Physical Principles of Sound introduction.
Physical Principles of Sound depends on Wavelength, Amplitude, Frequency, Time period and Velocity. It also Varies with mechanical waves, periodic waves, Sound waves etc. Ripples in a pond, musical sounds or seismic tremors triggered by an earthquake—all these exhibit a wave phenomenon. Waves can occur whenever a system is disturbed from equilibrium and when the disturbance can travel or propagate from one region to other.
As a wave propagates, it carries energy. The energy of seismic waves can be so high that it can break the earth’s crust. Waves in a string play an important role in music. When a musician strums a wave or bows a violin, he makes waves that travel in opposite directions along the instrument’s strings. What happens when those oppositely directed waves overlap is called interference. Not all waves are mechanical in nature. Electromagnetic waves like light, radiowaves, infrared and ultraviolet radiations, etc. can propagate in vacuum or empty spaces, where there is no medium.
Mechanical Waves .
A mechanical wave is a disturbance that travels through some material or substance called the medium for the wave. As the wave travels through the medium, the particles that make up the medium undergo displacements of various kinds, depending on the nature of the wave. If the displacements of the medium are perpendicular or transverse to the direction of travel of the wave along the medium, it is called a transverse wave.
Examples can be seen in a string or rope. If the displacements of the medium are parallel or longitudinal to the direction of travel of the wave along the medium, it is called a longitudinal wave. Examples can be seen in a fluids (liquid) or gases. If the displacements of the medium are both parallel and perpendicular to the direction of travel of the wave along the medium, it is called a mixed wave. Examples can be seen in a water canal. These examples have three on common.
1. In each case the disturbance travels or propagates with a definite speed through the medium. This speed is called the speed of propagation, or simply the wave speed. It is determined in each case by the mechanical properties of the medium.
2. The medium itself does not travel through space; its individual particles undergo back-and-forth or up-and-down motions around their equilibrium positions. The overall pattern of the wave disturbance is what travels.
3. To set any of these systems into motion, we have to put in energy by doing mechanical work on the system. The wave motion transports this energy from one region of the medium to another. Waves transport energy, but not matter, form one region to another.
Periodic Waves .
The transverse wave on a stretched string is an example of a wave pulse. The hand shakes the string up and down just once, exerting a transverse force on it. The result is a single “wiggle” or pulse that travels along the length of the string. The tension in the string restores its straight line shape once the pulse has passed. When we give the free end of the string a repetitive or periodic motion, then each particle in the string also undergoes periodic motion as the wave propagates and we have a periodic wave.
As the wave moves, any point on the string oscillates up-and-down about its equilibrium position with simple harmonic motion. When a sinusoidal wave passes through a medium, every particle in the medium undergoes a simple harmonic motion with the same frequency. For a periodic wave, the shape of the string at any instant is a repeating pattern.
The length of one complete wave pattern is the distance from one crest to the next or from one trough to the next or from any point to the corresponding point on the next repetition of the wave shape. This is called wavelength of the wave which is denoted by λ (Greek letter lambda). The wave pattern travels with a constant speed ν and advances a distance of one wavelength λ in a time interval of one period T. The speed of propagation equals the product of wavelength and frequency. The frequency is a property of the entire periodic wave because all points on the string oscillate with the same frequency f.
Sound Waves .
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.
Propagation of sound .
Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. During propagation, waves can be reflected, refracted, or attenuated by the medium.
The behavior of sound propagation is generally affected by three things :-
1. A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium.
2. The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving the sound is further transported.
3. The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.
When sound is moving through a medium that does not have constant physical properties, it may be refracted (either dispersed or focused).
Perception of sound .
The perception of sound in any organism is limited to a certain range of frequencies. For humans, hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz), although these limits are not definite. The upper limit generally decreases with age. Other species have a different range of hearing. For example, dogs can perceive vibrations higher that 20k Hz, but are deaf to anything below 40 Hz.
As a signal perceived by one of the major senses, sound is used by many species for detecting danger, navigation, predation, and communication. Earth’s atmosphere, water and virtually any physical phenomenon, such as fire, rain wind or earthquake, produces (and is characterized by) its unique sounds. Many species, such as frogs, birds, marine and terrestrial mammals, have also developed special organs to produce sound.
In some species, these produce song and speech. Furthermore, humans have developed culture and technology (such as music, telephone and radio) that allows them to generate, record, transmit and broadcast sound. The scientific study of human sound perception is known as psychoacoustics.
Physics of Sound .
The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter: solid, liquid or gases. The matter that supports the sound is called the medium. Sound cannot travel through a vacuum.
Longitudinal and transverse waves .
Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above. The horizontal axis represents time. Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves. Through solids, however, it can be transmitted as both longitudinal waves and transverse waves.
Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction, while transverse waves (in solids) are waves of alternating shear stress at right angle to the direction of propagation. Matter in the medium is periodically displaced by a sound wave, and thus oscillates.
The energy carried by the sound wave converts back-and-forth between the potential energy of the extra compression (in case of longitudinal waves) or lateral displacement strain (in case of transverse waves) of the matter and the kinetic energy of the oscillations of the medium.
Sound Wave Properties and Characteristics .
Sound waves are often simplified to a description in terms of sinusoidal plane waves, which are characterized by these generic properties: Frequency, or its inverse, the period.
- Wavelength.
- Wave number.
- Amplitude.
- Sound pressure.
- Sound intensity.
- Speed of sound.
- Direction.
Sometimes speed and direction are combined as a velocity vector; wave number and direction are combined as a wave vector. Transverse waves, also known as shear waves, have the additional property, polarization, and are not a characteristic of sound waves.
Speed of Sound .
The speed of sound depends on the medium the waves pass through, and is a fundamental property of the material. The physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature.
In 20°C (68°F) air at the sea level, the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph). In fresh water, also at 20°C, the speed of sound is approximately 1,482 m/s (5, 335 km/h; 3,315 mph). In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph).
Thanks for Visiting us.
