 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

 Mechanical waves are created when a source of energy causes a vibration to travel through a medium

 Transverse waves  Longitudinal waves  surface waves  Demo transverse vs longitudinal

 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

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

 Wave interference is the phenomenon that occurs when two waves meet while traveling along the same medium

 Constructive interference is when the two interfering waves have a displacement in the same direction

 Destructive interference – occurs where the two interfering waves have a displacement in the opposite direction

 Longitudinal wave- the vibration of the medium is in the same direction (parallel) the wave travels

 Compression – area where the particles in a medium are spaced close together  Rarefaction- area where the particles in a medium are spread out

 Surface wave – travels along a surface separating two media

 types of waves types of waves

 Bill Nye Waves Bill Nye Waves

 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

 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

 Wave speed ◦ Speed = distance x time ◦ So the speed of a wave is  speed = wavelength x frequency

 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

 IF you assume that waves are traveling at a constant speed, then wavelength is inversely proportional to frequency

 Amplitude- is the maximum displacement of the medium from its rest position  The more energy a wave has, the greater its amplitude

 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

 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

 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

 Interference- occurs when two or more waves overlap and combine together  Two types of interference ◦ Constructive ◦ Destructive

 Constructive interference- when two or more waves combine to produce a wave with a larger displacement

 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

 interference applet interference applet

 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

 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

 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

 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

 cool things sound waves can do cool things sound waves can do

 Sound waves are longitudinal waves ◦ Speed ◦ Intensity and loudness ◦ Frequency and pitch

 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

 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 70% volume – 85 decibels

 Loudness – a physical response to the intensity of sound ◦ Depends on the health of your ears, and how your brain interprets the sound

 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

 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?

 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

 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

 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

 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

 Most musical instruments vary pitch by changing the frequency of the standing wave