WAVES…

Definition of a WAVE…

• Waves are an oscillating disturbance propagating in space• Waves transfer

energy.

Breakdown Description of a WAVE

• Oscillation– vibration– back and forth motion of individual particles as they remain in

one location– describes the motion of matter

• Propagation– wave motion– transfer of energy through the medium or vacuum by

successive particle vibrations– describes the motion of the wave and the transfer of energy

Anatomy of a WAVE.• Crests: where the wave is highest, or at it’s

greatest disturbance.• Troughs: where the wave is the lowest, or the

disturbance is the greatest, in the opposite direction from the crest.

• Amplitude: the distance from the midpoint to the maximum (crest) of the wave.

• Wavelength: the distance from the top of the crest of a wave to the top of the following crest.

• Sine Curve: a pictorial representation of a wave.

Sine Curve

Frequency of a WAVE

• Frequency: the number of vibrations an object makes in a unit of time.- a complete back-and-forth vibration in one

cycle.- the unit of frequency is called hertz (Hz).

Speed of a WAVE• The speed of a wave depends on the medium

through which the wave moves. Example:- Sound waves moves at speeds of about 330 m/s in air, and move about four times faster in water.

• Whatever the medium, the speed, wavelength, and frequency of a wave are related.

• Calculating speed.- you can calculate the speed of a wave by

multiplying the wavelength by the frequency.

Types of WAVES…Waves come in many shapes and forms. While all waves have basic characteristics and behaviors, some have can be distinguished from others based on both observable and non-observable characteristics.

Electromagnetic & Mechanical

1. Electromagnetic WAVE…• a wave that is both electric and magnetic which carries

energy produced by the vibration of charged particles.• capable of transmitting its energy through open space.• Transverse only.• For example:

Light waves produced from the sun travel to Earth through the vacuum of outer space. Without the capability of traveling through open space, the Electromagnetic waves would never be able to reach the Earth, therefore leaving the planet dark and lifeless.

2. Mechanical WAVE…• is a wave that is not capable of transmitting its energy

through open space. • Mechanical waves require a medium (solid, liquid, or gas)

in order to transport their energy from one location to another.

• Can be transverse or longitudinal• Examples: 1. Sound wave requires air

2. Slinky waves require the coils of the slinky.3. Water waves require water.4. Stadium waves require the fans in the stands.

Types of Wave motions

Transverse – oscillations perpendicular to the direction of propagation

Longitudinal – oscillations parallel to the direction of propagation

Rarefaction

Transverse Wave Examples:1. Light waves2. X-Rays 3. Radio waves

Longitudinal Wave examples:

1. Tsunami waves2. Sound waves3. Earthquake

waves (P-waves)

Duration of a Wave…

Pulse – a short disturbance propagating in space

Basically, a pulse is a single disturbance that moves from point A to point B.

Basically, a Periodic Wave is a multiple disturbance that moves from point A to point B.

Periodic Waves – continuous periodic oscillation driven by a periodic driving force

Wavelength

Trough

Crest

Slinky lab…

Slide 19

Fig 11.50, p.407

Doppler Effect

When an object approaches, the sound it emits seems to have a higher pitch (frequency) than it really does

Slide 20

Fig 11.50, p.407

Doppler Effect

When an object recedes, the sound it emits seems to have a lower pitch (frequency) than it really does

SONIC BOOM…

Doppler Effect

a. Pitch is determined by the frequency of sound wavesb. Frequency changes when the source of the waves is moving.c. You hear a higher pitch when the source is moving toward

you.d. You hear a lower pitch when the source is moving away from

you.

Pitch is determined by the frequency of the

sound waves

Frequency changes when the source of the

waves is moving

Doppler Effect

Stationary SourceMoving Source (v < vs)

Doppler Effect: How is this Useful?

• Radar Guns– catching speeders– timing baseball pitches

• Red Shift– Edwin Hubble (1929) observed hydrogen spectra from

distant galaxies. Noticed a shift from hydrogen spectrum on earth.

– Concluded that source of light (distant galaxies) were moving away from us

– Evidence for Expanding Universe theory– Put this information in REWIND

we begin with a very small universe

Sound Properties – Sonic Boom

a. Travel faster than the speed of sound

b. Hear nothing in front of the plane

c. Depending on position, hear the boom or just the plane, behind the plane.

Doppler Effect – Sonic Boom

Moving Source (v = vs)Moving Source (v > vs)