Properties of Waves
Chapter 12 Section 3
What Is A Wave?
• Ripple waves in water are formed by the
vibrations of water molecules.
• As the vibration waves spread outward to
more molecules, the waves travel outward.
• A wave is considered to be the motion of
disturbance.
– Particles within the wave vibrate around and
equilibrium position.
Medium
• Medium – Material through which a
disturbance travels.
• In order for a wave to form, it needs a
medium which provides the particles that
vibrate.
– The medium does not travel with the wave
– After the wave passes, the particles return to
their equilibrium position.
• Examples:
– Sound: The medium is air
– Ocean Waves: The medium is water
Mechanical Waves
• Mechanical Waves – A wave whose
propagation requires the existence of a
medium.
• Not all wave propagation requires a
medium
– Electromagnetic waves
Wave Types
• Pulse Wave – A single non-periodic
disturbance.
– A wave that consist of a single traveling pulse.
• Periodic Wave – A wave whose source is
some form of periodic Motion.
– A wave that consist of multiple traveling
pulses.
Sine Waves
•
•
If the source of the wave is in simple
harmonic motion, then the wave mimics
harmonic motion as well.
A wave that is vibrating in simple
harmonic motion is called a sine wave.
– A graph of a trigonometric function produces
this curve when plotted.
•
y = sin x
Transverse Wave
• Transverse Wave – A wave whose
particles vibrate perpendicular to the
direction of wave motion.
– The particles vibrate up and down as the
wave moves from left to right or vise versa.
• Examples:
– Electromagnetic waves
– Ocean waves
– Wave traveling through a rope
Graphing
• Waveform – A waveform can represent
either the displacements of each point of
the wave at a single moment in time or the
displacements of a single particle as time
passes.
– Trigonometric function of sine represents the
wave.
Graphing
• The x-axis represents the equilibrium
position of the wave.
• The y-axis of the curve represents the
displacement of each point on the wave at
time (t).
Describing a Wave
• Crest – The highest point above the
equilibrium position.
• Trough – The lowest point below the
equilibrium position.
• Wavelength – The distance between two
adjacent similar points of the wave, such
as crest to crest or trough to trough.
– Variable for wavelength – λ (Greek letter – Lamda)
• Amplitude – The point at which the
displacement is its maximum distance
away from the equilibrium position.
Transverse Wave Diagram
y
Wave Length
Amplitude
λ
Crest
Displacement
Equilibrium
Position
x
Amplitude
Trough
Longitudinal Waves
• Longitudinal Waves – A wave whose
particles vibrate parallel to the direction of
wave motion.
– The particles vibrate in the same direction as
the direction of the wave.
• Often called density waves or pressure
waves
– Crest are high density
– Trough are low density
• Examples:
– Sound Waves
– Earthquakes
Longitudinal Wave Diagram
Stretched
Density
Longitudinal Wave
Compression
crest
Equilibrium
trough
Transverse Waves vs.
Longitudinal Waves
• Transverse waves oscillate perpendicular to
the direction of the wave propagation.
– Light Waves
• Longitudinal waves oscillate parallel to the
direction of the wave propagation.
– Sound Waves
Link:
• Transverse and Longitudinal Wave Animation
Period and Frequency
• Frequency describes the number of crest
or troughs that pass a given point in a unit
of time.
• Period of a wave is the amount of time
required for one complete vibration of
particles or one wavelength.
Speed of a Wave
• The speed of a wave can be found
through the waves frequency and
wavelength.
• The equation is derived through the linear
kinematic equation for velocity.
Speed of a Wave Equation
𝑣 = 𝑓𝜆
• 𝑣 = 𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑊𝑎𝑣𝑒
𝑚
𝑠
• 𝑓 = 𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝐻𝑧
• 𝜆 = 𝑊𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ 𝑚
• The speed of a mechanical wave remains
constant for any given medium.
• If the frequency increases, the wavelength must
decrease.
• Speed only changes if the medium changes.
Example Problem
• A 2640 Hz whistle produces sound waves
that have a wavelength of 50.0 cm in
water. What is the speed of sound in the
water?
Example Problem Answer
• v = 1320 m/s
Energy and Waves
• The energy is transferred by the motion of
the matter rather than by transferring
matter itself.
– Energy is transferred very efficiently in a
wave.
– Examples:
• Tsunamis
• Sound
• Earthquake
• Greater the amplitude, greater the energy