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Mechanical wave- a disturbance in matter that carries energy from one place to another Require a medium to travel through ◦ A medium can be a solid liquid or gas ◦ In a wave pool, water is the medium
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Mechanical waves are created when a source of energy causes a vibration to travel through a medium
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Transverse waves Longitudinal waves surface waves Demo transverse vs longitudinal
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A transverse wave in which the vibrational displacement is in a perpendicular direction to the motion of the wave - A pulse is a single disturbance in a medium that moves along a wave from one location to another
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Before the wave starts, every point on the wave is in the rest position crest- highest point above the rest position trough- lowest point below the rest position amplitude- the measurement from the rest position to the crest of the wave (height of the wave) frequency- the rate at which a complete wave pulse (a wavelength) pass a point
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Wave interference is the phenomenon that occurs when two waves meet while traveling along the same medium
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Constructive interference is when the two interfering waves have a displacement in the same direction
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Destructive interference – occurs where the two interfering waves have a displacement in the opposite direction
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Longitudinal wave- the vibration of the medium is in the same direction (parallel) the wave travels
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Compression – area where the particles in a medium are spaced close together Rarefaction- area where the particles in a medium are spread out
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Surface wave – travels along a surface separating two media
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types of waves types of waves
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Bill Nye Waves Bill Nye Waves
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Periodic motion- any motion that repeats at regular time intervals Period- the time it takes for one cycle to complete motion that returns to its starting point Any periodic motion has a frequency- number of complete cycles (pulses) that pass a point in a given time ◦ Frequency is measured in cycles/sec or Hz
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Wavelength – the distance between a point on one wave and the same point on another wave ◦ If you increase the wavelength you decrease the frequency
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Wave speed ◦ Speed = distance x time ◦ So the speed of a wave is speed = wavelength x frequency
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One end of a rope is vibrated to produce a wave with a wavelength of 0.25 meters. The frequency of the wave is 3.0 Hz. What is the speed of the wave? 0.75 m/s
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IF you assume that waves are traveling at a constant speed, then wavelength is inversely proportional to frequency
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Amplitude- is the maximum displacement of the medium from its rest position The more energy a wave has, the greater its amplitude
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Reflection- occurs when a wave bounces off a surface that it cannot pass through ◦ If you send a transverse wave down a rope attached to a wall – the wave reflects Reflection does not change the speed or frequency of a wave, but the wave can be flipped upside down
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Refraction- the bending of a wave as it enters a new medium at an angle ◦ This happens because one side of the wave moves more slowly than the other as it enters the new medium
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Diffraction- is the bending of a wave as it moves around an obstacle or passes through a narrow opening A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle
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Interference- occurs when two or more waves overlap and combine together Two types of interference ◦ Constructive ◦ Destructive
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Constructive interference- when two or more waves combine to produce a wave with a larger displacement
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Destructive interference- occurs when two or more waves combine to produce a wave with smaller displacements ◦ one wave’s crest meets another wave’s trough
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interference applet interference applet
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a standing wave is a wave that appears to stay in one place ◦ Only certain points on the wave are stationary- this is known as a node ◦ An antinode- is a point where a crest or trough occurs midway between the two nodes ◦ Demo –slinky ◦ standing wave in a pool standing wave in a pool
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Every object has a natural frequency ◦ The natural frequency of an object is associated with one of the many standing wave patterns which the object could vibrate ◦ The natural frequencies of an instrument are referred to as the harmonics of the instrument The word resonance comes from Latin and means to resound- or sound together with a loud sound
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Tuning fork is used to force the air inside the tube to resonate They create sound waves that go into the opening of the resonance tubes The sound waves vibrate at the same frequency
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Water level can be changed by moving the resonance tube up and down, which changes the length of the air column, and can allow the sound wave to resonate This allows the natural frequency of the airin the tube to be matched by the frequency of the tuning fork The result is a louder sound Ex: seashell
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Harmonic # # of Waves in Column # of Nodes # of Antinodes Length- Wavelength Relationship 11/411λ = (4/1)*L 33/422λ = (4/3)*L 55/433λ = (4/5)*L 77/444λ = (4/7)*L 99/455λ = (4/9)*L
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cool things sound waves can do cool things sound waves can do
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Sound waves are longitudinal waves ◦ Speed ◦ Intensity and loudness ◦ Frequency and pitch
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Why is there a delay when you hear an echo? ◦ In dry air at 20 °C the speed of sound is 342 meters per second
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Intensity- the rate at which a wave’s energy flows through a given area ◦ Measured in decibel (dB) ◦ Exposure to sound more intense than 90 decibels can cause hearing damage Regular speech - 60 decibels Lawn mower – 90 decibels Chain saw – 100 decibels (cause damage after a few minutes) Ear buds @ 70% volume – 85 decibels
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Loudness – a physical response to the intensity of sound ◦ Depends on the health of your ears, and how your brain interprets the sound
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The frequency of a sound wave depends on depends on how fast the source of the sound is vibrating french horn french horn trumpet trumpet
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Pitch- the frequency of a sound as you perceive it ◦ Depends on the frequency of the sound wave ◦ Also depends on your ears, and your age ◦ Most people can hear sounds between 20 Hz and 20,000 Hz ◦ how old are your ears? how old are your ears?
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Infrasound is sound at frequencies lower than most people can hear (long wavelength) Ultrasound is sound at frequencies greater than most people can hear (short wavelength) ◦ Ultrasound used in sonar and imaging ◦ ocean floor mapping ocean floor mapping ◦ Malaysia flight 370 Malaysia flight 370
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The doppler effect- is the change in sound frequency caused by motion of the sound source, the listener or both Doppler effect Doppler effect As the source of sound approaches an observer hears a higher frequency, as the source moves away, the observer hears a lower frequency doppler effect applet doppler effect applet
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Outer ear – part of the ear you can see ◦ Sound waves funnel into the ear canal, then strike the ear drum Middle ear- contails three tiny bones- the hammer, the anvil, and the stirrup ◦ The hammer strikes the anvil which move3s the stirrup back and forth- act as a lever system to amplify the motion of the ear drum Inner ear- vibrations from the stirrup travel into the cochlea ◦ The cochlea is lined with nerve cells which sway back and forth and send signals to the brain
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Sound is recorded by converting sound waves into electrical signals that can be processed and stored ◦ Sound waves vibrate a membrane inside the microphone ◦ The membrane causes a magnet to vibrate, which produces an electronic signal
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Most musical instruments vary pitch by changing the frequency of the standing wave
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