They cause the air molecules to bunch together in high points and spread out in low points. This creates rolling peaks and valleys. Each compression and rarefaction takes one cycle.
Initiation Sound Waves
A sound wave is a mechanical sound waves disturbance from a state of equilibrium that propagates through an elastic material medium. Its basic physical attributes are its frequency, amplitude, and temporal variation. Frequency is the number of times per second that the vibratory pattern oscillates; amplitude is the size of the displacement of particles from their equilibrium positions; and temporal variation is the variations in the time interval between consecutive vibrations (also known as a period or cycle).
For a sound to be heard, the vibrations must be transmitted and converted into a neural-electrical signal that is processed by the human ear. The ear is an extremely efficient transducer that changes sound pressure in air into information the brain can process. This processing occurs in the external ear, middle ear, inner ear, and brainstem. The result is the perception of sound as speech, music, or noise.
The initiation of a sound wave occurs when a vibrating object, such as a speaker or plucked guitar string, causes the surrounding air molecules to vibrate. These vibrations, in turn, cause other air molecules to vibrate, and so on. This continues in a circular fashion, transmitting the vibrations to other nearby air molecules until they reach the eardrum—the boundary between the outer and middle ear portions of the sound waves head. The eardrum then receives a fluctuating net force that triggers the three small bones in the middle ear, which, in turn, produces vibration in tiny cells inside the cochlea. This process then converts the nerve signals into the perception of sound.
There are many types of waves that move through a medium, including longitudinal, mechanical, and pressure. Longitudinal waves are sequences of compressions and rarefactions that travel in the direction the energy is propagating. This is familiar to anyone who has played with a slinky toy, where one can observe a repeated back-and-forth motion that creates the characteristic sound wave pattern.
The speed at which a sound travels is related to the speed at which the particles in the medium are vibrating and the medium’s density. The velocity of a sound is also determined by its wavelength, which can be expressed as the distance between a peak and the start of the next trough. It is often convenient to use the term wavelength in place of frequency when referring to sounds, because frequencies are sound waves usually measured in units of seconds per cycles or periods, commonly referred to as hertz (Hz).
Transmission Sound Waves
When a sound wave hits a surface, it can react in several different ways. It can transmit through the surface, reflect off of it or be absorbed by it. In some cases, it may combine all of these mechanisms to create a diffuse field that can be heard from a large distance.
The first thing that occurs when a sound wave hits a surface is that it causes the particles in the medium it is traveling through to vibrate. This vibration passes kinetic energy to the particles that are further away from the source, and then back again as the wave moves forward. This process is what makes sounds louder or quieter.
As the sound wave travels sound waves through the medium, it will generate compressions and rarefactions. Compressions occur when the molecules move closer together, creating regions of high pressure, while rarefactions are created when the particles move farther apart, creating regions of low pressure. This is the same phenomenon that produces ripples on a lake, or the vibrations of a tuning fork.
Since sound waves are mechanical waves, they can travel through any type of matter, including solids, liquids and gases. The properties of the medium that the wave passes through, however, can affect the speed at which it travels.
For example, a sound wave will travel faster through a solid than it will through a liquid or gas. This is because the molecules in a solid are closer together and more tightly bonded than those in a liquid or gas.
The speed at which a sound wave travels is also affected by the elastic properties and density of the medium it is in. The higher the elastic properties of a material, the less it will deform when a force is applied to it. The denser a medium is, the slower it will travel.
Propagation Sound Waves
Sound moves through a medium sound waves such as air or water, carrying energy and information via oscillations of pressure and particle displacement. The movement of the particles is what we perceive as a wave. As the particles move, they alternately push each other closer together (compression) and pull them further apart (rarefaction). This process continues from one particle to the next, transferring the energy of the wave. This is what we call propagation, and it is the reason that a sound wave can travel over long distances.
Sound waves can take on different shapes depending on their characteristics and the properties of the medium through which they are traveling. A sound wave that travels through a medium with a low density will appear as a plane wave rather than as a circular or spherical wave. A plane wave is characterized by rolling peaks and valleys. When the wave moves faster, these peaks and valleys will form closer together. A wave that moves slower will cause the peaks and valleys to spread out.
A wave can also change shape when it passes from a material with low shear stiffness to a material with high shear stiffness. This is called refraction and is a common occurrence in physics. The waves can also bend when they pass around an obstacle or through an opening in an obstacle. This is known as diffraction and can be demonstrated in a physics laboratory by using a lens-shaped balloon filled with carbon dioxide to focus the energy of the sound into a narrow beam.
As the wave propagates, the pressure sound waves variation repeats itself over a fixed distance known as its wavelength. Each repetition takes a specific time, which is known as its frequency and measured in cycles per second or Hertz (abbreviated Hz). The amplitude of the wave is the maximum amount that the particle displacement varies during one cycle.
The speed at which the wave travels through a medium depends on its density and its refractive index. Air is the fastest medium for sound to travel, with a speed of about 340 meters per second. Sound can travel even more quickly through other materials, such as steel, although the speed is considerably less. The ability of sound to move so rapidly enables us to transmit a great deal of information and perform a number of important tasks, such as lithotripsy, a procedure that breaks up kidney stones.
Interference Sound Waves
In the real world sound waves interact with each other in interesting ways. Two identical wave swells that meet at the same point in the medium can either reinforce each other and create a larger wave or cancel each other out and produce a smaller one. These two types of interaction are called constructive and destructive interference respectively. The occurrence of each is determined by the phase relationship between the two waves. If they are in phase, then their crests and troughs align to create a larger wave. If they are out of phase, then their crests and droughs are offset from each other and their amplitude is reduced.
The varying effects of constructive and destructive interference give rise to all kinds of sounds in the real world. If a wave is being sound waves played back through an echo chamber, for instance, the waves of reflected energy will interfere with each other in a way that causes the sound to cycle up and down in intensity. This is known as beating and it gives the impression that a continuous stream of loud and soft sounds is being produced.
This type of interference is also observed when two different frequencies of a sound wave interfere with each other. The result is a sound wave with a frequency equal to the average of the two frequencies. The alternating cycles of constructive and destructive interference produce a beat frequency which can be heard as a pulsing sound.
More Words
All kinds of waves can interfere with each other but to cause a change in amplitude they must have the same polarization. This is the opposite of what happens with light, which can be polarized in two distinct ways: one direction and the other.
The polarization of a medium sound waves can be altered by introducing other waves of the same frequency into the medium. In fact, if two waves of the same frequency interfere with each other with exactly the same polarization, they will add together to produce a single wave with twice the amplitude of the individual waves. This effect can be used to produce very thin fringes on the surface of a liquid or gas, for instance.