Conceptual Physics Notes on Chapter 25 Vibrations & Waves.

Conceptual PhysicsConceptual Physics

Notes on Chapter 25Notes on Chapter 25

Vibrations & WavesVibrations & Waves

Vibrations & WavesVibrations & Waves

Any “wiggle” in time is called a Any “wiggle” in time is called a

VVibrationibrationMake that “wiggle” move through Make that “wiggle” move through space, it makes a space, it makes a

WaveWave

Vibrations & WavesVibrations & Waves

The time is takes for a The time is takes for a vibration to make a back-vibration to make a back-and-forth swing is called the and-forth swing is called the PeriodPeriod of the wave. of the wave.

A A long pendulumlong pendulum has a longer has a longer period than a period than a shorter pendulumshorter pendulum; ; that is, it swings back-and -forth that is, it swings back-and -forth more slowly --- more slowly --- less frequentlyless frequently --- --- than a short pendulum.than a short pendulum.

Vibrations & WavesVibrations & Waves

To produce this “wiggle”, you can To produce this “wiggle”, you can use a spring, a pendulum, or use a spring, a pendulum, or string. Any of these will produce string. Any of these will produce

Simple harmonic motion.Simple harmonic motion.

Vibrations & WavesVibrations & Waves

Let’s look at a waveLet’s look at a wave::

A A

CC DD

BB

Vibrations & WavesVibrations & Waves

High points on the wave are called High points on the wave are called CrestsCrests..

Low points on the wave are called Low points on the wave are called TroughsTroughs..

The The WavelengthWavelength is the distance from the top is the distance from the top of one crest to the top of the next crest, or of one crest to the top of the next crest, or distance between successive identical parts distance between successive identical parts of the wave.of the wave.

AmplitudeAmplitude refers to the distance from refers to the distance from midpoint to crest (or trough) on a wave.midpoint to crest (or trough) on a wave.

Vibrations & WavesVibrations & Waves

FrequencyFrequency is how often a is how often a wave passes a given point wave passes a given point in a given time. (A complete in a given time. (A complete back-and-forth swing, or up-back-and-forth swing, or up-and down movement.)and down movement.)

Frequency is measured in Frequency is measured in cycles per secondcycles per second or or

Hertz Hertz ((HzHz).).

Vibrations & WavesVibrations & Waves

Example:Example: – 1 cycles per second is 1 Hz.1 cycles per second is 1 Hz.– 2 cycles per second is 2 Hz.2 cycles per second is 2 Hz.

Higher frequencies : kHz --- 1000 HzHigher frequencies : kHz --- 1000 Hz

MHz --- 1000000 HzMHz --- 1000000 Hz

NOTE FROM ABOVE that frequency and NOTE FROM ABOVE that frequency and period are related:period are related:

Frequency = 1 / periodFrequency = 1 / period

Period = 1 / frequencyPeriod = 1 / frequency

They are inverses of each other!They are inverses of each other!

Vibrations & WavesVibrations & Waves

Transverse WaveTransverse Wave A wave that is traveling at A wave that is traveling at right anglesright angles to the direction of travel.to the direction of travel.

““Shaking the rope up and downShaking the rope up and down””

Vibrations & WavesVibrations & Waves

Longitudinal WaveLongitudinal WaveA wave that is traveling in the A wave that is traveling in the same same directiondirection to the direction of travel. to the direction of travel.

““Push in and pull outPush in and pull out””

Vibrations & WavesVibrations & Waves

InterferenceInterference

Interference can be Interference can be

CONSTRUCTIVECONSTRUCTIVE

or or

DESTRUCTIVEDESTRUCTIVE..

Vibrations & WavesVibrations & Waves

Constructive Constructive interferenceinterference is when is when two waves two waves in phasein phase addadd to make a larger to make a larger wave.wave.

Destructive Destructive interferenceinterference is when is when two waves two waves out of out of phasephase subtractsubtract to to make a smaller wave.make a smaller wave.

Vibrations & WavesVibrations & Waves

Standing WavesStanding WavesA standing wave occurs when a wave is A standing wave occurs when a wave is reflected backreflected back toward the sourcetoward the source..

Vibrations & WavesVibrations & Waves

In a standing wave, certain parts of the rope In a standing wave, certain parts of the rope remain stationaryremain stationary --- --- NODES.NODES.

The The largest amplitudeslargest amplitudes are known as --- are known as ---ANTINODESANTINODES..

Vibrations & WavesVibrations & Waves

Doppler EffectDoppler EffectA change in frequency due to the motion of the A change in frequency due to the motion of the object or observerobject or observer..

The Doppler Effect can also be observed in light --- The Doppler Effect can also be observed in light --- blueblue or or redred shift! shift!