PH 105
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PH 105
Dr. Cecilia VogelLecture 3
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OUTLINE Oscillations Waves
graph sound types
Wave behavior reflection diffraction
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Properties of Oscillations Amplitude is
how far it gets from larger amplitude,
Period is the time it takes to time before
Frequency is how the _____ the period, the _____ frequently it repeats. f = 1/T
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Period and Frequency Period and frequency of a system
depend on properties of system like, ______ of spring, _____ of pendulum, ______ in string
does ____ depend on ______ for simple systems Demo:
What is the period of pendulum for small amplitude oscillations? For large amplitude? What will change the period?
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Damping Will the oscillation go on forever
all oscillations lose
Because of Damping is due to factors like
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Waves A wave is a disturbance
that carrying
A sound wave is a disturbance of (air) molecules the disturbance causes
and
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Waves A sound wave is a disturbance of
(air) molecules pressure Does a difference in pressure carry
energy? Does it have the ability to do work?
If a volume, V, of gas has pressure greater (or less) than atmospheric pressure (Po) by an amount p, then the energy is
2
2
1p
P
VPE
o
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Graphs of Waves Pressure varies with position
p
x (cm)1 2 3
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Wave Propagation
Where the pressure is low
Where the pressure is high
affects nearby regions wave
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Graphs of Waves So pressure at a particular
place also the pressure wave passes this
point at
p
t (s)1 2 3
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Impulsive Waves These are graphs of
they are not do not
For impulsive wave: Time the impulse traveling speed =
demo of wave speed. What changes it?
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Periodic Waves Waves that repeat
with a period, T or frequency, f
Time graph:
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Wavelength One cycle will travel
before the next cycle starts so the position graph
distance between repeats is called the
Position graph:
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Speed A wave travels by the time another oscillation starts,
travels distance = in time =
Tv
time
distance fv for a given material, the larger demo: vary freq, watch wavelength
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2-D and 3-D Waves Sound waves (light waves, water waves…)
from a point source travel
spherical wave
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Reflection When a wave meets an obstruction,
traveling back though
Is the wave the same after it reflects? What does an impulsive wave look like after reflecting off a fixed end?
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Reflection When a wave meets a free end,
it often reflects Why does it reflect?
Is the wave the same after it reflects?
What does an impulsive wave look like after reflecting off a free end?
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Reflection in 2-D or 3-D A wave will reflect
just like angle of incidence = demo: ball and mirror
A point source will be reflected the reflected wave
or virtual source
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Whispering Gallery A curved reflecting surface can focus sound
it sounds like it comes from
There are spots in the science bldg where you hear a voice think it’s but actually The sound was reflected and focused, making an
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Diffraction When a wave meets an obstacle
that doesn’t totally or one that
it can diffract or to get
video
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Diffraction SometimesNote that a wave will not diffract,
if its wavelength is
Ex: Visible light has wavelengths ____________ than a meter,
do not see through a doorway, or around a tree
Ex: Audible sound has wavelengths ______a meter
you can hear through doorway, or around a tree.
Ex: in lab, to see _________ without too much __________, must use ultrasound
“ultra” meaning high high freq corresponds to
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Summary
Sound is propagating disturbance of molecules,
graph pressure vs time or vs position
wave speed depends on mediumwavelength and frequencyWaves can:
reflect when meet obstruction or free spacediffract around obstacle or thru opening