Sound Energy PDF

## 8.4 Sound Energy ### What is sound? 1. Sound is a form of energy that can be heard and travels in waves. 2. When matter vibrates or moves back and forth very quickly, a sound is made. 3. Sound waves can travel through solids, liquids, or gases. 4. For example, when a school bell rings, part of...

## 8.4 Sound Energy ### What is sound? 1. Sound is a form of energy that can be heard and travels in waves. 2. When matter vibrates or moves back and forth very quickly, a sound is made. 3. Sound waves can travel through solids, liquids, or gases. 4. For example, when a school bell rings, part of the bell will vibrate creating a sound. ### Properties of Sound 1. A sound is made when things vibrate. 2. Sound travels in waves. 3. Sound is a longitudinal wave. 4. Sound must travel through matter to be heard. 5. The vibrating object makes the air around it vibrate. 6. Sound vibrations move through the air into your ears and make the eardrums vibrate. 7. Denser the medium, the faster sound travels. 8. Volume is how loud or soft a sound is. 9. Pitch is how high or low a sound is. _A diagram of a vibrating object, the movement of air particles and resulting sound waves is shown._ ### How does sound reach your ear? And how does your ear function to capture the sound? 1. Sound waves are sent. 2. The outer ear "catches the sound waves". 3. The middle ear takes the sound waves and "vibrates" the eardrum. 4. The inner ear sends the messages to the brain. 5. The brain puts it together and... hooray! You hear your favorite song on the radio. _A diagram of a wave is shown_. ### Speed of Sound 1. The speed of sound depends on the medium through which it is moving. 2. The speed doesn't depend on how loud or soft the volume is. Or how low or high the pitch is. 3. All sounds travel through a certain kind of medium at the same speed. 4. If the medium changes, the speed of the sound changes. 5. Sound moves faster in warm air than in cold air. _For example, when a drum stick is struck, it vibrates causing the air beside the drum to vibrate. The compression and stretching of air particles creates a sound wave which is carried through the air to your ear._ ### How does sound travel? 1. Sound travels in waves that move in all directions from the object that makes the sound. 2. Sound must travel through matter to be heard. The matter can be a solid, a liquid, or a gas. 3. When the sound hits something, some or all of the energy is absorbed. 4. Soft surfaces absorb more sound energy than hard surfaces. 5. A sound that hits a hard surface bounces back (not much of it is absorbed). 6. An 'echo' is a sound that bounces off of a surface. 7. Sound passes through the medium as longitudinal waves. 8. When the vibrations are fast, you hear a high pitch. 9. When they're slow, you hear a low pitch. ### Movement of Sound waves 1. Sound energy waves move like the domino effect". 2. Sound waves can carry energy a long distance. 3. The energy travels from place to place, but the matter that carries the energy stays where it is. 4. Remember: air is not the only matter that can carry sound waves. 5. Any kind of matter can be made to vibrate and carry sound. 6. Medium is the matter that carries sound waves. ### Sound Travels Through Matter - **Gases:** Most of the sounds we hear travel through gases, such as air. For example: Sound from a bell, a horn, or an alarm clock travels through the air. - **Liquids:** Some sounds that we hear travel through water. Sonar is the way to use sounds to locate objects underwater. - **Solids:** Some sounds that we hear travel through solids. For example, When you hit a drum, it vibrates, then the sound travels through the air, to your ears. **In which state of matter - solids, liquid or gases, does sound travel the best?** - Sound travels fastest and is heard the best through solids. - Sound travels the slowest and is the quietest when travelling through gases. - Sound travels at different speeds in different states of matter/materials. **Can sound travel in a vacuum? Explain** For sound to be heard, sound vibration must have air or some other kind of matter or medium to travel through. _In space, where there is no air, sound has no way to travel. You cannot hear sound in outer space because there is no air or other matter to carry sound vibrations. Thus, sound cannot travel in a vacuum. No, you cannot hear any sounds space._ **How do you think astronauts are able to talk to each other in outer space?** ### Sound waves are longitudinal waves A sound wave is the pattern of disturbance caused by the energy travelling away from the source of the sound. Sound waves are longitudinal waves. This means that the propagation of vibration of particles is parallel to the energy wave propagation direction. When the atoms are set in vibration they move back and forth. This continuous back and forth motion results in a high-pressure and a low-pressure region in the medium. These high-pressure and low-pressure regions are termed compressions and rarefactions, respectively. These regions are transported to the surrounding medium resulting in the sound waves travelling from one medium to another. _A diagram of sound waves is shown, including compression, rarefaction, amplitude, wavelength, and oscillation._ ### Terms related to sound waves - **Oscillation:** The to and fro motion when full wave is constituted is known as one oscillation. A wave starting from Preaching Q denotes one oscillation. - **Wavelength (λ):** The length of a wave along the X axis is wavelength. Sl unit – metre - **Frequency (f):** The number of oscillation made by a wave in a unit time is called its frequency. Sl unit – hertz (Hz) - **Time period (T):** The time taken by the wave to complete one oscillation is called its time period. Sl unit of T is second(s). - **Amplitude (A):** The maximum displacement of a wave on either side of its mean position is called its amplitude. Sl unit - metre. ### Nature of Sound The sound produced by a guitar is different from the sound produced by a drum. This is because the sound produced by different sources have different characteristics. Sound can be characterized by its frequency, wavelength, and amplitude. #### Frequency of sound The number of rarefactions and compressions that occur per unit time is known as the frequency of a sound wave. The formula of the frequency of a wave is given as: $f = \frac{1}{T}$ Where, - f - frequency, - T - time period #### Wave Length of wave (λ) The distance between the successive compression and rarefaction is known as the wavelength of a sound wave. ### Characteristics of Sound - **A: Pitch** 1. It is characteristic of sound which determines the shrillness of a sound. 2. It describes how shrill or bass a sound is. 3. It depends up on the frequency of vibration. 4. Objects that vibrate slowly, make a low pitch. Example: Drums. 5. Objects that vibrate quickly, make a higher pitch. Example: Recorder - **B- Loudness or Volume** 1. Volume is the loudness or the softness of a sound. 2. Loud sounds use a lot of energy. 3. Soft sounds use a little energy. 4. Loudness of a sound depends on intensity, the amplitude of a wave. 5. If amplitude is less, the sound is feeble. 6. Higher the amplitude, louder the sound. 7. Measured in decibels (dB)-- talking is 50db, and sounds over 120dB are painful. 8. Example: The harder a drum is hit, the more the drum will vibrate. The more an object vibrates, the louder the sound it makes. **How else can we change sound?** We can make it louder or softer by changing the amplitude of the height of the wave. The higher the amplitude, the louder the sound. The lower the amplitude the softer the sound. **How do humans make Sounds?** We use our vocal cords to make sounds in our throat. When we speak, our vocal cords vibrate. Place your hand on your throat when you talk, and you can feel the vocal cords vibrate. **Why are some sounds louder than others?** 1. The source of the louder sound is vibrating more. 2. These sound waves have more energy. 3. A sound's loudness can be measured in units called decibels. - **Pitch** 1. It depends on frequency. 2. It that characteristic of a sound by which a shrill sound can be distinguished from a grave or a flat sound. 3. It does not depend upon the sound energy received by the ears. - **Loudness** 1. It depends on amplitude. 2. It is that property of a sound by virtue of which a loud sound can be distinguished from a faint one. 3. It depends on the amount of sound energy received by the ears per unit time. - **C. Quality or timbre** Quality is that characteristic of sound which helps us to distinguish between two sounds having the same pitch and loudness. ### Pitch and Volume of Sound - **_Pitch_** depends on the frequency of the sound waves. - **_Intensity_** depends on the amplitude of the sound waves. - **_Volume_** is the loudness or the softness of a sound. It is measured in (dB). - **_Pitch_** determines the shrillness of a sound. It depends upon frequency. _A diagram of a crow, koyal, a group of birds , and a lion is shown. Below each is an image of a sound wave showing low vs high pitch, and high vs low intensity._ _When vibrations are slow, we get low frequency notes, and the sound is low. When vibrations are fast, we get high frequency, and the sound is loud._ ### Characteristics of sound 1. The sound produced by one person is different from that of another. 2. This is because every sound has different characteristic properties such as loudness, pitch and quality. 3. Loudness depends upon: a) Amplitude: Vibrations of large amplitude produce loud sounds and vice-versa. Loudness ∞ (amplitude)² b) Distance between the listener and the source: as distance increases, the loudness decreases. c) Area of vibrating body: Larger the area, larger is the sound produced. 4. Sensitivity of the ear to the sound. 5. Loudness of sound does not depend upon the frequency of the vibrating particle. _A diagram illustrating amplitude, frequency, and loudness is shown._ ### Reflection of sound _Have you noticed that your voice sounds louder, when you sing in a bathroom, than when you sing in a larger room?_ _This is because sound gets reflected from the walls of a small room and rebounds many time._ - The bouncing back of sound on striking a surface is called reflection of sound. - All materials do no reflect sound equally. - Hard surfaces are good reflectors of sound, whereas soft and fluffy objects are bad reflectors of sound. - This property is used in acoustics of buildings. The walls, ceilings and floors of auditorium and cinema halls are covered with absorbing materials to prevent transfer the sound to extemal surrounding. _A diagram of sound waves reflecting off a wall in a room is shown._ #### Application of reflection of sound. - **Echo:** is the sound that is heard by an observer after it is reflected from a rigid surface. - Human ear can hear two sounds separately if there is an interval of (1/10)th of a second. Therefore, for two sounds to be clearly heard, there must be minimum time interval of 1/10th of a second. - The total distance travelled by sound from the source to the surface and back to the source from the surface would be 2d. - The speed of sound in air is 340 m/s. - Total distance = speed x time - 2d = 340 x 1/10 - 2d = 34 - d = 17 m _A diagram of a person standing a distance, d, from a wall and the sound wave reflecting off the wall is shown._ - The reflecting surface should be at least 17 m away from the source to hear an echo. - For an echo to be heard, 1. The size of reflector should be large. E.g a mountain 2. The original sound should be of a very short duration so that echo does not mix with the original sound. #### Wave equation: speed = frequency x wavelength v = f x λ ### Sonar **Sonar- Sound Navigation And Ranging.** 1. It is a device used for following purposes: 2. Measures depth of the sea 3. To locate under water objects like shipwrecks, submarines, sea rocks 4. Sonar sends out ultrasonic waves towards the bottom of the sea. The reflected sound waves (echo) from sea bed is received and time for the sound to reflect back is noted. _Two diagrams of boats are shown, sending and receiving sound waves out to measure the depth of the ocean._ ### Audible and Inaudible sound _The human ear can hear sound wave with frequencies between 20Hz and 20kHz._ - Sound waves with frequencies less than 20Hz are called infrasonic or subsonic. - Sound waves with frequencies above 20kHz are called ultrasonic. _A diagram showing, below 20 Hz, infrasonic; 20Hz to 20,000Hz, audible sound; and over 20,000Hz, ultrasonic is shown. A diagram of an elephant, a person, and a bat is shown under each of the frequency ranges._ ### Uses of ultra sonic sound - Bats, whales, seals can produce ultrasonic sound. These sound wave return to them after getting reflected from the object. This helps them to detect prey or obstacles in their path. - They are also used for imaging and scanning internal organs of the body. Reflected waves from the different portions of the organ are used to create a picture of the organ. It is used in sonar. - They are also used to detect fine faults in metals sheets for use in aviation, spaceships and machinery. - They are used by fishermen to locate a shoal of fish in the sea. - They are used for removal of grease or dirt from materials and tartar from teeth. _A diagram of a person being imaged during a sonogram, a whale, and a person cleaning their teeth using an electronic toothbrush is shown._ ### Decibel scale 1. The loudness or intensity of a sound is measured on a special scale called decibel scale. 2. Bell is the unit of loudness. 3. Decibel is the smaller unit of loudness. 4. 1 decibel is equal to one tenth of a bell. 5. The minimum audible sound is considered to be at the 0 decibel level. 6. The loudest sound that can be tolerated by the human ear is about 140 dB. 7. Sounds of intensity more than 140 dB produce pain in the ears and can damage the delicate tissues inside the ears. ### Noise pollution The disturbing or excessive noise may harm or drastically affect the balance of human or animal life, the cause of such situation leads to noise pollution. - The loudness of sound is considered normal if it is between 50 dB to 60 dB. - Any sound above 80 dB causes noise pollution. ### Harmful effects of noise pollution - Permanent hearing loss in humans as well as in animals. - Noise reduces concentration. - Excessive noise may interfere with the sleeping patterns. - It may cause headache, tension, high blood pressure even anger. - Infant kids and elderly people are at a higher risk of developing hearing impairment due to noise. ### Measures to control noise pollution - Use of loud speakers should be restricted. - Factories should not be located in residential areas. - Entry of heavy vehicles in residential areas should be restricted, etc. - Televisions and music systems should be played at appropriate sound levels. - Factory workers must use ear plugs to save themselves from loud noise. - Rooms, halls and indoor stadiums should be sound insulated in order to prevent transfer of noise to surroundings _A diagram shows a person standing next to a loud, noisy pollution sign. Next to them are four people with annoyed expressions._ _A table with the following noise levels and their sources is shown._ - Gunshot, Metal concert - 130 - Jet Plane take off - 120 - Industrial noise - 110 - Subway train - 100 - Bass drum - 90 - Loud radio - 80 - Hairdryer, Noisy restaurant - 70 - Busy street, Alarm clock - 60 - Conversation - 50 - Moderate snoring - 40 - Whisper, Light snoring - 30 - Quiet room - 20 - Breathing - 10 - Threshold of human hearing - 0