Download types 2 - Greeley Schools

Physics of waves
Study these and the other properties of waves for the test3/11
Definition
• A form of energy transfer between objects, or that which transmits
energy
- mechanical requires a medium to transmit the energy
through
- non-mechanical does not require a medium to transmit
energy
Types of waves
types 1: classed by medium
• mechanical
• electromagnetic
• gravitational
• matter waves
types 2: classed by orientation of change
• transverse
• synonyms
• shear
• examples:
• light and all electromagnetic waves
• musical instruments
• chordophones - vibrating strings (violin, guitar, piano)
• membranophones - vibrating membranes (drums, vocal chords, kazoo?)
• idiophones - vibrating solid object (bells, glockenspiel, xylophone, mbira)
• seismic
• secondary (S) shear
• animal locomotion
• vertebrates (snakes, fish)
Parts
• crest: the high, the greatest positive displacement
• trough: the low part, the lowest negative displacement
Type 2
• longitudinal,
• synonyms
• pressure, compression, density
• examples
• sound
• musical instruments
• aerophones - vibrating columns of air (horns, whistles, organ pipes )
• seismic
• primary (P) pressure
• animal locomotion
• invertebrates (worms)
• traffic jams
• density waves in spiral galaxies generate the arms
Parts
• compressions (a.k.a. condensation): the pressed part, the greatest positive pressure
change, a region where the medium is under compression
• rarefactions (a.k.a. dilations): the stretched part, the lowest negative pressure change, a
region where the medium is under tension
type Surface ocean wave
• http://physics.info/waves/
• surface, interface, complex
• ocean
Type 2
• seismic waves come in two basic families
• body waves, which have already been discussed
• Primary (longitudinal, compression, Pressure)
• Secondary (transverse, Shear), can't propagate through liquids
• surface waves, which are what this discussion is a part of
• Love, (Lateral shear)
• Rayleigh, (elliptical, plate waves, ground Roll), something like ocean waves, but elliptical
instead of circular
Type 2
• torsional
• ribbons, plates, bars
• bridges, skyscrapers
• unclassifiable
• animals
•
•
•
•
arthropod locomotion (centipedes, millipedes, caterpillars)
peristalsis
nerve impulses
heart contractions
• dominoes
types 3
classified by duration
• episodic
• periodic
speed, amplitude, wavelength, period, phase, frequency
seismic energy propagates through the Earth within the 50 Hz to
0.001 Hz range! The expression "long period" (greater than 10 seconds)
and "short period" (less than 1 second or greater than 1 Hz)
types 4
classified by appearance
• traveling
• standing
Summary
• Properties
• A wave is a disturbance that propagates through a medium.
• Propagation describes the spreading of a disturbance.
• Waves transfer energy, momentum, and information, but not mass
• Classifying waves by medium
• Mechanical Waves
• Matter is the medium.
• Sound is a mechanical wave.
• Electromagnetic Waves
• Electric and magnetic fields are the media.
• Light is an electromagnetic wave.
• Gravitational Waves
• The gravitational field is the medium.
• The existence of gravitational waves has not yet been confirmed
Mechanical vs electromagnetic waves
Two-dimensional representation of
gravitational waves generated by
two neutron stars orbiting each other
Radio spectrum
Commercial radio 300MHz
Frequency
Wavelength
Designation
Abbreviation[6]
3–30 Hz
105–104 km
Extremely low frequency
ELF
30–300 Hz
104–103 km
Super low frequency
SLF
300–3000 Hz
103–100 km
Ultra low frequency
ULF
3–30 kHz
100–10 km
Very low frequency
VLF
30–300 kHz
10–1 km
Low frequency
LF
300 kHz – 3 MHz
1 km – 100 m
Medium frequency
MF
3–30 MHz
100–10 m
High frequency
HF
30–300 MHz
10–1 m
Very high frequency
VHF
300 MHz – 3 GHz
1 m – 10 cm
Ultra high frequency
UHF
3–30 GHz
10–1 cm
Super high frequency
SHF
30–300 GHz
1 cm – 1 mm
Extremely high frequency EHF
300 GHz – 3000 GHz
1 mm – 0.1 mm
Tremendously high
frequency
THF
Electromagnetic wave
Classifying waves by orientation
• Transverse Waves
•
•
•
•
The disturbance is perpendicular to the direction of propagation.
All electromagnetic waves are transverse. This includes light.
A crest is a point of maximal change in the positive direction.
A trough is a point of maximal change in the negative direction.
• Longitudinal Waves
•
•
•
•
The disturbance is parallel to the direction of propagation.
Sound is a longitudinal wave.
A compression or condensation is a region where the medium is under compression.
A rarefaction or dilation is a region where the medium is under tension.
Classifying waves by orientation
• Surface Waves or Complex Waves
• A combination transverse–longitudinal wave that forms near the surface of some media.
• Deep water waves are surface waves.
• Torsional Waves
• The disturbance causes the medium to twist
Classifying waves by duration
• adj. episodic; noun pulse
• The disturbance is momentary and sudden.
• adj. periodic, harmonic; noun wave train
• The disturbance repeats at regular intervals
Classifying waves by appearance
• Traveling Waves
• Appear to move.
• Standing Waves
• Do not appear to move
Characteristics of periodic waves
• Amplitude (A)
• The maximum absolute value of a periodically varying quantity.
• Amplitude has the unit of the quantity that is changing (ex. displacement, pressure,
field strength, etc.)
• Period (T)
• The time between successive cycles of a repeating sequence of events.
• T = t/n (time per number of cycles)
• The SI unit of period is the second [s].
• Frequency (ƒ)
•
•
•
•
The number of cycles of a repeating sequence of events in a unit interval of time.
ƒ = n/t (number of cycles per time)
Frequency and period are reciprocals (or inverses) of one another: ƒ = 1/T.
The SI unit of frequency is the hertz [Hz = 1/s = s−1].
• Phase (ϕ)
• The stage of development of a periodic process.
• Two points on a wave with the same phase have the same…
• quantity of disturbance (ex. displacement) and
• rate of change of disturbance (ex. velocity).
• Phase is an angular quantity.
• Adjacent points in phase are separated by one complete cycle.
• Adjacent points out of phase are separated by half a cycle.
• The SI unit of phase is the radian, which is itself a unitless ratio
[rad = m/m = Pa/Pa = (V/m)/(V/m) = etc.].
• Wavelength (λ)
• The distance between any point on a periodic wave and the next nearest point
corresponding to the same portion of the wave.
• Wavelength is measured between adjacent points in phase.
• The SI unit of wavelength is the meter [m].
• Speed (v)
• Waves propagate with a finite speed (sometimes called the wave speed) that depends
upon…
• the type of wave,
• the composition of the medium, and
• the state of the medium
• v = Δs/Δt the rate of change of distance with time by definition.
• v = ƒλ the product of frequency and wavelength for periodic waves.
• Frequency and wavelength are inversely proportional.
• Lower frequency waves have longer wavelengths.
• Higher frequency waves have shorter wavelengths.
• The speed of a wave is sometimes known as its wave speed.
• The SI unit of speed is the meter per second [m/s].
One-dimensional wave equation
• ◦linear version
• ƒ(x, t) = A sin(2π(ft − x/λ) + ϕ)
• A = amplitude
• ƒ = frequency
• λ = wavelength
• ϕ = phase
• ◦angular version
• ƒ(x, t) = A sin(ωt − kx + ϕ)
• A = amplitude
• ω = angular frequency (temporal frequency), ω = 2πƒ
• k = wave number (spatial frequency), k = 2π/λ
• ϕ = phase
• http://www.wsfcs.k12.nc.us/Page/5693