WAVES

A method of energy transfer without the mass movement of particles.

Disturbances that travel through a medium or space

Animations courtesy of Dr. Dan Russell, Kettering University

Energy is transferred without the physical net transfer of matter.

There are two types of waves:

1) Mechanical Wave-- requires a material medium to travel through

SOUND

2) Electromagnetic Waves-- May travel through space (a vacuum) light, X-Rays, gamma rays

Mechanical waves are categorized by how they travel through the medium:

Transverse Waves the displacement of the particles of the medium is perpendicular to the propagation of the wave.

?

Breakers are waves that have “fallen over” because the medium is too shallow!

Water waves (not breakers) are examples of transverse mechanical waves.

Longitudinal Waves displacement of the particles of the medium is parallel to the propagation of the wave.

Ex: Sound wave

Longitudinal Wave Characteristics

Compression Rarefaction

Wavelength () the distance from one point in phase to the next point in phase. The length of one complete cycle.

2 Reubens tube demo

Transverse Wave Characteristics

Crest

Trough

amplitude

Period (T)the time it takes to complete a single cycle- the time for one single wavelength.

frequency (f) the number of cycles per second

• measured in Hertz (Hz): cycles per second or waves per second

f = 1/T T = 1/f

Wave speed (v) how fast the wave travels

v = f units:

Hz(m) = m/s

A tuning fork that is marked 262 Hz is struck and produces wavelengths that are measured in a lab to be 1.28 m. What is the speed of sound in this lab?

f = 262 Hz

= 1.28 m v = ?

v = f

= (262 Hz)(1.28 m)

= 335 m/s

What would the wavelength of a 128 Hz tuning fork be in the same lab?

= v/f= (335 m/s)

128 Hz= 2.62 m

Two fishing boats are positioned so that one is atop a crest while the other is at the bottom of an adjacent trough. The boats oscillate and pass each other 22 times in a minute. The boats are exactly 6.00 m apart when they pass each other. What is the speed of the waves that are oscillating the boats?f = 11waves

60 s

f = .183 Hz

= 2(6.00 m) = 12.0 m

v = f

= (.183 Hz)(12.0 m)

= 2.20 m/s

Wave Interactions

Light travels in a straight line, very un-wave like:

Move one of the boards and…

Reflection

Bouncing of a wave off of a boundary:

Hard Boundary

Soft Boundary

Refraction: Bending of waves as they change speed passing from one medium to another:

Diffraction: Waves spread through an opening--

Interference: When waves interact in such a way as to reinforce/cancel each others’ effects:

Superposition: the effects of waves on the medium they travel through:

Superposition Examples

Impedance: the resistance of the medium to passing the wave energy:

Impedance Examples

Damping: Loss of wave energy traveling through a medium

Wave Interactions

Rectilinear Propagation

Reflection

Diffraction

Refraction

Interference

Impedance

Damping

loss of energy

bouncing

spreading

bending

straight line

effects of waves

wave “friction”

Superposition waves affect medium