Chapter 15
WAVES
Waves
• Wave - a disturbance that transfers energy
through matter or a medium.
Waves
- waves transfer energy
http://www.youtube.com/watch?v=Y
dnv2xo9Ndw
-Most waves are caused
by vibrating objects.
Types of Waves
1. Mechanical wave -
a wave that requires a medium to
travel through.
Ex. Sound, ocean waves,earthquake waves
Types of Waves
2. Electromagnetic
wave -
a wave that does NOT
require a medium to
travel through.
- these pass though by
magnetic fields or
electromagnetic fields
Ex. light
Wave Forms
1. Transverse waves -
a wave that causes the particles to vibrate
perpendicular to the direction the wave travels
Ex.
Stadium wave, radio waves,
Heat waves,
Wave Forms
2. Longitudinal waves -
a wave that causes the particles of the medium
to vibrate parallel to the direction the wave
travels.
Ex.
Sound wave, compression wave
Wave Forms
3. Surface waves -
– particles move both perpendicular and
parallel to the direction in which the wave
travels.
Ex.
Sound Wave
Sound wave -
– require a medium to travel through.
- longitudinal waves
- causes the particles of the medium to vibrate
parallel to the direction the wave travels.
Wave Properties
• WavelengthThe distance between
any one point on a
wave to an identical
point on
next wave.
Determines the
type and color of
the wave.
Wave Properties
- crest
The top of a
wave
- troughThe bottom
of a wave
Wave Properties
• Amplitude
Half the distance
from the crest and
the trough.
- determines
the loudness
of the sound.
Wave Properties
• period The time it takes a complete
wavelength or wave oscillation to occur.
- same distance as the wavelength.
Wave Properties
• frequency How many waves created in a given
time; the number of cycles or vibrations
in a given time.
- SI label is Hertz (Hz)
- determines the pitch of the sound.
- high frequency = high pitch.
Frequency wave
Wave Speed
• Wave speed (v)- the speed of a wave is
equal to wavelength divided by period, or
frequency multiplied by wavelength.
Two ways you can find wave speed:
- wave speed (v) = wavelength/period
OR
v = frequency x wavelength
Wave Speed
• Ex. Waves passing by a pier have a
frequency of .5 Hz and a
wavelength of 10 m. What is the
wave speed?
Determinates of wave speed:
-The medium determines the speed of the wave.
Ex. Sound: travels fastest in solid (15-20 x faster than air)
travels fast in liquid
travels slowest in air (about 340 m/s)
Ex. Light: travels fastest in empty space
(c = 3 x108 m/s or 186,000 mi/s)
slows down when it has to go through air or water
Determinates of wave speed:
Kinetic energy explains this.
In air, molecules are far apart and won’t hit one
another quickly.
In solids, they are very close and will
easily hit (vibrate) one another.
Doppler Effect
• Doppler effect – an observed change in
frequency of a wave when the source or
observer is moving.
Doppler Effect
• As the ambulance is coming towards you,
the siren sound is hitting you quicker, so the
pitch is higher. As the ambulance is going
away from you, the siren sound is going
away, so it takes longer to hit your eardrum,
so the pitch is lower.
http://videos.howstuffworks.com/discovery/27963assignment-discovery-doppler-effect-video.htm
Wave Interactions
• What happens when a wave meets an object
or another wave?
– Waves can reflect, diffract, refract or interfere
Reflection
• Reflection-The bouncing back of a wave
when it meets a surface or boundary
• Examples:
– Water waves reflect off the side of a boat
– Light waves reflect off
the surface of a lake
Diffraction
• Diffraction-A change in the direction of a
wave when the wave meets an obstacle (ex.
An opening)
• Examples:
– Sound waves diffract around corners
– Water waves diffract around rocks
http://phet.colorado.edu/en/simulation/waveinterference
Refraction
• Refraction-The bending of a wave
when it passes between 2 mediums
in which the speed of the wave
differs
• Example: Straw in water
Interference
• Interference-The combination of 2 or
more waves that result in a single
wave
Interference
• Constructive interference-The
combination of 2 or more waves that
produce a wave with an increased
amplitude
• Destructive interference-The combination
of 2 or more waves that produce a wave
with a decreased amplitude
Interference
Interference: Sound Waves
• Interference of sound waves
produce beats
– Beats-A pattern of alternating loud and
soft sounds
Interference: Light Waves