New Standard
• SPS9: Students will investigate the
properties of waves.
– a. Recognize that all waves transfer energy.
b. Relate frequency and wavelength to the energy of
different types of electromagnetic waves and
mechanical waves.
c. Compare and contrast the characteristics of
electromagnetic and mechanical (sound) waves.
d. Investigate the phenomena of reflection, refraction,
interference, and diffraction.
e. Relate the speed of sound to different mediums.
f. Explain the Doppler Effect in terms of everyday
interactions.
17.1:
Mechanical
Waves
What is a wave?
• When matter is disturbed, energy comes
from the disturbance. This energy is in
the form of a wave.
• A disturbance such as a pulse or shock
produces a wave.
– These disturbances are many times repeated or
periodic, such as a guitar string being struck. This
makes the wave continuous
ALL WAVES
TRANSPORT
ENERGY!
Mechanical Waves
Disturbance in
matter that
carries energy
from one place
to another
Mechanical Waves
• Created when a source of energy
causes a vibration to travel through a
medium.
• Requires a medium to travel through.
• Solids, liquids, and gases
• Classified by the WAY they move
through a medium.
3 Main Types of Mechanical
Waves
•Transverse waves
•Longitudinal waves
•Surface waves
Transverse Waves
• Wave that causes the medium to vibrate
at right angles to the direction in which the
wave travels.
• The wave carries energy from left to right
• The highest point of the wave is the
crest.
• The lowest point of the wave is the
trough.
Transverse Waves
Direction of wave
Crest
Rest
position
Direction of vibration
Trough
Examples of Transverse Waves
• Ripples created when rock is thrown into
water
• Rope tied to a tree
• Motion of a plucked guitar string
• Light waves…also called electromagnetic
waves
• Secondary earthquake waves
Secondary Earthquake Waves
• Come after
Primary Wave
• Cause the ground
to roll
Longitudinal Waves
• Waves in which the vibration of the medium is
parallel to the direction the wave travels.
• An area where the particles in a medium
are spaced close together is called a
compression.
• An area where the particles in a medium
are spread out is called a rarefaction.
Longitudinal Waves
Examples of Longitudinal Waves
• Sound
• Primary
earthquake
waves
• Shock waves
from an
explosion
Surface Waves
• Wave that travels along a
surface separating two media.
• Particles of the medium undergo
a circular motion.
• Ocean waves are the most
familiar kind of surface waves.
17.2: Properties
of Mechanical
Waves
Period
• The time required for one complete
cycle to pass a particular point cycle
is called the period.
1 Period
Frequency
• The number of complete cycles in a given
time.
• Measured in cycles per second, or
hertz (Hz).
•One hertz equals one wave cycle per
second.
Frequency & Energy
Frequency & Energy have a Direct Relationship
High frequency=high energy
Low frequency=low energy
Wavelength
• The distance between a point on one
wave and the same point on the next
cycle of the wave.
–One wave cycle is equal to one
wavelength.
Measuring Wavelength
For a transverse wave, wavelength is measured
between adjacent crests or between adjacent
troughs.
Long wavelength
Short wavelength
Measuring Wavelength
• For a longitudinal wave, wavelength is the
distance between adjacent compressions or
rarefactions.
Frequency & Wavelength
• Inverse relationship
– Increasing the frequency of a wave decreases its
wavelength.
– Low frequency=Long wavelength
– High frequency=Short wavelength
Wave Speed
• Formula:
Speed=Wavelength X Frequency
• Units=meters per second
• Speed of a wave can change if it enters a new
medium but for most waves the speed will
remain constant.
Amplitude
• The maximum displacement of the medium
from its rest position.
– How high the wave rises.
– Intensity.
• Increase in amplitude means the wave carries
more energy.
– This is due to the fact that it takes more energy to
produce a larger wave.
– The more energy the wave has, the more the
medium will be compressed or displaced.
Measuring Amplitude
Amplitude
• Louder sounds have a greater amplitude.
• Brighter lights have a greater amplitude.