WAVES: basics
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Transcript of WAVES: basics
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WAVES: basics
Chapters 25.1-25.8; 26
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Simple Harmonic Motion
The equal or balanced back and forth or side to The equal or balanced back and forth or side to side motion of a particle that is caused to side motion of a particle that is caused to vibrate by a disturbance.vibrate by a disturbance.
Similar to a pendulum’s motion.http://www.physics.uoguelph.ca/tutorials/
shm/Q.shm.html
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WHAT IS A WAVE?
A repeating disturbance that causes vibrations and transmits energy through matter or space.
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WHAT IS THE PURPOSE OF A WAVE?
To transmit energy from one place to another.
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WHAT HAPPENS TO ENERGY AS THE WAVE
TRAVELS?Energy is transferred from one particle
to the next.The motion of particles in a medium is
like the motion of masses on a spring.Energy of the wave spreads away from
the disturbance or vibration (see white board)
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IS MATTER TRANSMITTED WITH THE WAVE?
No, only energy is transmitted. The particles in the matter vibrate as the
wave passes, but do not travel with the wave.
http://www.infoline.ru/g23/5495/Physics/English/waves.htm
http://members.aol.com/nicholashl/waves/movingwaves.html
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ARE THERE DIFFERENT TYPES OF WAVES?
Mechanical Waves Non-Mechanical Waves
microwavesSound waves
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Mechanical WavesWaves that can only travel through
matterExamples: sound, water and seismic
waves In general, mechanical waves travel fastest
through solids, then slower through liquids and slowest through gases
Can be transverse or longitudinal (or compressional)
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Non-Mechanical WavesWaves that can travel through matter
or space (a vacuum)Example: electromagnetic radiation
(waves) or lightIn general, non-mechanical waves travel
fastest through a vacuum, then slower through gases, then liquids and slowest through solids
Two perpendicular transverse waves
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Electromagnetic Wave
http://www.nrc-cnrc.gc.ca/obj/inms-ienm/images/research_images/optical_comb/COMBFIG1.gif
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Wave Speed
Wave speed (depends upon the composition and character of the medium it travels through)
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Two types of waves based upon direction of vibrating particles: Transverse Waves cause particles
in matter to vibrate perpendicular to the direction of wave travel.
Longitudinal Waves cause particles in matter to vibrate in the same direction of wave travel.
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
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TRANSVERSE WAVE
crest
trough
amplitude
Onewavelength
Rest position
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LONGITUDINAL WAVECompression (more dense)
Rarefaction (less dense)
one wavelength
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Wave Characteristics
Frequency (f) (the number of vibrations that occur in a given time)Hertz (Hz) (# of vibrations per second)High frequency waves produce waves with
short periods and short wavelengthsPeriod (P) (the time it takes for one wave cycle to
pass)Seconds (s)The lower the frequency, the longer the period
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Wave CharacteristicsWavelength λ (lambda) (the distance between one point
on a wave to the next identical point; crest to crest, for example)Meters (m) The lower the frequency, the longer the wavelength
Amplitude (longitudinal waves—the tightness of the compression; transverse waves—the distance from the crest to rest position or from trough to rest position)Meters (m)The greater the amplitude of the wave, the more
energy the wave transfers.
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Frequency vs. Intensity
Rate of vibration (frequency)Amount of energy (intensity)—
Amplitude (amount of displacement)loudness (relative intensity of sound)brightness (number of photons of light)
Turn up the volume--same frequencies, different intensity
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Why do waves become less intense away from the source?
Same amount of energy is spread out over greater and greater distances.
Same energy at every point along a wave front.
Also, simple harmonic motion of the particles can be dampened (or absorbed or transferred) by the medium (rubber, clay, springs, fluids in shock absorbers)