Chapter - 13, Sound, Science, Class 8
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The document discusses the nature of sound, explaining that it is a form of energy produced by vibrating objects and that it requires a medium to propagate. It outlines how humans produce sound through their vocal cords and explores sound properties, including amplitude, frequency, and the difference between noise and music. Additionally, the document addresses noise pollution, its causes and effects on health, as well as potential prevention strategies.
Chapter - 13, Sound, Science, Class 8
- 1. Chapter – 13 Sound By Shivam Parmar (Entrepreneur) Email for more PPTs at a very reasonableprice. Email: parmarshivam105@gmail.com
- 2. WHAT IS SOUND? • A sound is a form of energy that is produced when air molecules vibrate in a particular pattern called waves. Hence, the sound is a wave. • Vibration can be described as a back and forth motion of an object. • Depending upon the vibrations, a sound is produced. Sound cannot be produced without any vibration.
- 3. INTRODUCTION TO SOUND • The sound is produced by vibrating objects. • They travel from one place to another in the form of waves. Hence, the name sound waves.
- 5. SOUND PROPERTIES • Sound needs a medium to propagate. The matter or material through which sounds propagates is called a medium. • Sound cannot travel in a vacuum, as it lacks any medium of transmission. • The moon does not have an atmosphere, hence, you can hear on the moon.
- 6. HOW DO HUMANS PRODUCE SOUND? • Human beings have a voice box or larynx which is present in their throat on the upper side of the windpipe. • The larynx has two vocal cords which have a narrow slit between them so that air can pass through it. • As the lungs throw the air out of the windpipe, it passes through the slit and hence allows the production of sound as the vocal cords start vibrating.
- 7. • The vocal cord muscles also play a role in the production of sound. • Their thickness and tightness describe the quality or type of the voice a person has. • The vocal cords in males are of length 20 mm and females have 15mm long vocal cords. Children, on the other hand, have very short length vocal cords. Hence, the voices, their quality and their type are always different in women, men and children.
- 8. HOW SOUND PROPAGATE IN A MEDIUM? • Sound needs some vibration of molecules to travel. • Solids, liquids and gases all have molecules present in them which allow the propagation of sound. • These molecules or particles in solids, liquids and gases are packed in varied ways. • Solids have tightly packed particles in them and hence they allow fast propagation of sound through them.
- 9. Liquids have slightly loosely packed particles and hence it takes a little time for sound to travel in water or through a liquid. Gases have completely loosely packed particles and hence sound takes the mosttime in travelling through the air.
- 10. SOUNDS BY HUMANS • We know that sounds are produced as waves in the air or any other medium. • As these sound waves travel to our ears they convert them into electrical signals or messages that our brain can understand. • Our ears have a special structure that allows this function.
- 11. THERE ARE THREE MAJOR PARTS OF THE HUMAN EAR 1. The Outer Ear 2. The Middle Ear 3. The Inner Ear
- 13. AMPLITUDE, TIME PERIOD AND FREQUENCY • The magnitude of disturbance in the medium on either side of the mean value is called as Amplitude(A).Larger the amplitude, louder the sound. • The number of oscillations per second is called frequency. Expressed in Hertz (Hz). • Time taken for one complete oscillation to travel across a point. • T = 1/f.(Seconds)
- 14. THE LOUDNESS OF A SOUND • The loudness of a sound depends upon the amplitude of the sound. • The higher the amplitude, the higher is the displacement of the particles and the higher is the loudness of the sound. • The loudness of the sound is directly proportional to the square of its amplitude. • The SI unit for measuring the loudness of a sound in decibels (dB).
- 16. PITCHOF THE SOUND • Every person has a different sound quality. • Also, every musical instrument vibrates to produce a different kind of sound. This quality of sound is characterized by its Different quality of sounds may have same pitch and loudness. • The pitch of a sound depends upon the frequency of the sound wave. • The pitch would be higher if the frequency of the sound is high.
- 17. AUDIBLE AND INAUDIBLE SOUNDS • Audible range = 20Hz to 20kHz known as the Sonic range. • Below 20 Hz (inaudible) → Infrasonic range • Above 20 kHz (inaudible) → Ultrasonic range
- 18. NOISE AND MUSIC • Noise can be regarded as an unpleasant sound. Noise consists of sound waves of varied frequencies which have no particular periodic pattern of repetition. Therefore, noise is regarded as a mixture of sound waves with irregular frequencies. • Music,on the other hand, is a pleasant sound that has a clear pitch. Musical sound can be created by arranging and combining different sounds in a particular order. The frequencies of a musical sound are harmonious in nature.
- 19. NOISE POLLUTION • Noise pollution can be defined as the presence of undesirable and unpleasant sounds in the earth's environment. • Human beings can bear sounds ranging up to 85 decibels only. Above that, any noise can damage our hearing power. • Generally, any sound that has a frequency of more than 30 dB is considered noise.
- 20. • The unwanted noise causes an adverse effect on the health of the organisms present on the earth. • According to the World Health Organization, the maximum sound limit that is ideal for cities is 45 dB only. • However, it has been found that the sound range in many big cities of the world lies up to 90 dB. • Hence noise pollution is common in many cities today and even rural areas to a great extent.
- 21. CAUSES OF NOISE POLLUTION • Construction Noise • Neighbourhood Noise • Industrial Noise • Natural Sounds • Transport Noise • Bursting of Fireworks
- 22. EFFECTS OF NOISE POLLUTION • Excessive noise in the surroundings can lead to serious health problems such as hypertension, lack of sleep or insomnia, anxiety, lack of memory, stress, irritation and even nervous breakdown. • It can lead to temporary or permanent hearing loss in human beings as well as animals. • Excessive noise leads to increased blood pressure. It increases cholesterol levels in the blood and therefore increases the chances of cardiovascular diseases in a person. • If sound intensity is more than 180 dB it can lead to the death of a person.
- 23. PREVENTION OF NOISE POLLUTION • Factories and other industries should be set up at a distance from residential areas. • Silencing devices should be incorporated into heavy vehicles such as aircraft, industrial equipment, machinery and other home appliances. • Use of horns should be minimized especially near public places such as hospitals, religious places and schools.
- 24. • Trees should be planted in huge numbers as they can absorb unwanted noise from the environment. • People who work in noisy conditions such as industries and mines should be provided earplugs to protect their ears.
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