Physics 11

Vibrations and Waves

Mr. Jean

December 15th, 2014

The plan:

Video Clip of the dayVideo Clip of the dayhttp://http://www.youtube.com/watch?vwww.youtube.com/watch?v==

WMPMzhglGooWMPMzhglGoo Introduction to waves Introduction to waves Ways to transmit & transfer energyWays to transmit & transfer energy Wave interferenceWave interference

There are two ways to transmit information/energy in our universe:

1) Particle Motion

2) Wave Motion

Light and Sound

Both are vibrations of energy and they share some similar wave properties.

Simple Harmonic Motion:

Any motion that repeats itself precisely Any motion that repeats itself precisely over equal periods of time when generated over equal periods of time when generated by a linear restoring force in accordance to by a linear restoring force in accordance to Hooke’s LawHooke’s Law. .

Piston Example:

2. WAVE DESCRIPTION

Frequency ( f ) is the number of vibrations per

unit of time made by the vibrating source.

Units - cycles per second

1/s

Hertz (Hz)

Picture of a Transverse Wave

CrestCrest

TroughTrough

WavelengthWavelength

AA

A - AmplitudeA - Amplitude

Distance between adjacent crests in a

transverse wave.

Distance a wave travels during one vibration.

in meters

Wavelength ()

The period (T) of a vibration is the time

required to make one vibration.

The The period (T) of a wave is the time (T) of a wave is the time

required to generate one wave. required to generate one wave.

It is also the time required for the wave to It is also the time required for the wave to

travel one wavelength. travel one wavelength.

FrequencyFrequency PeriodPeriod

ionsec/vibrat21

ionsec/vibrat31

ionsec/vibrat41

ionsec/vibrat2

ionsec/vibrat1

/secvibrations3

secvibration/1

/secvibrations4

ecsvibration21 /

/secvibrations2

FrequencyPeriod

1

In symbolic form

T 1foror

T1f

Example Question: A mass suspended from the end of a spring A mass suspended from the end of a spring

vibrates up and down 24 times in 36 vibrates up and down 24 times in 36 seconds. What is the frequency and period seconds. What is the frequency and period of the vibration? of the vibration?

Example Question: A mass suspended from the end of a spring A mass suspended from the end of a spring

vibrates up and down 24 times in 36 vibrates up and down 24 times in 36 seconds. What is the frequency and period seconds. What is the frequency and period of the vibration? of the vibration?

Wave Characteristics:

http://www.brightstorm.com/scienchttp://www.brightstorm.com/science/physics/vibration-and-waves/wave/physics/vibration-and-waves/wave-characteristics/e-characteristics/

3. WAVE MOTION

Energy is transported by particles or waves.

A wave is a disturbance transmitted through

a medium.

Exception: light does not require a medium.

4. WAVE SPEED

The average speed is defined asThe average speed is defined as

time

distancev

For a wave, if the distance traveled is a For a wave, if the distance traveled is a

wavelengthwavelength ( (), then the time to travel this ), then the time to travel this

distance is the distance is the periodperiod (T). Then (T). Then

Tv

fv oror

is true for all waves.

Note: v is dictated by the medium.

(must change medium to change v)

f is dictated by the source.

(must change the source to change f )

Demo - Complete Bell Wave MachineDemo - Complete Bell Wave Machine

fv

5. TRANSVERSE WAVES

Demonstration: Transverse WavesDemonstration: Transverse Waves

Examples: string musical instruments

ripples on water

electromagnetic waves

6. LONGITUDINAL WAVES

Video - Slinky Longitudinal WavesVideo - Slinky Longitudinal Waves

Parameters

Rarefactions are regions of low density.

Compressions (condensations) are regions of high density.

is the distance between successive rarefactions or successive compressions.

7. INTERFERENCE

Video - Superposition of WavesVideo - Superposition of Waves

SlideSlide - Interference - Interference

Constructive interference occurs when waves are in phase, that is when crests are superimposed and troughs are superimposed.

Destructive interference occurs when waves are out of phase, that is when crests are superimposed with troughs.

Interference is a characteristic of all waves.

Demonstrations with Audacity

Standing Waves

When two sets of waves of equal amplitude and wavelength pass through each other in opposite directions, it is possible to create an interference pattern that looks like a wave that is “standing still.” It is a changing interference pattern.

Demo - Rope and strobeDemo - Rope and strobe Demo - Mechanical overhead modelDemo - Mechanical overhead model

There is no vibration at a node. There is maximum vibration at an antinode. is twice the distance between successive

nodes or successive antinodes.