Waves
What is a wave?
• A repeating disturbance or movement that
•
•
transfers energy through matter or space
Waves transfer energy not matter.
Waves can only exist as they have energy to
carry.
– The water waves to the
right are carrying energy but
are not moving.
What are mechanical waves?
• They require a medium.
– A medium is a form of matter (a substance or
material) through which the wave travels and it can
be a solid, liquid or gas.
• They are not capable of transmitting its energy
through a vacuum (empty space), such as light
from the sun
What are mechanical waves?
• They are produced when a source of energy
causes a medium to vibrate.
– Vibration is a repeated back and forth or up and
down motion
• There are two types of mechanical waves based
on how the wave moves:
– Transverse Waves
– Longitudinal Waves
Transverse Waves
• The matter vibrates perpendicular (at right
angles) to the direction of the wave
– Electromagnetic waves and light waves
Animation courtesy of Dr. Dan Russell, Kettering University
Transverse Wave Properties
• The crest is the highest point
• The trough is the lowest point
• The rest position is the
horizontal line representing the
rope (medium) before it was
disturbed.
• The wavelength is the distance
from one point on the wave to
the next corresponding
adjacent point, such as crest
to crest or trough to tough
Longitudinal Wave
• The matter vibrates parallel (same) to the
direction of the wave
– sound waves
Animation courtesy of Dr. Dan Russell, Kettering University
Longitudinal Wave Properties
• The area squeezed
together is called
compressions like the
crests on a transverse
wave
– In the picture, where the
parts of the medium (coils
of the Slinky) are closer
together than normal
• The areas spread out are
called rarefactions like
the troughs on a
transverse wave
– In the picture, where the
parts of the medium are
farther apart than normal
Sound Waves
• Sound is a longitudinal
•
wave which travels
through the air through a
series of compressions
and rarefactions.
Sound travels through air,
but travels through other
materials as well.
What is echolocation?
What is sonar?
• Sonar is a system that uses the reflection of
underwater sound waves to detect objects. This
has been used to find sunken ships and schools
of fish.
What are seismic waves?
• An energy wave which vibrates
through the earth’s crust as
the crust bends or breaks.
• Seismic waves exist as
transverse (secondary waves),
longitudinal (primary waves)
and both types (surface) of
waves.
• Some travel through the earth
(P and S waves) and some
travel across the earth’s
surface (surface waves).
Animation courtesy of Dr. Dan Russell, Kettering University
Surface Waves
• A combination of longitudinal & transverse
Animation courtesy of Dr. Dan Russell, Kettering University
Amplitude
• The amplitude of a wave is
directly related to the energy
of a wave.
• The amplitude of a longitudinal
wave is determined by the
closeness of the
compressions. The closer the
compressions and the farther
the rarefaction lines.
• The amplitude of a transverse
wave is determined by the
height of the crest or depth
of the trough.
Wavelength and Frequency
• Wavelength is the distance between two corresponding
•
parts of a wave.
Transverse wave: a measure of distance from crest
to crest or trough to trough
• Longitudinal wave: a measure of the distance
between one compression and rarefaction to the
next
• Frequency is the number of waves that pass through a
point in a certain amount of time.
– The unit for frequency is waves per second or Hertz (Hz).
– One Hz = One wave per second.
Wavelength and Frequency
• Wavelength and frequency are inversely
related.
• A decrease in the wavelength, means the
more times the wave will pass through a
point in one second (an increased
frequency).
• The larger the wavelength (or increased
wavelength), the fewer times it will pass
through a point in one second (a
decreased frequency).
Electromagnetic Waves
• Wave which is capable of transmitting its
energy through a vacuum (i.e., empty
space)
• Produced by the vibration of electrons within
•
atoms on the Sun's surface
Travel through space until they reach Earth