mechanical waves. physics olympics
TRANSCRIPT
MECHANICAL
WAVES
PHYSICS OLYMPICS
http://www.gravitykills.net/PhysicsOlympics/PhysicsOlympics.htm
1. Safety! 2. Care & use
of slinkys.
SLINKY PRE-LAB:
Wave Definition:
What’s the function of a wave?
Types of Waves
#1. ELECTROMAGNETIC - NO medium required - travel @ speed of
light ex: light, radio waves,
xrays, etc
#2. MECHANICAL• How are these
waves produced?• What is the
relationship between direction of propagation and displacement of the medium?
•#2. MECHANICAL * requires a
MEDIUM (solid, liq,gas)
• ex: water, sound, spring, etc.
“ TRANSVERSE ”
(solids) disturbance is perpendicular to the direction wave travels
TYPES of MECHANICAL
DISTURBANCE MOTION
• 1. “ TRANSVERSE ”
(solids)• particles vibrate at right angles to direction wave moves
4 TypeMECHANICAL Waves
•2. “LONGITUDINAL” (solid,liquid,gas)
• disturbance is parallel to direction wave moves
4 Types of MECHANICAL Waves
DISTURBANCE
MOTION
“ LONGITUDINAL ” (solid,liquid,gas)
“push or pull”
4 Types of MECHANICAL Waves
PULSE – a single disturbance that travels through a medium
How is a pulse different than a wave ???
CREST – the high point of each wave
TROUGH – the low point of each wave
PERIOD – shortest time interval during which motion repeats itself
AMPLITUDE – the point of maximum displacement from rest or equilibruimHow does amplitude affect wave speed?
trough trough
crestamplitude
amplitude
crest
wavelength
wavelength
WAVE SPEED What affects the
rate at which a wave travels ????
v = f
= wavelength= wavelength
WAVE LENGTH How does
wavelength affect the wave
speed????
FREQUENCY How does
frequency affect the wave
speed????
MEDIUM (media)
How does medium affect
the wave speed????
EXAMPLE #1What is the period &
frequency of the threehands of the clock?
EXAMPLE #2
A wave traveling in the x-direction with a frequency of 25 Hz is shown above. Find amplitude, wavelength, period & wave speed for this wave.
A sound wave traveling at 343 m/s is emitted by the foghorn of a tugboat. An echo is heard 2.60 s later. How far away is the reflecting object?
EXAMPLE #3
A student drops a rock down a deep mineshaft. How deep is the mineshaft if he hears the rock hit the bottom 6.5 s after dropping it from rest?
EXAMPLE #4
WAVE GRILLPRE-LAB:
1. Safety! 2. Care & use of wave grills.
Law of Superposition
•waves pass through each other unchanged
•amplitudes may be added/subtracted
•result is called...
AA
CONSTRUCTIVEinterference
• waves ADD amplitudes when they meet
• displacements are on SAME
sides• point of maximum
displacement “ANTINODE” (add)
aa bb
a + ba + b
CONSTRUCTIVEinterference
waves then pass through each other
unchanged
Website simulation click here
•displacements are on opposite sides
•waves SUBTRACT amplitudes when they meet
•point of no disturbance is “NODE”
DESTRUCTIVEinterference
NN
aabb
a - ba - b
aabb
FIXED-END REFLECTION
What happens to the medium at the boundary?
FREE-END REFLECTION
What happens to the medium at the boundary?
SPEED OF SOUND PRE-LAB
“ECHO”:
“ECHO”
“ECHO”
“ECHO”
“ECHO”
SPEED OF SOUND POST-LAB: “ECHO”
1. Explain the reflection of the pulses.
2. How is the speed of sound calculated?
:
1 m
INTRO TO SOUND PRE-LAB
:
THE SOUND OF
MUSIC
•longitudinal (parallel)
•velocity depends on medium, temp, elasticity, density, etc.
•sound in air at 200C = 344m/s
(speed of light =
300,000,000m/s)
•Waves travel
slowest in gases
Pitch vs. frequency
Amplitude vs. Energy
Harmonics vs. Sound Quality
*Draw a longitudinal wave & identify areas of
compression & rarefaction
:
•Resonance (Demonstrate with resonance
boxes or speakers)
–prolonging a sound by reflection
“fundamental
frequency”
Beat 2 waves with slightly different frequencies interfere (throbbing)
(Demonstrate with resonance boxes or speakers)
Example #5:
•Four beats per second are heard when a 256 Hz tuning fork is sounded with a second fork. What are the possible frequencies of the second fork?
:
SPEED OF SOUND PRE-LAB
“RESONANCE”:
SPEED OF SOUND POST-LAB
“RESONANCE”:
Example #6:
•An open vertical tube is filled with water & a tuning fork vibrates over its mouth. As the water level is lowered in the tube, resonance is heard when the water level has dropped 17cm and again after 49 cm of distance exist from the water to the top of the tube. What is the frequency of the tuning fork?
•Define normal line•Write the geometric relationship line
•wave hits boundary & bounces out
•angle of incidence EQUALS angle of reflection * * *
•always measure from NORMAL line
barrie
r
angle ofincidence
•wave hits boundary & bounces out
•angle of incidence EQUALS angle of reflection * * *
•always measure from NORMAL line
barrie
r
angle ofincidence
angle ofreflection
•“checker- board”
barrie
r
normal
angle ofreflection
angle ofincidence
•Describe what happens to each of the following properties:–Wave speed–Wavelength –Frequency
•bending of a wave due to a change in medium (ex: air to H20)
deep
shallow
•Wave changes direction && speed at the boundary
deep
shallow
deep
shallow
•Ex: deep to shallow
• wavelength & vel. decr, but frequency stays the same!
•How does the slit opening and frequency affect the wave pattern?
•bending of waves around the edge of a barrier
•forms circular waves that spread
•smaller = smaller diffraction
•How does the source
separation & frequency affect the
wave pattern?
INTERFERENCE
•What effect does motion
have on wave speed,
wavelength & frequency?
DOPPLER EFFECT
DOPPLER EFFECT
change in due to change in position of source