Transcript Chapter 25 Notes: Waves and Vibration Vibration Wave

Chapter 25 Notes: Waves
and Vibration
Vibration: Wiggle in time.
Wave: Wiggle in space and time that extends from
one place to another.
http://staff.esuhsd.org/~dimasd/ap_physics/physics%20songs/8%
20-%20Wave%20Motion.mp3
Vibration of a Pendulum
Pendulum: Stone suspended at the end
of a string.
-Used in clocks.
Period: The time of a back and forth
swing.
The period depends on the length of the
pendulum and the acceleration of
gravity.
Long pendulum = longer period (swings
back & forth less frequently than a
short pendulum)
25.2 Wave Description
• Simple Harmonic Motion: Back
and Forth motion of a swinging
pendulum.
• Sine Curve: Curve whose shape
represents the crests and
troughs of a wave.
• Crests: High points
• Troughs: Low points
• Amplitude: Maximum
Displacement
• Wavelength: Distance from the
top of one crest to the next
crest.
• Home Position: Midpoint of
Vibration
Wave Description
• Frequency: The number of back and forth vibrations in a
given time.
• Cycle: A complete back and forth vibration.
• Hertz (Hz): Unit of frequency. 1 Hz = 1 cycle per sec. 2
Hz = 2 cycles per sec.
• Kilohertz = Thousands of hertz. (AM radio waves)
-A station at 960 KHz on the AM radio broadcasts radio
waves with a frequency of 960,000 vibrations/second.
• Megahertz = Millions of hertz (FM radio waves)
• Gigahertz = Billions of hertz. (Radar & microwave ovens)
Source of all waves is something that vibrates.
The frequency of vibrating source = frequency of wave
produced.
Frequency = 1/Period
Period = 1/Frequency
Wave Motion
Most of the information
around us travels in waves!
Sound = Energy that travels
in waves to our ears.
Light = Energy that travels to
our eyes as electromagnetic
waves.
Energy transferred from a
vibrating source to a receiver
is carried by a disturbance!
Wave Speed
The speed of the wave
depends on the medium
the wave travels through!
For example: Sound
waves travel at 330 m/s
in air and 4 times faster
through water.
Wave Speed =
Wavelength x Frequency
Transverse Waves Verses
Longitudinal Waves
• Transverse Waves: Motion of medium is at right
angles to the direction in which the wave travels.
(Musical instruments, radio and light waves, waves
on liquid)
• Longitudinal Waves: When particles move along
the direction of the wave. (Sound Waves)
Interference
• Interference Pattern: Pattern formed by overlapping
of 2 or more waves that arrive in a region at the same
time.
• Constructive Interference: Crest of one wave overlaps
the crest of another wave = a wave of  amplitude.
• (In Phase)
• Destructive Interference: Crest of one wave overlaps
trough of another wave = cancellation of waves.
• (Out of Phase)
Standing Waves
• Standing Wave: Wave in which
parts (nodes) appear stationary
and wave seems not to move.
Standing waves are the result of
interference! 2 waves of equal
amplitude and wavelength pass
in opposite directions.
• Antinodes: Positions on a
standing wave with the largest
amplitude. (1/2 way between
nodes)
Doppler Effect
Doppler Effect: The change in
frequency of a wave due to the
motion of the source or of the
receiver.
The Doppler Effect on Sound &
Light Waves
-As car passes, pitch of horn sounds
higher due to increase in sound waves.
-As car moves away, pitch drops due to
less frequency of sound waves.
-When light approaches, there is an
increase in frequency and when it
recedes, there is a decrease in
frequency.
Blue shift: Increase in freq.
Red shift: Decrease in freq.
Bow Waves
Bow Wave: The Vshaped wave produced
by an object moving on a
liquid surface faster
than the wave speed.
stationary wave source
wave source moving to the
right at a speed less than the
wave speed
wave source moving to the right at
a speed in excess of the wave
speed
wave source moving to the right at
a speed equal to the wave speed
The bow wave generated
by a speedboat knifing
through the water is
produced by the
overlapping of wave
crests.
Shock Waves
Shock Wave: Wave
produced by overlapping
spheres that form a
cone.
Sonic Boom: The sharp
crack heard when the
shock wave that sweeps
behind a supersonic
aircraft reaches the
listener.