Waves!
I. A little vocab…
• WAVE:
– A periodic disturbance in a solid, liquid or gas
• MEDIUM:
– Matter or space through which waves travel
II. Types of waves
1. Waves can be classified by
what they move through
a. Mechanical- Requires a
medium
b. Electromagnetic-Does
not require a medium
– Ex- light waves, radio
waves, ultraviolet waves…
2. Waves can also be classified
by how they move
a. Transverse waves – travel perpendicular to the
direction of the wave
b. Longitudinal waves (aka
compression waves )
travel
parallel to the direction of the wave
Surface Waves: Have BOTH
• Occur at the border
between two mediums…
• Water waves: Particles at
the surface move parallel
and perpendicular (in
circles)
• The ball up and down and
side to side
Draw your pictures
Waves Carry Energy
• Simple Harmonic Motion- When you pull on a single spring, its
mass continues to bounce up and down.
• When pulled down, spring gains PE (elastic) As it moves back up when
released, PE is transferred to KE
• Mass goes past the original starting position
• Back at the top, all energy is transferred to PE (gravitational & elastic PE)
• When it moves down again, energy transfers back to KE and it keeps
going
Damped Harmonic Motion- a vibration
that fades out as energy is transferred
from one object to another
• When pulled down, the
•
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spring gains PE
Again, it will be converted
to KE when released
BUT instead of that KE
staying in that spring, it is
transferred to the next
spring in the line.
Anatomy of a Transverse Wave
Crest:
Trough:
Anatomy of a Longitudinal Wave
Compression:
Rarefaction:
Inquiry Lesson
How do we describe waves?
• Wavelength
• Amplitude
• Period
• Frequency
Wavelength ()
– The distance between two identical parts of a
wave
• The distance btwn 2 crests for a TRANSVERSE wave
or two compressions for a LONGITUDINAL wave.
–
The symbol for wavelenths is ____
Draw 2 waves – one with a long
wavelength and one with a short
wavelength!
Amplitude
–
–
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–
•
Distance from the middle of the wave to the crest
(or half the distance between the crest and the trough)
Larger waves have larger amplitudes and carry
more energy
Sound Energy: The more amps the sound has, the
________________ it will be.
(usually represented by the line denisty for a
compressional wave)
Low amplitude
 Medium Amplitude HIGH Amplitude
Draw 2 waves – one with an
amplitude of 5 mm and one with an
amplitude of 2 mm
Period
• The time required for 1 full wavelength
of a wave to pass a certain point
– Or the time required to complete one
vibration of a particle in a medium
• Represented by “t” (seconds)
Frequency
The number of cycles/wavelengths/vibrations
per unit of time
–
Represented by “f” ; f= 1/t
–
Measured in Hertz (named after Heinrich Hertz – 1888 – 1st
demonstrated the presence of electromagnetic waves)
Equal to vibrations per second (1Hz = 1 vibration/1 second)
–
•
•
You can hear 20 Hz to 20,000 Hz
More vibrations = shorter amount of time for each
1. Draw a wave with a period of .5
seconds and a frequency of 2 Hz
2. Draw 2 waves – one with a high
frequency and one with a low
frequency:
Frequency of Light Spectrum (example)
• Wide range of frequencies and wavelengths
• Your eyes can detect 4.3 x 1014 Hz to 7.5 x 1014 Hz (visible light
range)
• Electromagnetic waves exist at frequencies we can’t see
Remember that each wave
carries energy…
• Higher frequency = more energy and
shorter wavelength…The more
wavelengths per unit time, the more
energy.
Ex- sound waves…
• Sound waves – travel as spherical
waves from a speaker
• Wave front – each circular wave
• As they travel out, the wave front gets
bigger – each front has the same
amount of energy. As the wave front
gets bigger, the energy is spread out
over a bigger area (so that is why these
waves are damaging close-up –close to
speaker or close to light)
Wave speed – how fast a wave
moves
• Speed = wavelength / period
• So…
• Wave speed = frequency x wavelength
(because the period is the inverse of the
frequency
Wave speed depends on medium


Sound waves can travel in air
However, they travel even faster in solids
than in air or water
Example: hitting a metal railing and listening
(you will hear two bangs)
Why?
The first sound comes through the steel rail
itself and reaches you shortly before the
second sound, which travels through the
air.
Wave speed depends on medium

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•
In a gas, particles are farther apart so it takes
longer for them to find each other and bump
into each other - sending the wave
In liquids, particles are closer together so waves
travel faster
In solids, particles are very close together so
waves travel the fastest
Example: Earthquakes
(you don’t need to know
this…yet)
Produce seismic waves
P waves (primary) – travel faster, arrive first,
longitudinal waves (shake everything sideto-side)
S waves (secondary) – slower, carry more
energy, transverse waves (shake everything
up and down – more damage)
10. Doppler Effect
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First – pitch is determined by frequency
Sound waves travel out from an object in wave fronts and hit
your eardrum (when they hit your eardrum, they have a
frequency equal to the number of wave fronts that hit your
ear
Ambulance example:
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•
–
When the ambulance moves toward you, the sound waves are
compressed because the ambulance moves a short distance – so
the waves hit your eardrum at a higher frequency – higher pitch
Then, when the ambulance moves away from you, the distance
between the wave fronts is more than before, so the frequency is
lower – pitch is lower
Doppler effect can also happen in light and other types of
waves
• http://physics.bu.edu/~duffy/semester1/c20_wave_spee
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d.html
wave speed different medium
http://www.teachersdomain.org/resource/ess05.sci.ess.
watcyc.wavemotion/
surface wave
http://www.acoustics.salford.ac.uk/feschools/waves/wav
etypes.htm
transverse right angles
http://www.acoustics.salford.ac.uk/feschools/waves/refl
ect.htm#reflect
reflection