Wave Lecture(narrows bridge: http://www.youtube.com/watch?

v=xox9BVSu7Ok)wave lecture intro: (http://www.youtube.com/watch?

v=jAXx0018QCc)bill nye: waves

(http://www.youtube.com/watch?v=OGyRe_SGnck)

1. Wave properties

A. waves are the transfer of kinetic energy through a medium or vacuum:

-sound though air,

-light through space: vacuum

-heat through a metal pan: solid

B. when waves travel through matter:

1. it transfers kinetic energy

2. but medium/matter remains in place:

-grass blades waving in the wind,

-sound through walls

- ocean waves

3. the energy in motion carries information: sound, pictures and numbers

matter remains in place: net circular motion

C. waves have a repeating cycle (back-and- forth), called an oscillator,

-like a person on a swing (pendulum) or

-a vibrating string on a guitar

1. repeating motion is also called harmonic:

heartbeat,

solar seasons,

singing in

harmony

Harmonic wave motion

2. one full revolution is called a cycle,

known as one unit of harmonic motion

3. waves move around a point of equilibrium: where the system is at “rest”, with a net force of zero

D. energy/inertia pulls the wave away from equilibrium and the restoring force brings the wave back to the point of equilibrium:

= restoring force

= equilibrium

Demo Newton’s cradle:Newton’s first law

E. wave part/labels

1. crest: top of the wave

2. trough: bottom of the wave

3. equilibrium: half way between crest and trough

F. wavelength: distance from crest to crest,

(or trough to trough)

- Greek symbol lambda, = upside down y:

G. amplitude: size of a wave (cycle)

1. wave height from point of equilibrium to top of crest (or half wave height from

trough to crest)

2. amplitude will reduce (dampen) toward equilibrium with less wave energy

-direct relationship

H. frequency: how often vibrations (wave cycles) occur

1. number waves per time:

-usually the number of wave crests per second

2. unit is the Hertz (Hz) = # waves

second

low frequency

high frequency

I. radio waves:

-AM radio: alters amplitude of waves (height)

-FM radio: alters frequency of waves (how often)

J. period: amount of time for a cycle: crest to crest (how much time for a class period?)

K. frequency and period are inverse relationships:

period = 1

frequency

frequency = 1

period

L. wave speed

1. within same medium = same speed

2. different densities of matter cause different wave speeds:

more dense =

more inertia =

slower wave speed

- an inverse relationship

3. greater the elasticity of the medium (ability to bounce back to original position), the faster the wave speed

- ie: steel faster than air: tap on a steel wall vs talking through air

- direct relationship

4. wave speed =

-distance/time or

-frequency x wavelength =

(# waves/sec x distance crest to crest)

2. Wave types

A. transverse waves (sine waves)

1. medium motion (oscillation) is perpendicular to the wave motion (up/down)

- as a water wave moves toward the shore, the crests/troughs move up

and down

-examples of transverse waves:

light, heat, ocean/water, earthquake, Tacoma Narrows bridge

B. longitudinal waves

1. medium motion in same direction (parallel) as wave motion (oscillation)

2. waves of alternating regions of matter crowded together (compressions)

and matter spread apart: rarefactions

3. sound waves are longitudinal waves

3. Wave interactions

- when energy waves move they are influenced by the boundaries they collide with and influence other waves they run into

A. reflection (as in a mirror image)

- wave/energy is not absorbed but bounced, how much depends the surfaces’ degree of absorption

- example: mirrors, barrier reefs, sound walls

- incoming wave angle (incident wave) =

outgoing wave angle (reflected)

reflected wave: incident = reflected

reflected waves: wavelength and frequency remain unchanged, usually (if energy is not absorbed)

B. refraction

- bending of wave due to a change in speed- due to changing one medium to another

medium, thus changing density of the medium

-pencil in water:

- how would a pencil in oil look?

light refraction from air to glass mediums (what album cover?):

C. diffraction

-waves bending around or through an obstacle: sound traveling around a corner

-waves passing through a hole: changes to circular waves

diffraction waves: circular waves produced: explains why sound can be heard through small opening.

D. absorption

-waves can get smaller as they transfer energy into the medium they travel through:

ie: light passing through sunglasses, sound passing through sound boards in a recording studio

E. wave to wave interference

- when two or more waves collide at the same point in space and time

1. constructive

a. wave crests meet and combine

b. form a single wave

c. amplitude is increased: additive of two original waves

d. resonance

- when the natural frequency of an object matches the input wave frequency

- causes a dramatic increase of energy and thus an increase in amplitude of the generated wave:

-musical instruments

-Tacoma narrows bridge

-Calvary troops across marching across a footbridge in Manchester,England (1831)

constructive interference

2. destructive

a.when the crest of one wave meets the trough of a second wave

b. forms a single wave

c. amplitude is decreased: energy is subtracted

d. ie: anti-noise technology for earphones

and so, the sun’s waves set yet again at the ocean waves, groovy!