Unit 4 Waves

Ch. 20 Sec. 1 & 2 The Nature of Waves & Properties of Waves

Waves

We often associate waves with bodies of water, but are there other situations where waves can exist?

Waves

•

wave

- a rhythmic disturbance that carries energy matter

without

carrying – matter can move the energy (pass it along), but the matter

does not move with

the energy

Types of Waves

Mechanical Waves

•

mechanical waves

- use matter to transfer energy – produced by the transfer of energy from molecule to molecule – the matter the waves travel through is called the

medium

Electromagnetic Waves

•

electromagnetic waves

do not

use matter to transfer energy – produced by moving electrically charged particles – can travel in space/vacuum (no medium needed) -

Mechanical Waves Electromagnetic Waves

Types of Mechanical Waves

Transverse Waves

•

transverse waves

- matter in the medium moves at

right angles

to the direction the wave travels – high points are

crests

& low points are

troughs

– ex. water waves

Compressional Waves

•

compressional waves

matter in the medium moves in the

same

direction as the wave travels – no crests or troughs – ex. sound waves

Compressional MW vs. Transverse MW

COMPRESSIONAL MECHANICAL WAVE TRANSVERSE MECHANICAL WAVE

IN SUMMARY…

WAVES

Mechanical Waves (medium needed) Electromagnetic Waves (no medium needed) Transverse (right angle) Compressional (same direction)

Amplitude

•

in transverse waves…

–

amplitude

- ½ the distance b/w a crest & a trough •

in compressional waves…

–

amplitude

wave - varies within a • amplitude is related to the energy of a wave

(higher amplitude = more energy)

– bright light & loud sounds have higher amplitudes

Wavelength

•

in transverse waves…

–

wavelength

distance from one crest to the next ( - the

or one trough to the next

) •

in compressional waves…

–

wavelength

the distance from one compression to the next (

or one rarefaction to the next

)

Frequency

•

frequency

- # of wavelengths that pass a certain point in 1 sec.

–

unit

=

hertz

(Hz) [wavelengths per second] • as wavelength ↑, frequency ↓ (assuming speed is equal) –

inverse relationship

• wavelength/frequency determines the color of light & the pitch of sound –

low frequency = low pitch

Wave Speed

•

mechanical waves

where , such as sound, travel faster in mediums

atoms are closer together

–

travel faster in solids, slower in liquids, & slowest in gases

•

electromagnetic waves

where , such as light, travel faster in mediums

atoms are farther apart

–

travel faster in gases, slower in liquids, & slowest in solids

• light travels much faster through air than sound –

light

travels at

300 million m/s

–

sound

travels at

340 m/s