Properties of Sound

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  • Whenever an object in air vibrates, it causes longitudinal or compression waves in the air. These waves move away from the object as sound. There are many forms of the vibration, some not so obvious. The back and forth movement of a loudspeaker cone, guitar string or drum head result in compression waves of sound. When you speak, your vocal cords also vibrate, creating sound. Blowing across a bottle top can also create sound. In this case, the air inside the bottle goes in a circular motion, resulting in sound waves being formed. Wind blowing through trees can also create sound this indirect way. Sound can also be created by vibrating an object in a liquid such as water or in a solid such as iron. A train rolling on a steel railroad track will create a sound wave that travels through the tracks. They will then vibrate, creating sound in air that you can hear, while the train may be a great distance away.
  • Demo: have one student stand and count out loud how many "wave" pass by. Have 3 students stand close together in a line and pass by the "counter" very slowly to generate a frequency of 3Hz. Have another group of 3 students stand arms-length apart and pass by the "counter" quickly to also generate a frequency of 3Hz. Explain that both of these waves would generate the same pitch because they have the same frequency. However, the two waves would have to be traveling in different mediums in order for this to happen.
  • The outer ear consists of the pinna, which is the external skin and cartilage on both sides of our heads that we think of when we hear the word “ear,” as well as the external auditory canal. The shape of the pinna is ideal to collect the sound waves, direct them down the ear canal, and vibrate the tympanic membrane, or eardrum. The eardrum separates the outer ear from the middle ear. In the middle ear, the eardrum’s vibrations move the Malleus (hammer), the Incus (anvil) and the Stapes (stirrup) bones of the middle ear, collectively known as the ossicles. With motion of the ossicles, the sound waves that first entered the ear canal have been converted to mechanical energy, and this energy is conducted toward the inner ear. Movement of the ossicles causes vibrations in the fluid of the cochlea, the hearing portion of the inner ear. As the cochlear fluid vibrates, it moves thousands of tiny hair-like nerve cells that line the cochlear walls, which serves to convert the mechanical energy of the ossicles into the requisite electrical nerve impulses. These impulses travel from the cochlea up the auditory nerve, where they are received and given meaning and relevance by the brain. The cone-shaped bone that forms the part of the skull immediately below and behind each ear is called the mastoid process. The internal ear structures and hearing processes are protected deep within this bone.
  • The outer ear consists of the pinna, which is the external skin and cartilage on both sides of our heads that we think of when we hear the word “ear,” as well as the external auditory canal. The shape of the pinna is ideal to collect the sound waves, direct them down the ear canal, and vibrate the tympanic membrane, or eardrum. The eardrum separates the outer ear from the middle ear. In the middle ear, the eardrum’s vibrations move the Malleus (hammer), the Incus (anvil) and the Stapes (stirrup) bones of the middle ear, collectively known as the ossicles. With motion of the ossicles, the sound waves that first entered the ear canal have been converted to mechanical energy, and this energy is conducted toward the inner ear. Movement of the ossicles causes vibrations in the fluid of the cochlea, the hearing portion of the inner ear. As the cochlear fluid vibrates, it moves thousands of tiny hair-like nerve cells that line the cochlear walls, which serves to convert the mechanical energy of the ossicles into the requisite electrical nerve impulses. These impulses travel from the cochlea up the auditory nerve, where they are received and given meaning and relevance by the brain. The cone-shaped bone that forms the part of the skull immediately below and behind each ear is called the mastoid process. The internal ear structures and hearing processes are protected deep within this bone.
  • baby at 20 weeks, echocardiogram of human heart
  • Bats, dolphins, dogs, fish & insects all hear ultrasonic frequencies. Another well-known application of this same basic technique is sonar . In sonar, ultrasonic waves are emitted, and sensors detect the reflected portions of those waves. The sensors end up creating an image of any obstruction in their path, much like the image shown in Figure 14.6. Although sonar is best known as the way a submarine tracks ships and other submarines, the most efficient sonar known to humankind exists in the bat.
  • We have seen that the echo of a sound can be used to determine how far away something is, and we have also seen that we can use the Doppler shift of the echo to determine how fast something is going. It is therefore possible to create a "sound radar," and that is exactly what sonar is. Submarines and boats use sonar all the time. You could use the same principles with sound in the air, but sound in the air has a couple of problems: Sound doesn't travel very far -- maybe a mile at the most. Almost everyone can hear sounds, so a "sound radar" would definitely disturb the neighbors (you can eliminate most of this problem by using ultrasound instead of audible sound). Because the echo of the sound would be very faint, it is likely that it would be hard to detect. Radar therefore uses radio waves instead of sound. Radio waves travel far, are invisible to humans and are easy to detect even when they are faint.
  • Properties of Sound

    1. 1. Properties of Sound Powerpoint Templates
    2. 2. • Incredible Human Machine video – how sounds are perceived & produced (5:35) Powerpoint Templates
    3. 3. What is Sound?• A sound is any vibration (wave) traveling through the air or other medium which can be heard when it reaches a persons ear. • Sounds waves are: • Longitudinal - oscillations parallel to propagation • Mechanical - require a medium to travel through Powerpoint Templates
    4. 4. How Sound is Created• When an object vibrates, it creates sound – loud, deep and long, short and high-pitched – pure, gravely, distorted, sweet, soft, piercing, buzz• Any sound your ear can hear is created by the mechanical back-and-forth motion of an object Powerpoint Templates
    5. 5. Powerpoint Templates
    6. 6. Amplitude & Volume• The amplitude of a wave determines a sounds volume. – Volume tells how loud or soft a sound is • determined by how much energy a wave carries. – Amplitude describes how much energy a wave is carrying: • more energy = greater amplitude = louder sound • greater amplitude = taller wave or more intense compressionsHigher Amplitude Loud Lower Amplitude QuietHigher Amplitude Lower Amplitude Loud Quiet Powerpoint Templates
    7. 7. Decibels & Sound Volume • Audible sound energy is measured in decibels (dB) – Only measures within the limits of human hearing • 0 is just barely audible • 120+ causes pain/damage – figured by powers of 10 • 20 dB is 10 x 10 times > 0dB (100 times great than 0 dB) • 30 dB is 10 x 10 x 10 greater (1,000 times > 0 dB) • Hearing damage depends on: – sound amplitude (loudness) – frequency (pitch) of the sound – duration of exposure to the sound Powerpoint Templates
    8. 8. Frequency & Pitch• Pitch tells how high or low a sound is – a higher pitch will have greater frequency (more waves crammed into each second of time) • higher frequencies have smaller wavelengths Sample tones Rubens Tube video Sand Vibration Patterns • Nodes = areas of zero displacement – sand is not moved – flame is not shot out of holes Powerpoint Templates
    9. 9. Wavelength & Pitch• Two things affect frequency: Student Demo – wavelength and wave speed • slow moving wave pattern and small wavelength • quickly moving wave pattern and large wavelength• Sound waves will move at a constant speed unless: – they are moving through different mediums – they are moving in mediums of different temperatures – the source creating the sound is moving (train, ambulance, etc.)It is usually a change in wavelength that results in a different pitch. Powerpoint Templates
    10. 10. More about Frequency• Sound waves can be absorbed by objects. – Higher frequencies (smaller wavelengths) are absorbed more than lower frequencies (bigger wavelengths). Powerpoint Templates
    11. 11. How Sound is Heard• Sound waves are funneled by the pinna into the ear canal.• The tympanic membrane is then vibrated like a drum by the compressional sound waves.• Tiny bones (ossicles) transfer the wave motion to a soft, fluid-filled organ in the inner ear. Powerpoint Templates
    12. 12. The Inner Ear• The spiral-shaped cochlea has tiny, hair-shaped cells inside that transfer the mechanical energy (back-and-forth motion) of the wave into electrical energy (nerve impulses). • Your brain interprets different tone pitches depending on which cells in the cochlea are moved by the sound wave passing through the fluid. – high frequencies stimulate the base – lower pitches make the hairs of the apex (center) vibrate hair cells Powerpoint Templates
    13. 13. Ears and Balance• As your body moves, hair cells in the semicircular canals are bent over when the fluid inside flows past them.• Three canals oriented in 3 directional planes: – yaw (rotation), pitch (forward/back), and roll (side to side) Powerpoint•Templates Not affected by sound waves.
    14. 14. Limits of Human HearingFrequencies ABOVE what humans can hear are ultrasonic waves (20,000+ Hz).Frequencies BELOW what humans can hear are infrasonic waves (0 to 20 Hz). Powerpoint Templates
    15. 15. Speed of Sound Medium Speed (m/s) Gases • Density and temperature Air (20°C) 343 affect how fast sound will Air (0°C) 331 travel through a medium Liquids at 25°C – Sound travels fastest in solids, Sea water 1533 then liquids and more slowly Water 1493 in gases Mercury 1450 – Sound travels faster in warmerMethyl alcohol 1143 air than cold air Solids Rubber 1600 Gold 3240 Iron 5130Pyrex glass 5640 Diamond 12000 Powerpoint Templates
    16. 16. Calculating Distance with Sound• Light travels at almost 300,000,000 meters per second• Speed only moves at roughly 340 m/s – This is why you always SEE lightning before you HEAR it!• What is the formula for speed? Speed = distance/time (s=d/t)• To figure the distance of a storm: speed x time – There are 1,609 meters in a mile. (~340 x 5) – So for every 5 seconds we count, the storm is 1 mile away. Thunderstorm Calculator Powerpoint Templates
    17. 17. Ultrasound • Ultrasound is a wave frequency higher than is detectable by the human ear. • A probe transmits millions of sound pulses into the body each second. • Some waves are reflected as they travel through boundaries between tissues (i.e. fluid & soft tissue, soft tissue & bone). • Reflected waves are picked up by the probe and relayed to the machine. • A computer calculates the distance from the probe to each tissue boundary using the speed of sound and the time of each echos return. (speed = d/t)• The distance and intensity of each echo is then displayed as a screen image.• Used to "see" inside and diagnose many different body areas. Powerpoint Templates
    18. 18. Other Uses of Ultrasound• Veterinary Medicine• Cleaning & Disinfection• Humidifiers• Welding• Pest Control• Animal Navigation & Communication• SONAR• Sonic Weapons Powerpoint Templates
    19. 19. The Doppler Effect• As a motorcycle speeds forward, the frequency (pitch) of the sound waves in front of the motorcycle become higher, and the frequency (pitch) of the sound waves behind it become lower.• As the object making the sound moves, the waves get bunched up.• "Bunched up" waves have a smaller wave- length, thus a higher frequency (pitch). wavelength Powerpoint Templates
    20. 20. Moving Sound Source A stationary sound source. Sound waves are produced at a constant frequency, and the wavefronts move symmetrically away from the source at a constant speed. All observers will hear the same frequency, which will be equal to the actual frequency of the source. The same source is creating sound waves at the same frequency. However, the source is moving to the right, so the center of each new wavefront is slightly displaced. As a result, the wavefronts begin to bunch up on the right side (in front of) and spread further apart on the left side (behind) of the source. An observer in front of the source will hear a higher frequency, and an observer behind the source will hear a lower frequency (pitch). Powerpoint Templates
    21. 21. Doppler RadarHow it works:• Radar gun sends out waves• Waves bounce off moving objects and return to radar gun• If the object is moving when the wave is reflected, the frequency of the wave will be changed - the Doppler effect• The guns sensor records the change in frequency and uses that to calculate the objects speed. Powerpoint Templates
    22. 22. Sonic Booms• Science is Fun video• When an object moves FASTER than the speed of sound, it punches through all the bunched up waves in front of it, creating an audible sound – a sonic boom is made the instant all the bunched wave fronts join to make one very loud (high amplitude) longitudinal sound wave • Mach 1 = the speed of sound – named after Austrian physicist and philosopher Ernst Mach • Faster-than-sound velocities are called supersonic speeds Powerpoint Templates

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