A project on sound by nikund

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1. A project on sound Made by-Nikund Jain Class-9 th -C Roll no.-12

2. WHAT IS SOUND ?... Sound is a form of energy . It is that form of energy which makes us hear.   S ound  is a  vibration  that propagates as a typically audible  mechanical wave  of  pressure  and  displacement , through a  transmission medium  such as air or water . In our daily lives we observe many examples such as chirping of birds , mixer-grinder , stereo-system , violin ,guitar , veena, etc.

3. Sound is transmitted through gases, plasma, and liquids as  longitudinal waves , also called  compression  waves. It requires a medium to propagate. 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. Longitudinal and transverse waves

4. Properties of sound waves   There are many complexities relating to the transmission of sounds, at the point of reception (i.e. the ears), sound is readily dividable into two simple elements: pressure and time .  which are characterized by these generic properties: Frequency , or its inverse, the  Wavelength Amplitude Sound pressure  /  Intensity Speed of sound Direction

5. FREQUENCY Frequency  is the number of occurrences of a repeating event per unit  time . It is also referred to as  temporal frequency. The  period  is the duration of time of one  cycle  in a repeating event, so the period is the  reciprocal  of the frequency .  For example, if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second . Frequency is an important parameter used in science and engineering to specify the rate of  oscillatory  and  vibratory phenomena , such as mechanical vibrations,  audio  ( sound ) signals,  radio waves , and  light .

6. AMPLITUDE Peak-to-peak amplitude is the change between peak (highest amplitude value) and  trough  (lowest amplitude value, which can be negative). With appropriate circuitry, peak-to-peak amplitudes of electric oscillations can be measured by meters or by viewing the waveform on an  oscilloscope . This remains a common way of specifying amplitude, but sometimes other measures of amplitude are more appropriate.

7. INTENSITY Sound intensity  also known as  acoustic intensity  is defined as the Energy carried by the sound waves per unit area. The  SI unit  of intensity, which includes sound intensity, is the  watt  per square meter (W/m 2 ). One application is the noise measurement of sound  intensity  in the air at a listener's location as a sound energy quantity . Sound intensity is not the same physical quantity as  sound pressure . Hearing is directly sensitive to sound pressure which is related to sound intensity. 

8. SPEED OF SOUND The  speed of sound  is the distance travelled per unit time by a  sound wave  as it propagates through an  elastic  medium. In dry  air  at 20 °C (68 °F), the speed of sound is 343.21 metre per second  . The speed of sound in an  ideal gas  depends only on its temperature and composition. The speed has a weak dependence on frequency and pressure in ordinary air, deviating slightly from ideal behavior . Sound waves in solids are composed of compression waves (just as in gases and liquids), but there is also a different type of sound wave called a  shear wave , which occurs only in solids. 

9. A distinct use of the term  sound  from its use in physics is that in physiology and psychology, where the term refers to the subject of  perception  by the brain. The field of  psychoacoustics  is dedicated to such studies. Historically the word "sound" referred exclusively to an effect in the mind. Webster's 1947 dictionary defined sound as: "that which is heard; the effect which is produced by the vibration of a body affecting the ear ."  This meant (at least in 1947) the correct response to the question: " if a tree falls in the forest with no one to hear it fall, does it make a sound? " was "no". However, owing to contemporary usage, definitions of sound as a physical effect are prevalent in most dictionaries Perception of sound

10. Characteristic of sound waves There are four experimentally separable ways in which sound waves are analyzed. They are : Pitch Duration Loudness Timbre

11. pitch Pitch  is perceived as how "low" or "high" a sound is and represents the cyclic, repetitive nature of the vibrations that make up sound. For simple sounds, pitch relates to the frequency of the slowest vibration in the sound (called the fundamental harmonic). In the case of complex sounds, pitch perception can vary. Sometimes individuals identify different pitches for the same sound, based on their personal experience of particular sound patterns.

12. duration Duration  is perceived as how "long" or "short" a sound is and relates to onset and offset signals created by nerve responses to sounds. The duration of a sound usually lasts from the time the sound is first noticed until the sound is identified as having changed or ceased .  Sometimes this is not directly related to the physical duration of a sound

13. loudness Loudness  is perceived as how "loud" or "soft" a sound is and relates to the totaled number of auditory nerve stimulations over short cyclic time periods, most likely over the duration of theta wave cycles . This means that at short durations, a very short sound can sound softer than a longer sound even though they are presented at the same intensity level. Past around 200 m/s this is no longer the case and the duration of the sound no longer affects the apparent loudness of the sound. 

14. timbre{quality} Timbre  is perceived as the quality of different sounds and represents the pre-conscious allocation of a sonic identity to a sound. This identity is based on information gained from frequency transients, noisiness, unsteadiness, perceived pitch and the spread and intensity of overtones in the sound over an extended time frame .  The way a sound changes over time provides most of the information for timbre identification. Even though a small section of the wave form from each instrument looks very similar differences in changes over time between the clarinet and the piano are evident in both loudness and harmonic content.

15. noise Noise  is a term often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal. However, in sound perception it can often be used to identify the source of a sound and is an important component of timbre perception

16. echo E cho  is a  reflection  of sound that arrives at the listener with a delay after the direct sound. The delay is proportional to the distance of the reflecting surface from the source and the listener. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single reflection of the sound  .

17. reverberation  A reverberation, or  reverb , is created when a sound or signal is reflected causing a large number of reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and air . This is most noticeable when the sound source stops but the  reflections  continue, decreasing in  amplitude , until they reach zero amplitude.

18. sonar Sonar  (originally an  acronym  for  SO und  N avigation  A nd  R anging) is a technique that uses  sound  propagation (usually underwater, as in  submarine navigation ) to  navigate , communicate with or detect objects on or under the surface of the water, such as other vessels .  Sonar may be used as a means of  acoustic location  and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of  radar . Sonar may also be used in air for robot navigation.

19. ultrasonic Ultrasound  is  sound waves  with  frequencies  higher than the upper audible limit of human  hearing . Ultrasound is no different from 'normal' (audible) sound in its physical properties, except in that humans cannot hear it. This limit varies from person to person and is approximately 20  kilohertz  (20,000 hertz) in healthy, young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz. Ultrasound is used in many different fields. Ultrasonic devices are used to detect objects and measure distances.  Ultrasound imaging  or sonography is often used in  medicine . 

20. infrasonic I nfrasound , sometimes referred to as  low-frequency sound , is sound that is lower in frequency than 20  Hz  or cycles per second, the "normal" limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the  sound pressure  must be sufficiently high. The ear is the primary organ for sensing infrasound, but at higher intensities it is possible to feel infrasound vibrations in various parts of the body. This frequency range is utilized for monitoring earthquakes, charting rock and petroleum formations below the earth, and also in  ballistocardiography  and seismocardiography to study the mechanics of the heart.

21. Sonic boom A  sonic boom  is the sound associated with the  shock waves  created by an object traveling through the air faster than the speed of sound. Sonic booms generate enormous amounts of  sound  energy, sounding much like an  explosion . The crack of a supersonic  bullet  passing overhead or the crack of a  bullwhip  are examples of a sonic boom in miniature.

22. Human ear The  ear  is the  organ  of  hearing  and, in mammals,  balance . In mammals, the ear is usually described as having three parts—the  outer ear ,  middle ear  and the  inner ear . The outer ear consists of the  pinna  and the  ear canal . Since the outer ear is the only visible portion of the ear in most animals, the word "ear" often refers to the external part alone . The middle ear includes the  tympanic cavity  and the three  ossicles . The inner ear sits in the  bony labyrinth , and contains structures which are key to several senses: the  semicircular canals , which enable balance and eye tracking when moving; the  utricle  and  saccule , which enable balance when stationary; and the  cochlea , which enables hearing. The ears of  vertebrates  are placed somewhat symmetrically on either side of the head, an arrangement that aids  sound localization .