Physical Science Chapter 17 NOTES Mechanical Waves and SOUND (Characteristics of Waves)

Physical Physical ScienceScience

Chapter 17 NOTESChapter 17 NOTESMechanical Waves and Mechanical Waves and

SOUNDSOUND(Characteristics of Waves)(Characteristics of Waves)

What are waves?What are waves? WaveWave – when energy moves through a medium as a vibration – when energy moves through a medium as a vibration MediumMedium – the material through which a wave passes – the material through which a wave passes

Waves travel through the medium without actually moving the medium Waves travel through the medium without actually moving the medium with it.with it.

3 main types3 main types TransverseTransverse LongitudinalLongitudinal SurfaceSurface

Transverse WavesTransverse Waves Cause the medium to

vibrate at right angles to the direction the wave travels

Has a crest (top) and trough (bottom)

Draw this!!! Example – ripple on a Example – ripple on a

pondpond Transverse Wave Video

clip Wave animation

Longitudinal WavesLongitudinal Waves

move particles move particles parallel to the parallel to the direction the wave direction the wave is moving, “push-is moving, “push-pull” waves.pull” waves. Example – sound Example – sound

waves in airwaves in air Draw this!Draw this! Video clip transver

se vs. longitudinal waves

Has compression Has compression and rarefaction and rarefaction (decompression)(decompression)

Grandpa John – Wave Motion

List examples of each type of wave as you watch the video.

So, Examples of Transverse? Radio and light

Examples of Longitudinal? Sound and earthquakes

Surface Surface WavesWaves

Travel on a surface separating 2 media

object on the surface moves in circles - a combo of transverse and longitudinal wave movement

Example – ocean waves

Ocean waves animation

Ocean Waves Near Shore

Wave simulation

Properties of Waves Period (T)

Frequency (ƒ)

Wavelength (λ)

Speed (v)

Amplitude

Properties of waves video clip

Period and Frequency Period (T) - time

required to go through one cycle. Measured in seconds

Frequency (ƒ)- number of cycles in a certain time.

ƒ=1/T measured in s-1

or Hz HERTZHERTZ, one , one HzHz

Wavelength

Wavelength (λ)- distance between two identical points on consecutive waves measured in meters

(or km, cm, etc) Increasing the

frequency of a wave decreases its wavelength.

Speed

Speed (v) - how fast the wave is moving

v=λƒ measured in m/s (or km/s, cm/s, etc)

Amplitude Amplitude - max displacement from its

rest position (also known as wave height) measured in meters (or km, cm, etc) Example – dropping a pebble in the water

vs. doing a “cannonball” jump into the water

VERY IMPORTANT: The more energy a wave has, the greater is its amplitude!!!

Classwork/Homework

p. 503) 1-7 p. 507) 2, 3, 8-10 p. 527) 1-6, 13-15, 30-33

Study the Chapt 17!

Warm-up

Did you do these? p. 503) 1-7 p. 507) 2, 3, 8-10 p. 527) 1-6, 13-15, 30-33

Study your notes! You have a Quiz on Waves!!!

SpeedSpeed (meters/sec)= wavelength x frequency (meters/sec)= wavelength x frequency FrequencyFrequency (Hz = 1/sec)= speed / Wavelength (Hz = 1/sec)= speed / Wavelength WavelengthWavelength (meters) = speed / Frequency (meters) = speed / Frequency

Designated by Greek letter lambda - Designated by Greek letter lambda -

Speed Frequency & Speed Frequency & WavelengthWavelength

Speed

Wavelength x frequency

S

x f

S = x f = 1.5 m x 280 Hz = 420 m/s

= S / f = 5.0 m/s / 2.5 Hz = 2 m

Speed

Wavelength x frequency

p.506 in textbook

Interactions of WavesInteractions of Waves Reflection is when waves, whether physical or

electromagnetic, bounce from a surface back toward the source. Ex - a mirror reflects the image of the observer.

Refraction is when waves, whether physical or electromagnetic, are deflected when the waves go through a substance. The wave generally changes the angle of its general direction.

Diffraction is the bending of a wave as it moves around an obstacle or passes through a narrow opening.

Interference- when two waves Interference- when two waves collidecollide

Constructive Interference Constructive Interference – the – the combining of waves to cause higher combining of waves to cause higher amplitude of any of the original waves.amplitude of any of the original waves.

Destructive Interference Destructive Interference – when the – when the combining of the waves produce a new combining of the waves produce a new wave with a smaller amplitude than wave with a smaller amplitude than the beginning wavesthe beginning waves

Standing WavesStanding Waves appear to stay in one place

result of constructive and destructive interference between original wave and reflected wave

contains node(s) and antinode(s)

Forms only if half a wavelength or a multiple of it fits exactly into the length of the rope

Sound and Hearing17-4

Properties of Sound Waves Longitudinal waves

speed- travels at different speeds in different media

air- 343m/s fresh water- 1510m/s Salt water- 1550m/s

Aluminum- 5000m/s Intensity- rate at which a wave's energy flows

through an area measured in Decibels, dB Loudness- physical response to sound Pitch- frequency of sound as you hear it.

Higher frequency, higher note Infrasound and Ultra sound

The Doppler Effect Change in frequency due to motion

of source, listener, or both Ex: When a vehicle sounding a siren

or horn approaches, passes, and recedes from an observer.

Sonic Boom- breaking of sound barrier

Basically the object goes faster than the speed of sound

http://www.kettering.edu/~drussell/Demos/doppler/doppler.html

Sonic boom explained

Hearing and our Ears

Outer Ear- gathers and focuses sound into middle ear

Middle Ear- receives and amplifies vibrations

Inner Ear- uses nerve endings to sense vibrations

Hammer, anvil, cochlea

Instruments

alter pitch by changing frequency of standing waves

change tension, length, and amplitude

Resonance- increased amplitude over time because of added energy.

Resonance animationResonance animation

Video Clip

Sonic Boom

Sonic boom explained

Deadliest catch – monster waves

World’s Biggest Wave ever surfed

Go over QS !!

p. 503) 1-7 p. 507) 2, 3, 8-9 p. 527) 1-6, 13-15, 30-33

Wrap-up

What is the Doppler effect?

What is a sonic boom?