WAVES

Mr. Banks

8th Grade Science

WAVES

• A wave is a disturbance that transfers, or carries energy from one place to another.

• Classified by what they move through

• For mechanical Waves energy is transferred by vibrations of a medium (medium = matter, stuff)ex/ ocean waves move through water

• For electromagnetic waves (EM Waves)energy moves through disturbances in the electromagnetic field.

WAVE STRUCTURE

CREST (peak)

AMPLITUDE

WAVELENGTH

TROUGH

WAVE STRUCTURE

• Wavelength – the distance

between the same point

in two waves.

• Amplitude – the distance

from the middle of the

wave to the maximum crest

or trough.

• Frequency – The number of

waves that pass a specific

point each second.

MECHANICAL WAVES

• Mechanical waves are

waves that require a

medium to transmit their

energy.

• Travel through & gradually

lose energy to that medium.

Examples:

• water, sound, rope, & spring

waves

Mechanical wave media:

• water, air, rope, spring

MECHANICAL WAVES

Longitudinal

transverse

surface

TRANSVERSE WAVES

• Examples:

• Guitar strings

• Electromagnetic waves(ex: light)

• Particle vibration is perpendicular

(sideways or up and down) to the

direction of the motion of the wave

LONGITUDINAL WAVES

• Also called compression or pressure wave.

• Instead if crests and troughs, there are alternating

areas of compression and rarefaction.

• Examples:

• Sound waves

• P-type earthquake waves

Particle vibration is parallel to the direction

of the motion of the wave (back and forth).

Rarefraction (expansion)

Compression

SURFACE WAVES

• Particle vibration is in a circular

motion.

• Occur at the boundary between

two different mediums.

• Particles move more the closer

they are to the surface.

• Example:

• Ocean waves

AMPLITUDE• Distance between the “middle & crest” or

“middle & trough”

• The amplitude is directly related to the “power”

of a wave

• Does not affect the velocity of a wave

• Determines strength (earthquake), loudness

(sound), or brightness (electromagnetic wave)

WAVELENGTH

• Distance between any two repeating points on a wave

• crest-crest, trough-trough,rarefraction-rarefraction, compression-compression

WAVELENGTH

• For waves moving at the same speed, Shorter wavelengths have a higher frequency because the waves aren’t as long

WAVELENGTH

• Determines

• What colors we see.

• What sounds we hear (pitch). Shorter wavelengths are higher pitched.

Frequency ƒ

• The number of waves that pass a specific point

each second.

• measured in Hertz (Hz) = number of wavelengths

passing a spot in 1 second.

VELOCITY v• the rate (speed) at which

the wave travels.

• Wave speed depends on

medium.

• Mechanical waves

travel faster through

dense mediums.

• EM Waves are faster

through less dense

mediums (space)

Calculating wave velocity

1. What is the wavelength of a water wave if

its frequency is 4 Hz and its velocity is 12

m/s?

2. Calculate the velocity of a wave if the

frequency is 54 Hz and the wavelength is

25 m.

3. Calculate the velocity of a wave if the

frequency is 120 Hz and the wavelength is

65 m.

4. What is the wavelength of a water wave if

its frequency is 33 Hz and its velocity is 7

m/s?

5. What is the wavelength of a water wave if

its frequency is 7.5 Hz and the wave speed

is 53 m/s?

Which is a longitudinal wave, and

which is a transverse wave?

Wave reflectionReflection occurs when waves change

directions as a result of "bouncing off" a

surface like a mirror.

Wave refractionThe bending of a wave when it enters a

medium where its speed is changed.

• Different temperatures of air allow

waves to travel at different speeds.

• This means that they cause refraction.

• Extreme differences in temperature (like

in the desert) can cause light waves to

bend and make mirages.

Wave diffractionA change in the direction of a wave as

it passes through an opening or around

an object in its path.

Wave interferenceTwo waves can interact with one

another, this interaction is called

interference.

Constructive Destructive

Wave interference

Copyright © 2010 Ryan P. Murphy

• Waves can be absorbed by objects and

converted into other types of energy.

• For example, light waves can be

absorbed by objects and are usually

converted into heat. However, if they

strike a solar panel that light can be

converted into electricity.