mechanical waves. physics olympics

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