Download Waves What Are Waves? Definitions: A wave is a temporary

Name: ___________________________________
Date: ___________________________________
Flynt - ___ Period
____th Grade Science
I.
Waves
A. What Are Waves?
1. Definitions:
 A wave is a temporary disturbance that transfers energy from place to place,
usually through some kind of medium (matter).
 An oscillation (back and forth or up and down) that carries energy from one
place to another with a certain velocity (speed and direction).
2. Parts of a Wave
 Crest – peak or highest point on a
wave
 Trough – valley or lowest point
between two crests.
 Equilibrium or resting position
– the midline between the crest
and the trough of a transverse
wave. Always parallel to the
direction of energy propagation.
 Compression – the parts of a longitudinal wave where the particles of the
medium are pressed close together. Corresponds to the crest of a transverse
wave.
 Rarefaction – the part of a longitudinal wave where the particles of the
medium are spread far apart.
3. Ways to Measure and Describe Waves
 Direction of Propagation – the direction in which the energy of the wave
travels.
SUMMARY
3. Ways to measure and Describe Waves (cont.)
 Wavelength – the distance from a point on one wave to the exact same point
on the next wave.
 Usually measured from the crest of one wave to the crest of the next wave,
(or from trough to trough).
λ = velocity (m/s)
frequency (Hz)
 Amplitude – the maximum distance the
particles of a medium move away from their
resting position as a wave passes through
the medium.
 Basically, amplitude is the height of a
wave above the midline resting position.
 Frequency – the number of complete waves
(oscillations) that pass a given point in
certain amount of time. Measured in units
called Hertz (Hz), which stands for cycles
per second.
ƒ = # of waves
time
B. Classifying Waves Based on MEDIUM: Waves can be
classified as to whether or not they can
move/propagate through a vacuum. Thus, there are
two options: waves that can and waves that can’t.
1. Mechanical Waves: waves that require a medium in order to propagate energy.
 MECHANICAL waves MUST move through a MEDIUM, (which is MATTER).
 Medium – the material (matter) through which a wave travels; can include
solids (like rocks of Earth’s crust), liquids (like ocean water), gasses (like the
atmosphere), etc.
 Examples of mechanical waves: sound waves, ocean waves, seismic waves,
stadium waves.
2. Non-Mechanical Waves: waves that can propagate energy in the absence of a
medium.
 Non-Mechanical waves do NOT need a medium in order to transmit energy (can
move through a vacuum).
 ELECTROMAGNETIC WAVES: all forms of light can move through the vacuum
of space!
SUMMARY
C. Describing/Classifying Waves Based on STRUCTURE:
All waves are classified/divided into three main types
based on their structure: longitudinal, transverse, or
combination.
1. Longitudinal (Compression) Waves – one of
the 3 main types of structural waves; for waves of
this type, the particles in the medium oscillate back
and forth parallel to the direction in which the wave
energy travels (direction of propagation).
 Example #1: Primary Seismic Waves (P-Waves)
 P-waves are mechanical longitudinal seismic waves.
 P-waves are the fastest earthquake waves.
 P-waves arrive at distant locations and are recorded by seismographs
before other types of seismic waves.
 P-waves are made up of compressions and rarefactions of the rock inside
the earth (rock is the medium).
 P-waves can propagate through a fluid medium.
 Example #2: Sound Waves
 Waves produced when an initial “source” object vibrates.
 The vibrating object compresses the particles in the matter next to it,
creating compression waves that move outward in all directions away from
the source.
 Unlike light waves, sound
waves need a medium
(matter) to travel through.
Sounds cannot travel through
a vacuum!
 In general, sound travels
faster through solids than
through liquids, and faster
through liquids than through
gasses.
SUMMARY
2. Transverse Waves – one of the 3 main types of structural waves; for waves of this
type, the particles in the medium oscillate perpendicular to the direction in which the
wave energy travels (direction of propagation).
 Example #1: Secondary Seismic Waves (S-Waves)
 S-waves are mechanical transverse seismic waves.
 S-waves cannot travel through liquids.
 Since the Earth’s outer core is liquid, s-waves cannot pass through the
core region and will not be detected on the side of the Earth opposite
the quake.
 The disappearance of s-waves is actually some of the first indirect
evidence that was used to support the theory that the outer core is
liquid!!!
SUMMARY
2. Types of Transverse Waves (cont.)
 Example #2: Electromagnetic Waves (Light Waves)
 Electromagnetic waves are non-mechanical transverse waves. They can
move through matter and through a vacuum (do not require a medium).
 Light (electromagnetic waves) is actually a kind of travelling
disturbance in the electromagnetic field!
 Electromagnetism is the physics of the electromagnetic field: a field,
encompassing all of space, composed of the electric field and the magnetic
field.
 The electric field can be produced by stationary electric charges, and
gives rise to the electric force, which causes static electricity and
drives the flow of electric current in electrical conductors.
 The magnetic field can be produced by the motion of electric
charges, such as an electric current flowing along a wire, and gives
rise to the magnetic force one associates with magnets.
 The term "electromagnetism" comes from the fact that the electric and
magnetic fields are closely intertwined, and, under many circumstances, it
is impossible to consider the two separately.
 For instance, a changing magnetic field gives rise to an electric field
(and vice versa); this is the phenomenon of electromagnetic induction,
which underlies the operation of electrical generators, induction
motors, and transformers.
 Electromagnetic waves are composed of two fields: an electric field
coupled with a magnetic field.
 The magnetic and electric fields of an electromagnetic wave are
perpendicular to each other and to the direction of wave propagation.
SUMMARY
Types of Transverse Waves: Electromagnetic Waves (cont.)
 The force that an electromagnetic field exerts on electrically charged
particles, called the electromagnetic force, is one of the four fundamental
forces in nature.
 The other fundamental forces are the strong nuclear force (which holds
atomic nuclei together), the weak nuclear force (which causes certain
forms of radioactive decay), and the gravitational force.
 All other forces are ultimately derived from the four fundamental
forces. However, it turns out that the electromagnetic force is the
one responsible for practically all the phenomena we encounter
in daily life, with the exception of gravity!

Roughly speaking, all the forces involved in interactions between
atoms can be traced to the electromagnetic force acting on the
electrically charged protons and electrons inside the atoms. This
includes the forces we experience in "pushing" or "pulling"
ordinary material objects, which come from the intermolecular
forces between the individual molecules in our bodies and those
in the objects (i.e. tension, compression, elasticity, viscosity,
etc.).

The electromagnetic force is also the responsible for all forms of
chemical properties, which arise from interactions between
electrons surrounding the nuclei of atoms.
 So to reiterate: Light (electromagnetic waves) is actually a kind of
travelling disturbance in the electromagnetic field!
 Types of electromagnetic (light) waves:
 Gamma Rays
 X-Rays
 Ultraviolet Waves (UV Light)
 Visible Light
 Infrared Light
 Microwaves
 Radio Waves
SUMMARY

Electromagnetic (transverse) Waves (cont.)
 James Clerk Maxwell and Heinrich Hertz are two scientists who studied
how electromagnetic waves are formed and how fast they travel.
 Electromagnetic waves can be described by their wavelengths, energy, and
frequency. All three of these things describe a different property of light,
yet they are related to each other mathematically.
 X-rays and gamma-rays are usually described in terms of energy (in
units of electron-volts, or eV).
 Optical (visible) and infrared light are usually described in terms of
wavelength. Wavelengths of optical light have units of nanometers
(nm). One nm is equal to one billionth of a meter.
 Radio waves are usually described in terms of frequency using units
called Hertz (Hz), which stands for cycles per second.
SUMMARY
3. Combination/Surface Waves – one of the 3 main types of structural waves;
waves of this type involve a combination of both longitudinal and transverse motions
as wave energy moves along a boundary
between mediums of two different phases.
 Water Waves
 Occur at the boundary between a
liquid (like the ocean) and a gas
(like the atmosphere).
 As a wave travels through the
water, the water particles travel
in clockwise circles.
 The radius of the circles decreases as the depth into the water increases.
 Rayleigh Surface Waves (3rd type of Seismic Waves)
 Occur at the interface between a solid and either a liquid or a gas.
 As a Rayleigh surface wave passes through the particles in a solid, the
particles move in elliptical paths, similar to the circular motion of particles
in a water wave.
 As the depth into the solid increases, the "width" of the elliptical paths
decreases.
 Rayleigh waves are different from water waves in that particles at the
surface trace out a counter-clockwise ellipse, while deeper particles (depth
of more than 1/5 of a wavelength) trace out clockwise ellipses.
SUMMARY
D. Wave Refraction/Speed of a Wave: Typically there are two essential types of properties
that effect wave speed - inertial properties and elastic properties.
 The speed of any wave depends upon the properties of the medium through
which the wave is traveling.
1. Elastic properties are those properties related to the tendency of a material to
maintain its shape and not deform whenever a force or stress is applied to it.
 A material such as steel will experience a very small deformation of shape
(and dimension) when a stress is applied to it.
 Steel is a rigid material with a high elasticity.
 On the other hand, a material such as a rubber band is highly flexible;
when a force is applied to stretch the rubber band, it deforms or
changes its shape readily.
 A small stress on the rubber band causes a large deformation. Steel is
considered to be a stiff or rigid material, whereas a rubber band is
considered a flexible material.
 At the particle level, a stiff or rigid material is characterized by atoms
and/or molecules with strong attractions for each other. When a force is
applied in an attempt to stretch or deform the material, its strong
particle interactions prevent this deformation and help the material
maintain its shape. Rigid materials such as steel are considered to have
a high elasticity. (Elastic modulus is the technical term). The phase of
matter has a tremendous impact upon the elastic properties of the
medium. In general, solids have the strongest interactions between
particles, followed by liquids and then gases. For this reason,
longitudinal sound waves travel faster in solids than they do in liquids
than they do in gases. Even though the inertial factor may favor gases,
the elastic factor has a greater influence on the speed (v) of a wave,
thus yielding this general pattern:
B.
C. vsolids > vliquids > vgases
D. Inertial properties are those properties related to the material's tendency to be sluggish
to changes in its state of motion. The density of a medium is an example of an inertial
property. The greater the inertia (i.e., mass density) of individual particles of the
medium, the less responsive they will be to the interactions between neighboring
particles and the slower that the wave will be. As stated above, sound waves travel
faster in solids than they do in liquids than they do in gases. However, within a single
phase of matter, the inertial property of density tends to be the property that has a
greatest impact upon the speed of sound. A sound wave will travel faster in a less dense
material than a more dense material. Thus, a sound wave will travel nearly three times
faster in Helium than it will in air. This is mostly due to the lower mass of Helium
particles as compared to air particles.
E.
SUMMARY
F.
The speed of a sound wave in air depends upon the properties of the air, mostly the
temperature, and to a lesser degree, the humidity. Humidity is the result of water vapor
being present in air. Like any liquid, water has a tendency to evaporate. As it does,
particles of gaseous water become mixed in the air. This additional matter will affect the
mass density of the air (an inertial property). The temperature will affect the strength of
the particle interactions (an elastic property). At normal atmospheric pressure, the
temperature dependence of the speed of a sound wave through dry air is approximated
by the following equation:
G.
H. v = 331 m/s + (0.6 m/s/C)•T
I. where T is the temperature of the air in degrees Celsius. Using this equation to
determine the speed of a sound wave in air at a temperature of 20 degrees Celsius
yields the following solution.
J.
K. v = 331 m/s + (0.6 m/s/C)•T
L. v = 331 m/s + (0.6 m/s/C)•(20 C)
M.
N. v = 331 m/s + 12 m/s
O.
P. v = 343 m/s
Q.
R. (The above equation relating the speed of a sound wave in air to the temperature
provides reasonably accurate speed values for temperatures between 0 and 100 Celsius.
The equation itself does not have any theoretical basis; it is simply the result of
inspecting temperature-speed data for this temperature range. Other equations do exist
that are based upon theoretical reasoning and provide accurate data for all
temperatures. Nonetheless, the equation above will be sufficient for our use as
introductory Physics students.)
SUMMARY
S. Motion of Ocean Waves
1. Formation of Ocean Waves (How Waves Form)
2. Energy and Particle Motion in Waves (if you didn’t talk about it elsewhere)
T. Wave Interactions (Basics)
1. Reflection
2. Refraction
Include diagrams for these!
3. Diffraction
4. Interference
U. Ocean Waves and Shoreline Interactions
 How Waves Change Near Shore
 How Waves Affect the Shore
 How to Minimize Beach Erosion Due to Waves
SUMMARY