Download waves - Fort Thomas Independent Schools

WAVES: basics
Chapters 25.1-25.8; 26
Simple Harmonic Motion
The equal or balanced back and forth or side to
side motion of a particle that is caused to
vibrate by a disturbance.
Similar to a pendulum’s motion.
http://www.physics.uoguelph.ca/tutorials/shm/
Q.shm.html
WHAT IS A WAVE?
A repeating disturbance that causes
vibrations and transmits energy through
matter or space.
WHAT IS THE PURPOSE OF
A WAVE?
To transmit energy from one place to
another.
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)
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.
ARE THERE DIFFERENT
TYPES OF WAVES?
Mechanical Waves
Non-Mechanical Waves
Sound waves
microwaves
Mechanical Waves
Waves that can only travel
through matter
Examples: 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)
Non-Mechanical Waves
Waves that can travel through
matter or space (a vacuum)
Example: electromagnetic
radiation (waves) or light
In general, non-mechanical waves
travel fastest through a vacuum,
then slower through gases, then
liquids and slowest through solids
Two perpendicular transverse
waves
Electromagnetic Wave
http://www.nrc-cnrc.gc.ca/obj/inmsienm/images/research_images/optical_comb/COMBFIG1.gif
Wave Speed
Wave speed (depends upon the
composition and character of the
medium it travels through)
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.acs.psu.edu/drussell/demos/waves/w
avemotion.html
http://www.youtube.com/watch?v=Rbuhdo0AZ
DU
TRANSVERSE WAVE
crest
One
wavelength
amplitude
trough
Rest
position
Compressional (or longitudinal)
Wave
Rarefaction
(less dense)
Compression
(more dense)
one
wavelength
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 wavelengths
Period (P) (the time it takes for one wave
cycle to pass)
Seconds (s)
The lower the frequency, the longer the
period
Wave Characteristics
Wavelength 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.
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
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)