3 Waves Notes 1 - Solon City Schools

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29 Νοε 2013 (πριν από 3 χρόνια και 4 μήνες)

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Waves!

First a little
vocab



WAVE:


A periodic disturbance in a solid, liquid or gas


MEDIUM:


Matter or space through which waves travel



I. Waves transfer energy


Some waves carry more energy than
others


Energy spreads out as a wave travels


Ex
-

sound waves

Ex
-

sound waves…


Sound waves


travel as spherical waves from
a speaker


Wave front


each circular wave of energy


As they travel out, the wave front gets bigger


each front has the same amount of energy. As
the wave front gets bigger, the energy is
spread out over a bigger area






Why don’t you want to sit close to a loud speaker?


When you are close to the speaker (or close to
light) more energy is transferred to your ears (or
eyes)

II. Waves can be classified by what
they move through


a.
Mechanical
-

Requires a
medium


-

ex: ripples on a pond, sound
waves



b. Electromagnetic
-
Does


not require a
medium


Ex
-

light waves
, radio waves,
ultraviolet waves…


Youtube
:
http://www.youtube.com/watch?v=b0JQt4u6
-
XI


2. Waves can also be classified
by how they move


a. Transverse

waves


travel perpendicular to the
direction of the wave




b. Longitudinal waves (aka
compression waves )


travel
parallel

to the direction of the wave


Surface Waves: Have BOTH


Occur at the
border

between two
mediums…


Water waves: Particles at
the surface move
parallel
and
perpendicula
r (in
circles)


The ball up and down and
side to side


Draw your pictures


Youtube

video:


http://ww
w.youtube
.com/watc
h?v=e5tG
aTIW3A8


Anatomy of a Transverse Wave


Crest:


Trough:

Anatomy of a Longitudinal Wave


Compression:





Rarefaction:

Inquiry Lesson


How do we describe waves?


Wavelength


Amplitude


Period


Frequency

Wavelength

(

)



The distance between two
identical

parts of a
wave


The distance
btwn

2 crests for a TRANSVERSE wave
or two compressions for a LONGITUDINAL wave.


The symbol for
wavelenths

is ____



Draw 2 waves


one with a long
wavelength and one with a short
wavelength!


Amplitude



Distance from the middle of the wave to the crest


(or half the distance between the
crest and the trough
)


Larger
amplitudes

and carry more
energy



Ex
-

Sound Energy: The more amps the sound has, the
________________ it will be.


(usually represented by the line density for a
compressional

wave)


Low amplitude



Medium Amplitude

HIGH Amplitude

















Draw 2 waves


one with an
amplitude of 5 mm and one with an
amplitude of 2 mm


Frequency


The number of
cycles
/wavelengths/vibrations
per unit of time


-
Measured in
Hertz

(named after Heinrich
Hertz


1888


1st demonstrated the
presence of electromagnetic waves)



Represented by “f” ; f= 1/t


(Equal to vibrations per
second

(1Hz = 1 vibration/1 second)


You can hear 20 Hz to 20,000 Hz)



More
vibrations

=
shorter

amount of time for each

Remember that each wave
carries energy…


Higher frequency =
more

energy and
shorter

wavelength…The more
wavelengths per second, the more energy.

Wave
speed



how fast a wave
moves



Speed =
wavelength

/
period




(Also Notice:



Wave speed =
frequency

x
wavelength)

Draw on Notes Sheet and fill in
blanks


Wave speed depends on
medium



In a
gas
, particles are farther apart so it takes
longer for them to find each other and bump into
each other
-

sending the wave


In
liquids
, particles are
closer

together so waves
travel faster


In
solids
, particles are very
close

together so
waves travel the fastest

Discussion: (Not to write down)

Can sound waves travel in air?


Sound

waves can travel in air


However, they travel even faster in
solids

than in air or
water

Example: hitting a metal railing and listening (you will
hear two bangs)

Why?


The first sound comes through the steel rail itself and
reaches you shortly before the second sound, which
travels through the air.


Another Example: Earthquakes

(you don’t need to know
this…yet)


Produce
seismic

waves


P waves (
primary
)


travel faster, arrive first,
longitudinal waves (shake everything side
-
to
-
side)

S waves (
secondary
)


slower, carry more
energy, transverse waves (shake everything
up and down


more damage)

More practice…Draw on another
sheet


1. Draw a wave with a period of .5
seconds and a frequency of 2 Hz


2. Draw 2 waves


one with a high
frequency and one with a low
frequency:

LIGHT ENERGY

Frequency of Light Spectrum (example)




Wide range of frequencies and wavelengths


Your eyes can detect 4.3 x 1014 Hz to 7.5 x 1014 Hz (visible light
range)


Electromagnetic waves exist at frequencies we can’t see


Doppler Effect



First


pitch is determined by
frequency


Sound waves travel out from an object in wave fronts and hit
your eardrum (when they hit your eardrum, they have a
frequency equal to the number of wave fronts that hit your
ear


Ambulance example:


When the ambulance moves toward you, the sound waves are
compressed because the ambulance moves a short distance


so
the waves hit your eardrum at a higher frequency


higher pitch


Then, when the ambulance moves away from you, the distance
between the wave fronts is more than before, so the frequency is
lower


pitch is lower


Doppler effect can also happen in light and other types of
waves



http://physics.bu.edu/~duffy/semester1/c20_wave_spee
d.html



wave speed different medium


http://www.teachersdomain.org/resource/ess05.sci.ess.
watcyc.wavemotion/



surface wave


http://www.acoustics.salford.ac.uk/feschools/waves/wav
etypes.htm



transverse right angles


http://www.acoustics.salford.ac.uk/feschools/waves/refl
ect.htm#reflect



reflection