Cc20 p   topic 5.3 sound
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Cc20 p   topic 5.3 sound Cc20 p topic 5.3 sound Presentation Transcript

  • CC20P Copyright – Pinnacle Learning Center Key Objectives Topic 5.3 Sound • Describing the production of sounds • Measuring the speed of sound • Relating pitch and loudness to frequency and amplitude • Describing how sound travels • Describing the production of sounds • Measuring the speed of sound • Relating pitch and loudness to frequency and amplitude • Describing how sound travels
  • CC20P Copyright – Pinnacle Learning Center 1. Introduction 2. Sound Waves 3. Speed of Sound 4. Reflections of Sound 5. Viewing of Sound 6. Sound Intensity and Noise 7. Hearing Range 8. Infrasound 9. Ultrasound Topic Summary
  • CC20P Copyright – Pinnacle Learning Center Introduction View slide
  • CC20P Copyright – Pinnacle Learning Center Making Sounds We all make sounds.... • We speak • Play the violin • Knock on the door.... • We put the radio on In all of these, some parts vibrate, and this causes the air nearby to vibrate. Sound travel through air to our ears as vibrations. View slide
  • CC20P Copyright – Pinnacle Learning Center Making Sounds • So what is Sound? Sound are actually waves!
  • CC20P Copyright – Pinnacle Learning Center Sound • Sound is a form of energy, produced whenever an object vibrates (a guitar string / vocal cords / loudspeaker etc…) • Sound travels as a wave, similar to light, but for sound to travel it needs to vibrate particles. • Sound cannot travel through a vacuum (no particles to vibrate) - in space, no-one can hear you scream!
  • CC20P Copyright – Pinnacle Learning Center Sound • Sound travels by vibrating one particle, which vibrates it neighbours, which vibrate theirs etc… Vibration in same direction as wave is traveling Wave traveling
  • CC20P Copyright – Pinnacle Learning Center Sound Waves
  • CC20P Copyright – Pinnacle Learning Center Sound Waves • Sound waves are longitudinal waves produced by a vibrating source, which causes material to vibrate. • A material or medium is required to transmit sound waves, and the medium moves in the same direction of the wave. • Sound waves can travel through: – Air – Liquid – Solids Sounds cannot travel through a vacuum!
  • CC20P Copyright – Pinnacle Learning Center Sound Waves • As sound travels through a material, ‘compressions’ and ‘rarefractions’ occur. Rarefraction Compression Rarefraction − Compressions are regions where particles of material are close together. − Rarefractions are regions of material where the particles move further apart.
  • CC20P Copyright – Pinnacle Learning Center Sound Waves • The compressions and rarefactions of the air particles is shown below: • The air particles move from left to right, in the same direction of the wave Rarefraction Compression Compression Rarefraction Compression Rarefraction Compression Wave direction
  • CC20P Copyright – Pinnacle Learning Center Speed of Sound
  • CC20P Copyright – Pinnacle Learning Center Speed of Sound • Sound travels at different speeds through different substances, traveling at 330 m/s through air (light travels at 300,000 km/sec or 300,000,000 m/s)! • Watch a firework display / thunder and lighting during a storm, and you always see the light before you hear the noise • Sound travels as a wave, but it needs to vibrate particles to travel
  • CC20P Copyright – Pinnacle Learning Center Calculating Speed of Sound • If you know the distance a sound wave has travelled, and you know the time taken, you can calculate the speed. Speed, v = Distance, D Time, t
  • CC20P Copyright – Pinnacle Learning Center Different Materials, Different Speeds • At 0o C, speed of sound in air is 330 m/s • The speed of sound actually changes with the air temperature. • Sound also travels faster through solids than through gases. • And in liquids, the speed is in between that in solids and gases.
  • CC20P Copyright – Pinnacle Learning Center Sound & Matter • Sound needs a substance to travel through and travels by particles vibrating - which state of matter does sound travel fastest through? GasSolid Liquid Sound waves travel fastest through solids - the particles in a solid are closer together than in a gas or a liquid meaning vibrations are more easily passed from particle to particle and so sound travels faster
  • CC20P Copyright – Pinnacle Learning Center Speed of Sound in Different Materials • Sound waves disperse less energy when moving through a medium of greater density • In other words, the denser the medium the faster the sound passes through it (generally) Sound travels through the iron much more quickly than through air, as the iron is so much more dense (particles are much closer together)
  • CC20P Copyright – Pinnacle Learning Center Speed of Sound in Different Materials Material Speed of Sound (m/s) Gases Air 330 Hydrogen 1280 Oxygen 316 Liquids Water 1500 Sea water 1530 Mercury 1450 Solids Glass 5000 Iron, steel 5100 Lead 1200 Wood (oak) 3800 Measured at standard temperature and pressure
  • CC20P Copyright – Pinnacle Learning Center Sound in Vacuum There is air inside the bell jar so the sound can travel and be heard Vacuum pump on Remove the air from the bell jar and the sound cannot be heard because there are no air particles to vibrate
  • CC20P Copyright – Pinnacle Learning Center Reflection of Sound
  • CC20P Copyright – Pinnacle Learning Center What are echoes? • Sound can reflect from the surface of an object - this is called an echo Which surfaces reflect sound better? • Hard surfaces reflect sound better than soft surfaces – which is one reason why classrooms without carpets or curtains can be noisy places
  • CC20P Copyright – Pinnacle Learning Center Why do you hear echoes in caves? • Hard surfaces reflect sound better than soft surfaces • Sound is reflected well by large solid objects, so in caves the sound is reflected well from the solid cave wall  Why do echoes usually sound quieter?  As the sound wave travels some energy is lost, so you usually hear your echo with less amplitude (volume)
  • CC20P Copyright – Pinnacle Learning Center • You can work out how far away something is using the reflection of waves • If you stood at the entrance of a cave and shouted, how could you work out how far away the back of the cave was? Distance = Speed x Time • If the echo took 20 seconds to be heard after you shouted, how far back is the cave? Distance = 330m/s x 20 seconds Distance = 6,600m • However, the distance is from your mouth, to the back of the cave, and back again! So we need to halve this result – distance to back of cave is therefore 3,300 m
  • CC20P Copyright – Pinnacle Learning Center • Sonar stands for sound navigation and ranging – a technique used to measure how far away something is • The boat sends out a sound wave which hits the sea bed • The sound wave reflects off the surface, back to the receiver – the time it takes can be used to calculate the distance
  • CC20P Copyright – Pinnacle Learning Center • Sound travels at 1480m/s through water • If the sound took 0.3 seconds to get back to the boat, what is the distance? Distance = Speed x Time Distance = 1480m/s x 0.3 seconds Distance = 444m However, this is the sound travelling there and back, so we need to ÷ 2 Distance = 222m Sound travels at 1480m/s through water - if the sound took 0.3 seconds to get back to the boat, what is the distance?
  • CC20P Copyright – Pinnacle Learning Center • Sonar is used by bats to help them navigate • They send out very high pitched sounds, and detect the echoes – the quicker the echo comes back, the nearer the object is • Bats are so good at this, they are able to fly in total darkness (useful when living in a cave)!
  • CC20P Copyright – Pinnacle Learning Center Viewing Sound
  • CC20P Copyright – Pinnacle Learning Center Viewing Sounds Huh? How do we view sounds? • We can depict sounds on an oscilloscope
  • CC20P Copyright – Pinnacle Learning Center Viewing Sound • Sound can be studies using a signal generator to produce different types of sound, a loudspeaker so we can hear the sound, and a oscilloscope which lets us ‘see’ the sound Signal generator (produces different sounds) Loudspeaker (allows us to hear the sound) Oscilloscope (turns the sound into a visual signal)
  • CC20P Copyright – Pinnacle Learning Center Viewing Sounds • The sound is ‘captured’ by a microphone connected to an oscilloscope. • The microphone receives the sound vibrations and converts them to an electrical signal, which is displaced on the oscilloscope screen. • The trace on the screen shows the regular up-and-down pattern of the vibrations that make up the sound.
  • CC20P Copyright – Pinnacle Learning Center Sound Waves • Listen to the different sounds produced as the frequency changes – listen carefully to where your hearing begins / ends • As you listen, view the oscilloscope to see how the waves are changing
  • CC20P Copyright – Pinnacle Learning Center Amplitude • A sound can be quiet or loud • Amplitude is a measure of how loud a sound is (how much energy the wave carries) – a big amplitude means a loud sound A quiet sound on an oscilloscope (short wave height) A loud sound on an oscilloscope (tall wave height)
  • CC20P Copyright – Pinnacle Learning Center Amplitude • Which trace represents the greatest amplitude (loudest sound)? Sound A has the largest amplitude (tallest waves) so is the louder of the two sounds Sound A has the largest amplitude (tallest waves) so is the louder of the two sounds A B
  • CC20P Copyright – Pinnacle Learning Center Pitch & Wavelength • A sound can be low (mooing cow) or high (squeaking mouse) • Pitch depends on the frequency of the waves (number of complete vibrations each second, measured in hertz (Hz)) A low pitch sound on an oscilloscope (few wave per second) * long wavelength A high pitch sound on an oscilloscope (many waves per second) * short wavelength
  • CC20P Copyright – Pinnacle Learning Center Pitch & Wavelength • Which trace represents the highest pitch, like that of a squeaking mouse (shortest wavelength)? Sound B has the most waves across it (short wavelength for each wave) meaning it has a higher frequency = higher pitch Sound B has the most waves across it (short wavelength for each wave) meaning it has a higher frequency = higher pitch BA
  • CC20P Copyright – Pinnacle Learning Center Wave Variations
  • CC20P Copyright – Pinnacle Learning Center Wave Envelopes • Sounds can vary greatly in their amplitude (loudness) and frequency (pitch) • Listen and visualise the sounds and their wave envelopes
  • CC20P Copyright – Pinnacle Learning Center Sound Intensity & Noise
  • CC20P Copyright – Pinnacle Learning Center Sound Intensity
  • CC20P Copyright – Pinnacle Learning Center Sound Intensity 160 140 120 100 80 60 40 20 0 permanent ear damage can just be heard aircraft overhead decibels circular saw at 2m quiet countryside pin being dropped loud bell personal stereo
  • CC20P Copyright – Pinnacle Learning Center Noise
  • CC20P Copyright – Pinnacle Learning Center Hearing Range
  • CC20P Copyright – Pinnacle Learning Center Hearing Range • We hear a range of sounds from low pitch to high pitch – this is the audible range. • The normal range of hearing in humans is 20 Hz to 20,000 Hz, but the upper limit decreases with age. • Poor hearing can be due to wax blocking ears, nerve damage, infections. • Some animals can hear much better than humans – e.g. Dogs (up to 40,000 Hz!), bats and dolphins can hear much higher frequencies than humans
  • CC20P Copyright – Pinnacle Learning Center Hearing Range The frequency range audible to humans is from 20Hz to 20,000Hz. Below 20Hz are infrasounds, above 20,000 are ultrasounds.
  • CC20P Copyright – Pinnacle Learning Center Hearing Range
  • CC20P Copyright – Pinnacle Learning Center Infrasound D. Crowley, 2008
  • CC20P Copyright – Pinnacle Learning Center Infrasound Infrasound is a sound that is below the range of human hearing (i.e. below 20 Hz). Some animals use infrasound to communicate.
  • CC20P Copyright – Pinnacle Learning Center Infrasound is also produced by volcanoes and earthquakes. Some people believe that animals can sense these infrasounds before the eruptions or earthquakes start. Infrasound
  • CC20P Copyright – Pinnacle Learning Center Vladimir Gavreau was an infrasound pioneer. While conducting experiments in the 1950s he became aware that his lab assistants were experiencing pain due to low frequency sounds. He used this information to produce and infrasound gun. This was lethal as it rapidly induced internal bleeding when used on humans. At low power it would shake walls and ceilings to pieces. Whales, alligators, elephants and rhinos all communicate by infrasound. Infrasound
  • CC20P Copyright – Pinnacle Learning Center Ultrasound D. Crowley, 2008
  • CC20P Copyright – Pinnacle Learning Center Ultrasound • Ultrasound is sound with a higher frequency than we can hear (i.e. above 20,000 hertz) • In nature some organisms, including bats, utilise ultrasound (they produce very high pitched squeaks, and convert the echoes into a picture of their surroundings, which is why they can fly at night) Although we cannot hear ultrasounds, we can use them for a variety of things…
  • CC20P Copyright – Pinnacle Learning Center Ultrasound Uses - Industrial Cleaning • Ultrasound can clean delicate machines without the need to dismantle them • Ultrasounds can be directed to very precise areas and be uses to vibrate dirt away – this is also used for cleaning teeth (ultrasounds can remove tartar (this can lead to gum disease)
  • CC20P Copyright – Pinnacle Learning Center Ultrasound Uses - Medical Images • The ultrasound is sent into the patients body. • At each boundary between different tissues or organs some of the ultrasound is reflected. • The depth of each layer is calculated using the time taken for each reflected wave to return. • The reflected waves (echoes) are usually processed to produce a picture of the inside of the body on a screen.
  • CC20P Copyright – Pinnacle Learning Center • The ultrasound waves used to image babies and soft tissue organs have small amplitude so are low energy. • This makes it safer for the patient, as no damage is done to any living cells. • The alternative is X-rays which are high energy electromagnetic waves and which have enough energy to damage or kill human cells. Ultrasound Uses - Medical Images
  • CC20P Copyright – Pinnacle Learning Center Ultrasound Uses - Medical Images • Ultrasound can also be used to break down kidney stones – high energy shockwaves can be aimed precisely at the kidney stone, breaking it down allowing the body to remove them This means the patient does not need surgery, and is relatively painless
  • CC20P Copyright – Pinnacle Learning Center Ultrasound Uses - Pre-Natal Scanning • Ultrasound waves pass through some materials better than others
  • CC20P Copyright – Pinnacle Learning Center Ultrasound Uses - Pre-Natal Scanning 1. Different parts of the body reflect the sound waves differently (echoes) 2. A computer picks these reflected waves up, and processes them into a image so we can see inside the womb 3. It is not known for sure if ultrasound is entirely safe, but it is certainly safer than using X- rays!
  • CC20P Copyright – Pinnacle Learning Center Ultrasound Uses - Sonar • Some animals have been using ultrasounds for millions of years • Humans have only recently taken advantage of ultrasounds, and although we cannot hear the sounds, we can use equipment to make and detect these signals Ultrasounds are produced, and a computer analyses how long the sound reflections (echoes) take to get back to a detector – this enables you to calculate the distance of certain objects
  • CC20P Copyright – Pinnacle Learning Center Ultrasound Uses - Sonar • Sonar equipment sends out a pulse of sound (ping) – the sound is reflected off objects, and the echo of the sound returns • The time taken for the echo to return is measured, and the distance calculated This is used by boats to identify the depth of the seabed; fish finding; and by the military, especially within submarines (this is how they ‘see’ where they are going)
  • CC20P Copyright – Pinnacle Learning Center Ultrasound Uses - Using Sonar • Sonar equipment is used to send out a wave at a given wavelength at frequency above 20,000 Hz. • This can be timed to see how long it takes to hit the fish and be reflected back. • The equation speed = frequency x wavelength can be used to calculate speed. • The results can then be put into the speed = distance/time equation.
  • CC20P Copyright – Pinnacle Learning Center Used to monitor animal movement Used to study Volcanoes Frequency of less than 20Hz More than 20000 Hz Are absorbed by material more easily Used by some animals to communicate Longitudinal Require a medium Travel faster in Denser medium SimilaritiesDifference Difference Infrasound Ultrasound Infrasound vs Ultrasound
  • CC20P Copyright – Pinnacle Learning Center How can the fisherman locate the position of the fish? Quiz • They can use the speed = frequency x wavelength and speed = distance/time • Remember it is there and back so the answer needs to be halved.