vibrating body causes the medium water and air around it to vibrate. Vibrations in the air are traveling longitudinal waves, that we can hear. Sound waves are in areas of high and low pressure called compressions and rarefactions. Lighter areas are low pressure rarefactions and darker areas are high pressure compressions. The wavelength and the speed of the wave figures the pitch, or frequency of sound. Wavelength, frequency, and speed are related by the equation speed means wavelength. Since sound travels at 343 meters per second at standard temperature and pressure speed is a constant. The longer the wavelength, the lower the pitch. The height of the wave is its amplitude. The amplitude shows how
Compared to radio waves used in terrestrial sensor networks, which would have very high attenuation underwater, acoustic waves has better propagation characteristics in water, making it the preferred method for underwater communications. Hence acoustic channel is used as a link for communication in underwater sensor...
Sonar which is short for Sound Navigation and Ranging, uses sound waves to calculate distances from objects in water. This information can be used to produce maps of lake bed or sea floor. Sound waves are produced from an active sonar transducer. The sound wave travels outwards from the transducer and bounces off objects on the sea floor. These waves come back to the transducer and if it is specially equipped can measure the change in strength and time it takes to return with a computer. The time between the emission and reception of the wave will make it possible to calculate the distance and angle of the object that the sound wave bounced off of. (NOAA, 2014.).
Compression and rarefaction of particles forming sound waves. Retrieved 23/02/14 from Popular Science Monthly Volume 13
The Physics Classroom. "Frequency and Period of a Wave." Physic Classroom. The Physics Classroom, 1996. Web. 28 Nov. 2013. .