Waves What are they? Where are they? Stone/Ebener

(Section 1-Waves & their characteristics.) Vibrations and Waves n Oar in Water n Wings of a Bee n Electrons in an Light Bulb n Water Waves n Sound Waves n Light Waves “ Wiggles in Time” “Wiggles in Space”

Vibrations and Waves n Waves transmit energy and information. n Sound and Light are both waves. n Just Vibrations of Different Kinds

There are two ways to transmit information/energy in our universe: Particle Motion and Wave Motion

VIBRATION OF A PENDULUM n What does the period (T) depend upon? n Length of the pendulum (l). n Acceleration due to gravity (g). n Period does not depend upon the bob mass.

Simple Harmonic Motion n Defined: n The simple back-and- forth vibratory motion of a swinging pendulum n Note……the source of all waves is something that vibrates…… n Examples: n Grandfather clock pendulum n Others??

Picture of a Transverse Wave Wavelength A - Amplitude A Crest Trough WAVE DESCRIPTION

- meters or feet n n Distance between adjacent crests in a transverse wave n n Distance a wave travels during one vibration n n measured in meters or feet Wavelength ( )

n Time required to make one vibration. n Time required for the wave to travel one wavelength. n No unit. Period (  )

Frequency (f) The number of vibrations per unit of time made by the vibrating source. Units -cycles/sec or hertz (Hz)

Examples of Frequency n What is the frequency of the second hand of a clock? Frequency = 1cycle/60 secPeriod = 60 sec n What is the frequency of US Presidential elections? Frequency = 1 election/4 yrsPeriod = 4 yrs

In symbolic form or

WAVE MOTION n n Energy is transported by particles or waves. A wave is a disturbance transmitted through a medium. n n Exception: Light does not require a medium. (How do you know?)

2 basic types of waves n A) Mechanical -waves that travel through a material or medium OR waves that need matter through which to travel Ex: n B) Electromagnetic- light waves OR waves caused by a disturbance in the electric & magnetic fields OR waves emitted by vibrating electric charges Ex:

How do you know it’s wave motion? Because a disturbance moves through the medium. This causes elements of the medium vibrate. Example: ripples on water Other ones?????

WAVE SPEED The average speed is defined as

For a wave, if the distance traveled is a wavelength ( ), then the time to travel this distance is the period (T). Thus or

is true for all waves. v is dictated by the medium. f is dictated by the source. ( Sound travels at 340 m/s in general…but really depends on the actual temperature.)

SSELL/DEMOS/WAVES- INTRO/WAVES-INTRO.HTML Waves Animations:

TRANSVERSE WAVES Particles vibrate perpendicular to the wave motion string musical instruments ripples on water electromagnetic waves e.g. Light waves, x-rays, radio waves

Picture of a Transverse Wave Crest Trough Wavelength A A - Amplitude

LONGITUDINAL WAVES Particles vibrate parallel to the motion of the waves Sound Waves

Rarefactions are regions of low density. Compressions (condensations) are regions of high density.  is the length of one rarefaction plus one compression

SOUND Section 2

n Did you know that….. mechanical waves displace matter to transfer energy …..and thus can be in the same place at the same time. mechanical waves displace matter to transfer energy …..and thus can be in the same place at the same time.

Interference n Interference patterns occur when 2 waves from different sources arrive at the same point-at the same time. n Examples?

n Constructive: when the crest of one wave overlaps the crest of another n Destructive: when the crest of one wave overlaps the trough of another Types of Interference

Constructive Interference: Reinforcement + Maximum In phase displacement In phase displacement

n Constructive

Destructive Interference: Exactly out of Phase Cancellation + Zero displacement

Destructive: crests & troughs overlap

Is interference is a characteristic of these waves. Sound waves? Light waves? Water waves?

Interference also called Superposition n When two waves interact, the principle of superposition says that the resulting wave sum of the two individual wave s. This phenomena interference. n

Standing Wave V V V V Incident Wave Reflected Wave

Standing Waves n Waves having fixed point s that appear not to move at all (nodes) n & moving points that appear to oscillate through the entire amplitude of the wave (antinodes) n Important in stringed instruments

n There is no vibration at a node. n n There is maximum vibration at an antinode.

Sound n Travels as a longitudinal wave n Is a mechanical wave n Sounds audible to humans range from ,000 Hz

n Frequency & Pitch: How are they related? a) As f increases, pitch also rises. b) Pitch refers to how frequency is observed. c) How is this observed in musical instruments? Examples? Examples?

Speed of Sound n speed of sound depends on medium and temperature n speed of sound in 0 ºC is 331 m/s…it increases by 0.6 m/s for every 1 ºC increase

Speed of Sound Problems (Hewitt) n 1. Sound waves travel at an average of 340 m/s. What is the wavelength of a sound with a frequency of 20 Hz? What about one with a frequency of 20 kHz? n 2. A bat flying in a cave emits a sound and receives its echo.10 seconds later. Show that the distance to the wall is 17 m. n 3. A submarine surveys the bottom of the ocean floor with ultrasonic sound that travels 1530 m/s in seawater. Find the depth of the water if the time delay of the echo to the ocean floor & back is 8 seconds.

DOPPLER EFFECT n n Refers to the change in frequency as the wave approaches. As the wave gets closer, the pitch gets higher. As the waves source moves away, the observer encounters a lower frequency.

Doppler Effect n What are some examples we see every day?

n Shock Wave The cone-shaped wave made by an object moving at supersonic speed through a fluid. (Here, the source is moving faster than the wave speed, which is the speed of sound!!) (Super-sonic speed)

SHOCK WAVES n n There are two booms, one from the front of the flying object and one from the back.

Shock Wave

n Sonic Boom The loud sound resulting from the incidence of a shock wave. (This is the result of the pile up of many wave fronts which produces a sonic boom)

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