TYPES OF MECHANICAL
WAVES AND THEIR
CHARACTERISTICS
Sections 8.2-8.3
Key Terms
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Transverse Wave
Longitudinal Wave
Compression
Rarefaction
Sound
Amplitude
Waveform
Crest
Trough
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Wavelength
Phase
Phase Shift
In Phase
Out of Phase
Frequency
Period
Wave Speed
Simple Harmonic Motion
Types of Mechanical Waves


Mechanical waves can be classified according to
the direction of particle motion compared to the
direction of wave motion.
There are two basic types of mechanical waves
 Transverse
Waves
 Longitudinal Waves
Transverse Waves

A transverse wave is a wave in which the particles
vibrate perpendicular to the direction of the flow of
energy.
 eg.)
a guitar string
 The
string moves in a perpendicular direction to flow of
energy.
 eg.)
water waves
 Objects
axis.
bob up and down y axis as energy moves along x
Longitudinal Waves

A longitudinal wave describes a wave in which the
particles vibrate parallel to the direction of the flow
of energy.
Transverse vs. Longitudinal Waves
Compressions and Rarefactions

Gases have great freedom of movement and are in
constant motion due to their temperature.
 Longitudinal
vibrations in a gas result in:
 Compression

The region in a longitudinal wave in which the particles are closer
together
 Rarefaction

The region in a longitudinal wave in which the particles are
farther apart
Sound

A Vibrating object can produce longitudinal waves
in the medium surrounding it.
 If
the waves are detectable to the human ear, they are
called sound waves.
 Successive compressions and rarefaction of a sound
wave cause vibrations in our tympanic membranes
(eardrums) and our brains interpret this as sound.
Bell in a Bell
Complex Wave Motion

In many cases, transverse and longitudinal waves
combine to form more complex waves.
Wave Characteristics


Some characteristics of waves are based on
geometric features, and some characteristics are
based on time.
Waves can therefore be described in terms of their
size, shape, and the speed at which they move.
Geometric Wave Characteristics

Based on shape and size of wave.
 Amplitude
 Wavelength
 Phase
 Phase
Shift
The Waveform

The shape of a wave when graphed.
Amplitude

The maximum displacement of a wave from its
equilibrium point
Crest

The maximum point of a transverse wave.
Trough


The minimum point of a transverse wave
A continuous wave has many repeating crests and
troughs
Wavelength

The distance between two similar points in successive
identical cycles in a wave.
 Crest
to crest or trough to trough
 Symbol for wavelength is
Phase and phase shift


In a continuous transverse or longitudinal wave, the
x-coordinate of a unique point of the wave is the
phase.
A shift of an entire wave along the x-axis with
respect to an identical wave is a phase shift.
In Phase vs. Out of Phase
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When two identical waves
have the same phase shift
they are in phase
When two identical waves
have different phase
shifts they are
out of phase
If the phase shift is 0.5,
the waves are said to be
completely out of phase.
Time-Based Wave Characteristics

Related to the motion of the vibrating particle and
the wave.
 Frequency
 Period
 Speed
Period

The time for a vibrating particle to complete one
cycle.
Frequency

The number of complete cycles per unit time, usually
1s.
 Measured

in hertz (Hz)
Frequency and period are related
Wave Speed

The rate at which a wave is travelling through a
medium.
 Also
a measure of how fast the energy in the wave is
moving.

Can be calculated if the wavelength and period of
a wave are known.
Simple Harmonic Motion

Any motion that repeats itself at regular intervals.
 Amplitude,
period, and frequency are the same for
each oscillation
8.2 Summary
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In transverse waves, the particles of the medium move
perpendicular to the direction of the flow of energy.
In longitudinal waves, the particles of the medium move
parallel to the direction of the flow of energy.
In a fluid, longitudinal waves transfer energy through
regions of higher and lower pressure. These regions are
called compressions and rarefactions, respectively.
Sound, an important example of a longitudinal wave, is
a form of energy produced by rapidly vibrating
objects.
Many wave motions in nature are a combination of
longitudinal and transverse motion.
8.3 Summary
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Wave characteristics are based on both wave shape and the
behaviour of a wave in time.
Amplitude is the maximum distance a vibrating particle moves from
its equilibrium point.
Wavelength is the distance between two similar points in successive
identical cycles in a wave, such as from crest to crest or trough to
trough.
The phase shift is the amount that one waveform is displaced along
the x-axis from an otherwise identical waveform.
Frequency is the number of complete cycles of a wave that occur per
unit of time (usually 1 s). Period is the time it takes for a vibrating
particle to complete one cycle.
Wave speed is the rate at which a wave travels through a medium.
It is also a measure of how fast the energy in the wave is moving.
Simple harmonic motion (SHM) is any oscillating motion that repeats
itself at regular intervals.
Homework
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Page 384
 Questions
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1-6
Page 387
 Questions
1-5