Chapter 20: The Energy of Waves

Animation courtesy of Dr. Dan Russell, Kettering University

What is a wave? (Besides at a ballgame…lol)

Any disturbance that transmits energy through matter or spaceWhere are they?

a. in the oceanb. microwave ovensc. light waves from the sund. sound wavese. radio waves

What do waves carry?

ENERGY!!!Waves do not move particles.

Some waves need help to travel…

A medium is a substance through which a wave can travel.A medium can be a solid, liquid, or gas.What waves need a medium?

a. soundb. ocean waves

What are these waves called that require a medium? Mechanical WaveWaves that do not require a medium are called electromagnetic waves.

How waves travel:

Transverse: particles move up and down perpendicular to direction of the waveLongitudinal Waves (also called Compressional Waves): particles vibrate back and forth along the path of the wave travelsSurface Waves: combination of transverse and longitudinal waves

Section 2:Properties of Waves

B. Transverse Waves

Wave Anatomy

crests

troughswavelength

wavelength

amplitude

amplitude

corresponds to the amount of energy carried by the wave

nodes

C. Longitudinal Waves

Wave Anatomy

rarefaction

compression

wavelength

wavelength

Amount of compression corresponds to amount of energy AMPLITUDE.

Longitudinal Wave

Compression- dense regions- like the crest of a transverse wave

Rarefaction- less dense regions- like the trough of a transverse wave

Properties of Waves

Amplitude: maximum wave height from the rest position; larger amplitude = more energyWavelength: distance between crest to crest or trough to trough; compression to compression or rarefaction to rarefaction

Waves

The more energy a wave carries, the greater its amplitude High amplitude in compressional waves means

that medium is pushed together more at the compressions

High amplitude in transverse waves means taller crests and deeper troughs

http://www.sfu.ca/sonic-studio/handbook/Amplitude.html

http://id.mind.net/~zona/mstm/physics/waves/introduction/introductionWaves.html

Waves

The amplitude of compressional waves is related to how tightly the medium is pushed together at compressionDenser compressions = larger amplitude = more energyLess dense rarefactions = lower amplitude = LESS energy

Properties of Waves…

Frequency: the number of waves produced in a given amount of time; measured in hertz (Hz); 1 Hz = 1 wave per second (1 Hz = 1/s); higher frequency means higher energy

Period: the time it takes for a complete vibration

D. Measuring Waves

Velocity ( v ) speed of a wave as it moves forward depends on wave type and medium

v = × f

v: velocity (m/s)

:wavelength (m)

f: frequency (Hz)

WORK:v = × f

v = (3.2 m)(0.60 Hz)

v = 1.92 m/s

D. Measuring Waves

EX: Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz.

GIVEN:

v = ?

= 3.2 m

f = 0.60 Hz

v

f

WORK: f = v ÷

f = (5000 m/s) ÷ (417 m)

f = 12 Hz

D. Measuring WavesEX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency?

GIVEN:

= 417 m

v = 5000 m/s

f = ?

v

f

WavesLight waves travel faster in gases and vacuums than in liquids and solids Radiation moves faster when particles

are not in the way

Why are some earthquakes very damaging and other barely felt? Depends on the energy of the wave.

Waves

Amplitude of transverse wavesDistance from crest or trough of a wave to the rest position of the mediumHigher ocean waves = more energy!

Breaking a glass with sound- resonance: http://www.teachersdomain.org/resources/lsps07/sci/phys/energy/glassbreak/index.html Sound from sand dunes: http://www.teachersdomain.org/resources/hew06/sci/phys/maf/boomsand/index.htmlLight as particles: http://www.teachersdomain.org/resources/phy03/sci/phys/fund/uncertainty/index.html

Wave Interactions

Wave Interactions… Reflection

Reflection: occurs when a wave bounces back after striking a barrierAll waves can be reflected.Reflected sound waves are called echoes.Sunlight is being reflected off of the moon at night.Water waves reflect off a shoreline.

More wave interactions…

Refraction is the bending of a wave as it passes at an angle from one medium to another. Speed of refraction depends on the medium.

Wave interactions…

Diffraction: the bending of waves around or through an opening; diffraction depends on wavelength and the size of barrier/opening

Last wave interaction…

Interference: the result of 2 or more waves overlapping.a. constructive interference: increases the amplitude of a waveb. destructive interference: decreases the amplitude of a wave

Great diagram of waveshttp://www.sciencejoywagon.com/

physicszone/09waves/

More on interference waves

Can create standing wavesStanding wave is a wave that forms a stationary pattern in which portions of the wave are at the rest position.Standing waves have nodes and antinodes.

Standing Waves

Interference Waves can be deadly!

July 1, 1940- Tacoma Bridge Accident

Universal_Newsreel_Welcomes_Telenews_to_Tacoma__Tacoma_Bridge_Catastrophe.asf