Waves
A repeating disturbance or movement that transfers energy through matter or space.
A wave will travel as long as it has energy.
Mechanical Waves
Mechanical Wave: is a disturbance in matter that carries energy from one place to another.
Mechanical waves require matter to travel Medium: is a material (matter) that
mechanical waves travel through solid liquid or gas. Ex. Air, water, aluminum, copper,
The speed of mechanical waves changes with different mediums
Mechanical wave is created when a source of energy causes a vibration to travel through a medium
Vibration: a repeating motion that follows a pattern
Sound is created by vibrations Vocal cords
There are 3 types of mechanical waves Transverse waves Longitudinal waves/ Compressional Surface waves
Longitudinal Transverse
Transverse waves: is a wave that causes the medium to vibrate at right angles (perpendicular) to the direction in which the wave travels
Up & Down, or Side to Side motion Draw a picture of a transverse wave Ex.
Water Rope Slinky Electromagnetic (radio waves, infrared, etc)
Crest: is the highest point above the resting position (top of the wave)
Trough: is the lowest point below the resting position (bottom of the wave)
Resting position: is the flat position of a wave before it starts moving Slinky demo
B. Transverse Waves
Wave Anatomy
crests
troughswavelength
wavelength
amplitude
amplitude
corresponds to the amount of energy carried by the wave
nodes
Longitudinal waves: is a wave in which the vibration of the medium travels parallel to the direction of the wave\ Slinky demo
Compression: a part of a longitudinal wave where the particles are pushed closely together
Rarefaction: a part of a longitudinal wave where the particles are spaced farther apart
C. Longitudinal Waves
Longitudinal Waves (a.k.a. compressional) medium moves in the same direction as wave
motion
C. Longitudinal Waves
Wave Anatomy
rarefaction
compression
wavelength
wavelength
Amount of compression corresponds to amount of energy AMPLITUDE.
Surface wave: is a wave that has characteristics of both transverse and longitudinal waves
Up & down movement like a transverse Parallel movement of energy like longitudinal Ex.
Ocean Waves Earthquakes (waves through Earth’s surface)
Properties of Waves
Periodic Motion: is motion that follows a repeating pattern
Period: the time period for one interval of movement
Frequency: is the number of complete cycles that pass a point in a given amount of time Frequency of waves are measured in hertz
(Hz)
Wavelength: is the distance of a complete cycle (either crest to crest or trough to trough)
Long wavelength = low frequency Short wavelength = high frequency
D. Measuring Waves
Frequency ( f ) # of waves passing a
point in 1 second
Hertz (Hz)
shorter wavelength = higher frequency = higher energy
1 second
D. Measuring Waves
Velocity ( v ) speed of a wave as it moves forward depends on wave type and medium
v = wave λ × f V:velocity (m/s) λ:wavelength (m)
ƒ: frequency (Hz)
WORK:v = λ × f
v = (3.2 m)(0.60 Hz)
v = 1.92 m/s
D. Measuring Waves
EX: Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz.
GIVEN:
v = ?
λ= 3.2 m
f = 0.60 Hz
λ
v
f
WORK: f = v ÷ λ
f = (5000 m/s) ÷ (417 m)
f = 12 Hz
D. Measuring Waves
EX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency?
GIVEN:
λ = 417 m
v = 5000 m/s
f = ?
λ
v
f
Wave Speed = wavelength X frequency
Wave speed changes in different mediums
If waves are traveling the same speed, then wavelength and frequency are INDIRECTLY related
Amplitude: is the distance from the resting position to either a crest or trough
Energy and amplitude are DIRECTLY related High energy = high amplitude Low energy = low amplitude
Amplitude in sound is called volume
Light waves travel faster than sound Sound waves travel faster in liquids and
solids than gas Light waves travel faster in gases and
vacuums than in liquids an solids.
Behavior of Waves
Reflection: is when a wave bounces off a surface it can not pass through
Reflection does not change the speed or frequency (the wave can be flipped upside down or side to side) Ex. Mirror
Law of Reflection: the angle of incidence (incoming wave) = the angle of reflection (outgoing wave)
All waves can be reflected The reflection of sound is called an echo
Refraction: is the bending of a
wave as it enters a new medium Ex. light waves
Ruler in a beaker of water Ex. sound waves
Listening to sound underwater
Diffraction: is the bending of a wave as is moves around an obstacle or passes through a narrow opening
Page 510 Eddy: is an area behind a mid-stream boulder
where the water flows in a reverse direction (provides safety for rafters)
Chute: is an area of a river where the water is constricted to a narrow passage
Constructive Interference: is when 2 or more waves combine to form a wave with a larger displacement (amplitude)
Destructive interference: is when 2 or more waves combine to form a wave with a smaller displacement (amplitude) add together
Standing wave: is wave or waves that appear to stay in the same place
Plucking a guitar string Waves in a river Node: is the point on a standing wave where
there is no displacement (amplitude) Antinodes: are the crests and the troughs on
a standing wave
17.4 Sound Waves
Sound waves are longitudinal waves The speed of sound changes due to different
types of mediums Chart 514 Speed: is the distance traveled in a certain
amount of time Meters/second: m/s
Intensity: depends on the amplitude (volume) and the distance from the source
Decibels: (dB) is the unit for sound intensity Chart on 515 Damage to ears around 120 dB
Frequency: is the number of wave cycles to pass a given point in one second
Measured in hertz (Hz) Pitch: is the perceived frequency of sound Different notes in music All the different notes have a unique
frequency
Ultrasound: use sound to locate objects or create pictures
SONAR, fish finders, radar Animals use “echo-location” Bats, dolphins, whales Pregnant ladies get ultra sounds to check the
baby’s health
Doppler Effect: pitch changes due to the object creating the sound moving closer or farther away
Pic on 516
Human Ear
Picture on 517 Outer ear: the collect and funnel the sound
waves into the middle ear Middle ear: amplifies the the vibrations Inner ear: are where nerve endings receive
and send the signal to the brain The brain interprets those signals as sound
Resonance: waves of the same frequency combine (constructive interference)
amplifies the sound Resonance can also cause to vibrate Every object has a natural frequency, if a
sound wave with the same frequency hits it, it will cause the object to vibrate
Seismic waves
Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.