WAVES: basics

Chapters 25.1-25.8; 26

Simple Harmonic Motion

The equal or balanced back and forth or side to The equal or balanced back and forth or side to side motion of a particle that is caused to side motion of a particle that is caused to vibrate by a disturbance.vibrate by a disturbance.

Similar to a pendulum’s motion.http://www.physics.uoguelph.ca/tutorials/

shm/Q.shm.html

WHAT IS A WAVE?

A repeating disturbance that causes vibrations and transmits energy through matter or space.

WHAT IS THE PURPOSE OF A WAVE?

To transmit energy from one place to another.

WHAT HAPPENS TO ENERGY AS THE WAVE

TRAVELS?Energy is transferred from one particle

to the next.The motion of particles in a medium is

like the motion of masses on a spring.Energy of the wave spreads away from

the disturbance or vibration (see white board)

IS MATTER TRANSMITTED WITH THE WAVE?

No, only energy is transmitted. The particles in the matter vibrate as the

wave passes, but do not travel with the wave.

http://www.infoline.ru/g23/5495/Physics/English/waves.htm

http://members.aol.com/nicholashl/waves/movingwaves.html

ARE THERE DIFFERENT TYPES OF WAVES?

Mechanical Waves Non-Mechanical Waves

microwavesSound waves

Mechanical WavesWaves that can only travel through

matterExamples: sound, water and seismic

waves In general, mechanical waves travel fastest

through solids, then slower through liquids and slowest through gases

Can be transverse or longitudinal (or compressional)

Non-Mechanical WavesWaves that can travel through matter

or space (a vacuum)Example: electromagnetic radiation

(waves) or lightIn general, non-mechanical waves travel

fastest through a vacuum, then slower through gases, then liquids and slowest through solids

Two perpendicular transverse waves

Electromagnetic Wave

http://www.nrc-cnrc.gc.ca/obj/inms-ienm/images/research_images/optical_comb/COMBFIG1.gif

Wave Speed

Wave speed (depends upon the composition and character of the medium it travels through)

Two types of waves based upon direction of vibrating particles: Transverse Waves cause particles

in matter to vibrate perpendicular to the direction of wave travel.

Longitudinal Waves cause particles in matter to vibrate in the same direction of wave travel.

http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html

TRANSVERSE WAVE

crest

trough

amplitude

Onewavelength

Rest position

LONGITUDINAL WAVECompression (more dense)

Rarefaction (less dense)

one wavelength

Wave Characteristics

Frequency (f) (the number of vibrations that occur in a given time)Hertz (Hz) (# of vibrations per second)High frequency waves produce waves with

short periods and short wavelengthsPeriod (P) (the time it takes for one wave cycle to

pass)Seconds (s)The lower the frequency, the longer the period

Wave CharacteristicsWavelength λ (lambda) (the distance between one point

on a wave to the next identical point; crest to crest, for example)Meters (m) The lower the frequency, the longer the wavelength

Amplitude (longitudinal waves—the tightness of the compression; transverse waves—the distance from the crest to rest position or from trough to rest position)Meters (m)The greater the amplitude of the wave, the more

energy the wave transfers.

Frequency vs. Intensity

Rate of vibration (frequency)Amount of energy (intensity)—

Amplitude (amount of displacement)loudness (relative intensity of sound)brightness (number of photons of light)

Turn up the volume--same frequencies, different intensity

Why do waves become less intense away from the source?

Same amount of energy is spread out over greater and greater distances.

Same energy at every point along a wave front.

Also, simple harmonic motion of the particles can be dampened (or absorbed or transferred) by the medium (rubber, clay, springs, fluids in shock absorbers)