Ch. 14: Waves and Energy Transfer

14.1: Wave Properties

Mechanical Waves• Transverse Waves (Secondary waves or S waves):– Wave that travels perpendicular to the direction of motion– In an earthquake these arrive second

• Longitudinal Waves (Primary waves or P waves):– Wave that travels parallel or in the same direction as the

motion– In an earthquake, these arrive first

• Surface Waves (Rayleigh and Love waves):– Both travel like transverse waves but they are

perpendicular to one another– Most dangerous waves in an earthquake

Examples

• A sound wave is an example of a ________ wave.

• An ocean wave is an example of a _________ wave.

• Earthquake (seismic Wave) = ____

Measuring a Wave• Amplitude = max displacement from rest/

equilibrium

Measuring a Wave• Wavelength (λ) = distance between points where

the wave pattern repeats itself (usually in meters) – Crest to crest or trough to trough

• Speed = distance wave travels/ time V= Δd/Δt

Measuring a Wave• Period (T) = the time (in seconds) it takes for a point (p) to

return to its initial position• Frequency = the number of complete oscillations it makes

each second…– To calculate frequency (f) = 1/T = 1/ (sec) = Hz

• Both apply only to continuous waves

Measuring a Wave

• Wavelength, speed, period and frequency• Velocity (V)= m/s = Wavelength (λ) / Period (T)IF: Frequency =1/T T= 1/f Simplifying: • V = λ/T λ/ (1/f)• SO: V =λf• V=wavelength * frequency

Example Problem pg. 333

• A sound wave has a frequency of 262 Hz and a wavelength measured at 1.29 m.A) What is the speed of the wave?B) How long will it take the wave to travel the

length of a football field, 91.4 m?C) What is the period of the wave?

14.2 Wave Behavior

Waves at Boundaries

• Incident wave: wave that strikes the boundary

• Reflected wave: the returning wave– If the reflected wave is from a less dense medium

it will be reflected in the same manner– If the reflected wave is from a more dense

medium it will be inverted from its original position.

Superposition of Waves

• Principal of Superposition: The displacement of two or more waves overlapping, is the algebraic sum of the individual waves.

• Interference: the result of 2 or more waves– Destructive: waves add– Constructive: waves cancel (result = 0/ node)

Superposition of Waves• Interference: the result of 2 or more waves– Constructive: waves add– Destructive: waves cancel (result = 0/ node)

Continuous Waves

• Waves generated as a continuous train of oscillations with a constant frequency and amplitude.

Standing Waves• The combination of 2 waves of equal frequency and

intensity travelling in opposite directions.• There are usually 2 displacements: One where the

maximum amplitude occurs at the same points as other minimum value of the amplitude of the other.

Waves in Two Dimensions• Reflection– Law of reflection: the angle of incidence is equal

to the angle of reflection

Waves in Two Dimensions• Refraction– The change in direction of waves at the boundary

between two different media

Diffraction and Interference of Waves• Diffraction:– The spreading of waves around the edges of a

barrier• Ex. Around a coral barrier reef

Wave Interference