Properties of WavesChapter 12 Section 3

What Is A Wave?

• Ripple waves in water are formed by the vibrations of water molecules.

• As the vibration waves spread outward to more molecules, the waves travel outward.

• A wave is considered to be the motion of disturbance.– Particles within the wave vibrate around and

equilibrium position.

Medium• Medium – Material through which a

disturbance travels.• In order for a wave to form, it needs a

medium which provides the particles that vibrate.– The medium does not travel with the wave– After the wave passes, the particles return to

their equilibrium position.• Examples:

– Sound: The medium is air– Ocean Waves: The medium is water

Mechanical Waves

• Mechanical Waves – A wave whose propagation requires the existence of a medium.

• Not all wave propagation requires a medium– Electromagnetic waves

Wave Types

• Pulse Wave – A single non-periodic disturbance.– A wave that consist of a single traveling pulse.

• Periodic Wave – A wave whose source is some form of periodic Motion.– A wave that consist of multiple traveling

pulses.

Sine Waves

• If the source of the wave is in simple harmonic motion, then the wave mimics harmonic motion as well.

• A wave that is vibrating in simple harmonic motion is called a sine wave.

– A graph of a trigonometric function produces this curve when plotted.• y = sin x

Transverse Wave• Transverse Wave – A wave whose

particles vibrate perpendicular to the direction of wave motion.– The particles vibrate up and down as the

wave moves from left to right or vise versa.• Examples:

– Electromagnetic waves– Ocean waves– Wave traveling through a rope

Graphing

• Waveform – A waveform can represent either the displacements of each point of the wave at a single moment in time or the displacements of a single particle as time passes.– Trigonometric function of sine represents the

wave.

Graphing

• The x-axis represents the equilibrium position of the wave.

• The y-axis of the curve represents the displacement of each point on the wave at time (t).

Describing a Wave• Crest – The highest point above the

equilibrium position.• Trough – The lowest point below the

equilibrium position.• Wavelength – The distance between two

adjacent similar points of the wave, such as crest to crest or trough to trough.– Variable for wavelength – λ (Greek letter – Lamda)

• Amplitude – The point at which the displacement is its maximum distance away from the equilibrium position.

Transverse Wave Diagram

Amplitude

Amplitude

Trough

Crest

Wave Length

λ

Equilibrium Position

y

x

Dis

plac

emen

t

Longitudinal Waves• Longitudinal Waves – A wave whose

particles vibrate parallel to the direction of wave motion.– The particles vibrate in the same direction as

the direction of the wave.• Often called density waves or pressure

waves– Crest are high density– Trough are low density

• Examples:– Sound Waves– Earthquakes

Longitudinal Wave Diagram

trough

crest

Compression

Longitudinal Wave

Stretched

D

ensi

ty

Equilibrium

Transverse Waves vs. Longitudinal Waves

• Transverse waves oscillate perpendicular to the direction of the wave propagation.– Light Waves

• Longitudinal waves oscillate parallel to the direction of the wave propagation.– Sound Waves

Link:• Transverse and Longitudinal Wave Animation

Period and Frequency

• Frequency describes the number of crest or troughs that pass a given point in a unit of time.

• Period of a wave is the amount of time required for one complete vibration of particles or one wavelength.

Speed of a Wave

• The speed of a wave can be found through the waves frequency and wavelength.

• The equation is derived through the linear kinematic equation for velocity.

Speed of a Wave Equation

• The speed of a mechanical wave remains constant for any given medium.

• If the frequency increases, the wavelength must decrease.

• Speed only changes if the medium changes.

Example Problem

• A 2640 Hz whistle produces sound waves that have a wavelength of 50.0 cm in water. What is the speed of sound in the water?

Example Problem Answer

• v = 1320 m/s

Energy and Waves• The energy is transferred by the motion of

the matter rather than by transferring matter itself.– Energy is transferred very efficiently in a

wave. – Examples:

• Tsunamis• Sound• Earthquake

• Greater the amplitude, greater the energy