Transcript Chapter 10 Sect. 2

Chapter 10 Sect. 1
The Nature of Waves
Wave—a repeating disturbance or
movement that transfers energy
through matter or space
• Ex: ocean waves (resulting from earthquakes
• Waves carry energy without transporting
matter from place to place. All waves are
produced by something that vibrates. A
wave will travel only as long as it has
energy to carry
Medium-the matter that
waves travel through
• Ex: sound waves through air, etc.
Not all waves need a medium
(light waves)
• Medium can be a solid, liquid, gas
or combination of these
Mechanical
Waves—have to have
a medium to travel (air, water or some other
medium) There are two types:
• Transverse: matter in the medium moves at
right angles to the wave motion (zig-zag
movement) ex: water waves
• Compressional: matter moves in the same
direction as the wave movement (straight line
motion w/no crests and troughs, instead
compressions and rarefactions) ex: sound
waves
Sound waves
• Can travel through air, water, solids like
steel and wood Particles in these
mediums are pushed together and move
apart as sound waves move through them
When a sound wave reaches your ear, it
causes your eardrum to vibrate then
signals messages to your brain
Water Waves
• Not purely transverse waves
• There is a combination of up and
down and back and forth motion
• Therefore, water moves in circles
• (Also: wind speed changes
vibration of the waves)
Seismic waves
• Combinations of compressional
and transverse waves
• They travel through the Earth’s
crust after an earthquake and
cause great damage to houses,
buildings, structures
Section 2:
• Wave Properties
Parts of a Wave
• Crests—the highest points of a
transverse wave
• Troughs—lowest points of a
transverse wave
• (transverse waves have
alternating high pts and low pts)
Compressional waves
• -have no crests and no troughs
• More dense area of the wave—
compression
Less-dense region of the wave-rarefaction
Wavelength
• Wavelength—property of a wave
– The distance between one point on a
wave and the nearest point just like
it.
– (measured from crest-crest or
trough-trough OR compression to
compression or rarefaction to
rarefaction)
Frequency
• Frequency of a wave is the #
wavelengths that pass a fixed
point ea/second.
– Expressed in Hertz (Hz)
– Hertz is the same as 1/s
More on wavelengths
and frequency
• With transverse waves, when
frequency increases, wavelength
decreases
• Frequency of a wave = rate of
vibration of the source that creates
it
Wave Speed
• Speed of a wave depends on the
properties of the medium it is traveling
through
– Ex: sound waves travel faster in liquids and
solids than in gases
– Ex: light waves travel more slowly in
liquids and solids than they do in gases
Calculating Wave
Speed
• Speed = wavelength X
frequency
• OR
• V = wavelength X f (pg. 335)
Amplitude and Energy
• Amplitude—related to the energy
carried by a wave
• The greater the waves amplitude, the
more energy the wave carries
• Amplitude is measured differently for
compressional and transverse waves
Amplitude of
Compressional Waves
• Related to how tightly the medium is
pushed together at the compressions
• Denser medium, larger amplitude,
more energy the wave carries
• The closer the coils are in a
compression, the farther apart they are
in a rarefaction, & the more energy
carried
Amplitude of
Transverse Waves
• Amplitude of a transverse wave
increases as the energy carried by
the wave increases
• A tall ocean wave has a greater
amplitude than a short ocean
wave