waves. waves are everywhere. sound waves, light waves, water waves, stadium waves, earthquake waves,...

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Waves

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Page 1: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Waves

Page 2: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Waves

• Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just a few of the examples of waves.

• Waves transport energy from one location to another.• Waves are caused by vibrations • Vibration (or oscillation) -- back-and-forth or up-and-down

motion; a wiggle in time.• Wave -- a disturbance that travels from one location to

another; a wiggle in space and time.• The medium is a substance or material that carries the wave.

Page 3: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Anatomy of a Sine Wave• The parts of a wave include crest, trough,

wavelength, amplitude, frequency and period

The points A and F are called the CRESTS of the wave.

crest

This is the point where the wave exhibits the maximum amount of positive or upwards displacement

trough

The points D and I are called the TROUGHS of the wave.These are the points where the wave exhibits its maximum negative or downward displacement.

Page 4: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Anatomy of a Sine Wave• The distance between the rest position (shown by the dashed

line) and point A is called the amplitude of the wave.• The amplitude is the maximum displacement that the wave

moves away from its equilibrium (dashed line).• The distance between two consecutive similar points (in this

case two crests) is called the wavelength.• The wavelength is also the length of the wave pulse.

Amplitude

Wavelength

Wavelength

Wavelength

Page 5: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Comparison of Characteristics of Waves

• These two waves have the same

frequency but different amplitudes. • These two waves have the same amplitude but different frequencies.

Page 6: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Frequency

• Hertz- a unit of frequency (named after Heinrich Hertz). 1 Hz = 1 vibration per second. Ex. 10 hertz means 10 vibrations per second. Radio stations operate on hertz frequencies.

• Pitch is the frequency of sound.• Our limitations of hearing- 20 Hz to 20,000 Hz.

– Ultrasonic (sound to hi frequency for us to hear)– Infrasonic (sound too low frequency for us to hear)

Page 7: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Frequency and Period• Frequency measures how often something

happens over a certain amount of time (# of waves/second). It is the number of complete waves that pass a point in a given period of time (usually a second).

• We can measure how many times a pulse passes a fixed point over a given amount of time. This will give us the frequency.

Page 8: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

The Period of a Pendulum• Period – time it takes for 1 complete wave to pass a point. Measured in sec.• The motion of a pendulum and the motion of a mass on a spring can be

described using a wave.• The period of a pendulum is the time is takes for one full back and forth

motion.

Page 9: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Frequency and Period

• The period is also is the reciprocal of the frequency.• Period = 1/ frequency T = 1 / f• Frequency = 1/ period f = 1 / T

Page 10: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Speed• Wave speed is the distance the disturbance travels in a fixed

amount of time. • Wave speed can be determined from the product of the

wavelength and the frequency• velocity = wavelength x frequency

• v = f• All waves traveling thru the same medium do so at the same

speed!

Page 11: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Factors Affecting Speed• Electromagnetic (light/radiant) waves travel at 3.0 x

108 m/s in air while sound travels in air at 3.0 x 102 m/s. 186,000 mi/s vs. 0.21 mi/s.

• Three factors that affect the speed of the wave in transferring energy are:– 1. Type of medium– 2. Temperature of medium– 3. State of matter of medium (solid, liquid, gas)

Page 12: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

WaveTypes• Waves which require a medium are

mechanical waves, also known as compressional or longitudinal waves.

• Waves which do not require a medium are transverse waves, commonly electromagnetic waves.

Page 13: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Motion• Most waves we see travel through some

substance or matter (medium), but weirdly enough, the medium doesn’t really travel just the energy.

• Examples of Mediums-1. Air2. Water3. All phases of matter (s,l,g)**Not all waves require a medium though!**

Page 14: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Types of Waves

• Transverse wave - oscillations are transverse (perpendicular) (at right angles to) to the direction of motion

• Longitudinal (or Compression) wave - oscillations are in the direction of motion, or parallel to the direction of motion.

Page 15: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Transverse Waves

• Electromagnetic waves (light waves) are transverse.

• This is the same for stringed instruments.

Page 16: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Electromagnetic Waves

Page 17: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Visible Spectrum

Page 18: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Longitudinal Waves• Also known as compressional waves or

mechanical waves• Medium compres-

ses together orspreads out to formcompressions andrarefactions

Page 19: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Longitudinal Waves

•Sound waves are longitudinal waves. They are produced by the vibrating air molecules.

Page 20: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Uses of Longitudinal Waves

Page 21: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Interference and the Superposition Principle• Suppose two waves pass through the same medium. What

happens?• Wave interference is the phenomenon which occurs when

two or more waves meet while traveling along the same medium.

• The superposition principle tells us how waves interact.• The principle of superposition is sometimes stated as follows:

When two waves interfere, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location.

Algebraic sum of two waves

Page 22: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Interference

• There are 2 types of interference: destructive and constructive.

• Destructive interference- this occurs when the crest of one wave overlaps the trough of another. This cancels the waves out.

• Constructive interference- occurs when the crests of two waves overlap causing them to join, this increases the amplitude.

Page 23: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Constructive Interference• Constructive interference is a type of interference which occurs

at any location along the medium where the two interfering waves have a displacement in the same direction. The resulting displacement is greater than the displacement of the two interfering pulses alone.

Page 24: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Destructive Interference• Destructive interference is a type of interference which

occurs at any location along the medium where the two interfering waves have a displacement in the opposite direction. The resulting displacement is less than the displacement of the two interfering pulses alone.

Page 25: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Addition

Page 26: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Interference

• Beats – periodic changes in intensity of sound• Inference in light produces light and dark

patterns

Page 27: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Two Opposite Waves• When the two opposite waves arrive at the same

location, they cancel, destructively.

Page 28: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Interference• Water waves from two oscillating sources show

interference. Note light and dark areas where difference amounts of light pass thru the water.

Ripple Tank

Page 29: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Boundary Behavior of Waves• The behavior of a wave when it reaches the end of its

medium is called the wave’s boundary behavior.• When one medium ends and another begins, that is called a

boundary.• One type of boundary that a wave may encounter is that it

may be attached to a fixed end.

The reflected pulse has the same speed, wavelength, and amplitude as the incident pulse.

Page 30: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Standing Waves• When a reflected wave interferes with an incident

wave, a standing wave can form.

Nodes are points of no motion

Anti-nodes are points of maximum motion

Page 31: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Reflection

Page 32: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Behavior• Now the we know the parts of a wave and how we

describe and analyze them, we can look at wave behavior

• In the next section we will look at interference, the boundary behavior of waves, standing waves and the Doppler Effect.

The Doppler Effect

Page 33: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

The Doppler Effect• The Doppler Effect is the apparent change in frequency of a wave due to

relative motion between source and observer.• As the sound move toward the observer, the apparent frequency

decreases, the waves get compressed.• As the sound moves away from the observer, the apparent frequency

increases, the waves get “stretched out”• A sound wave frequency change is noticed as a change in pitch.

Page 34: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Doppler Shift for

Light

Page 35: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Doppler and Line of Sight

We are only sensitive to motion between source and observerALONG the line of sight.

Page 36: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Shock Waves

• When speed of objectgenerating waves

surpasses speed of waves in thatmedium, shock waveresults

Page 37: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Shock Waves

• The more the sourceexceeds the wave speedthe narrower the V

Page 38: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Reflection

• Normal line (perpendicular to plane surface ) bisects incoming and outgoing ray to determine angle of incidence or angle of reflection

Page 39: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Reflection

• Law of reflection – angle of incidence = angle of reflection

Page 40: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Reflection

• From a single point

Page 41: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Reflection

• From a concave surface

Page 42: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Reflection

Acoustics of room design is very interesting. Need some reflections to “liven” the room. Too many reflections and the sound gets mushy. Look in a concert hall or auditorium to see the different sound treatments

Page 43: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Behavior- Refraction• Refraction- the bending of waves in various

angles as it goes from 1 medium to another.

Page 44: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Refraction

• Waves traveling from the deep end to the shallow end can be seen to refract (i.e., bend), decrease wavelength (the wavefronts get closer together), and slow down (they take a longer time to travel the same distance).

Page 45: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Refraction

Page 46: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave BehaviorDiffraction

• Diffraction -- object causes a wave to change direction and bend around it.

• The amount of bending depends on the size of the obstacle and the wavelength of the wave.

• If an obstacle is larger than the wavelength , the waves do not diffract much.

Page 47: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Natural Frequencies

• Objects have “natural” frequencies based on their size and structure

• Guitar strings are an example• Timpani heads• Air columns

Page 48: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Forced Vibrations

• Can externally impose a vibration on an object• Guitars and violins and pianos• Set the wood into motion at the frequency of

the string• This provides a larger surface to interact with

the air• Harp vs. Piano

Page 49: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Resonance

• When the forced vibration matches a natural frequency we get a “resonance” condition

• Think about a swing on a playground• You go high when you pump the swing at its

natural vibration frequency• Other examples:

– Sympathetic vibrations in tuning forks– Famous Tacoma Narrows bridge collapse

Page 50: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Resonance

Swinging a child in a playground swing is an easy job because you are helped by its natural frequency.

But can you swing it at some other frequency?

Page 51: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Opaque, Transparent, Translucent

• Wave behaviors cause objects to appear differently.

Page 52: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Reflection and Refraction

Page 53: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Harmonics• There are a variety of patterns by which the guitar

string could naturally vibrate; each pattern is associated with one of the natural frequencies of the guitar strings.

Page 54: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Sources

• Conceptual Physics by Paul Hewitt• www.physicsclassroom.com• pls.atu.edu/physci/physics/people/robertson/courses/

phsc1013/PHSC1013-Waves.ppt –• Waves and Vibrations -Physics: Mr. Maloney• www.drake.edu/artsci/physics/Lecture_14_3-4-2004.ppt• https://bba-physics.wikispaces.com/file/view/Waves2.ppt• www.knott.k12.ky.us/schools/teachers/nritchie/waves

%20good%20copy.ppt

Page 55: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Characteristics of ALL waves!• Crest

(compression)• Trough

(Rarefactions)• Wavelength• Amplitude• Frequency• Wave Speed- V=f

Page 56: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Sound in warm air near the ground doesn’t seem to carry well because the warm air causes the sound to bend away from the ground. This is just the opposite for cool air.

Page 57: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

Wave Questions1) Rhonda sends a pulse along a rope. How does the position of a point on

the rope, before the pulse comes, compare to the position after the pulse has passed?

2) Why don't incoming ocean waves bring more water on to the shore until the beach is completely submerged?

3) In order for a medium to be able to support a wave, the particles in the wave must bea) frictionless.b) isolated from one another. c) able to interact. d) very light.

4) A transverse wave is transporting energy from east to west. How will the particles of the medium will move?

5) A wave is transporting energy from left to right. The particles of the medium are moving back and forth in a leftward and rightward direction. This type of wave is known as a _______________.

Page 58: Waves. Waves are everywhere. Sound waves, light waves, water waves, stadium waves, earthquake waves, waves on a string, and slinky waves and are just

More Wave Questions

6) In the diagram above, the wavelength is given by what letter?7) In the diagram above, the amplitude is given by what letter?8) A wave has an amplitude of 2 cm and a frequency of 12 Hz, and the

distance from a crest to the nearest trough is measured to be 5 cm. Determine the period of such a wave.

9) A tennis coach paces back and forth along the sideline 10 times in 2 minutes. The frequency of her pacing is ________.

10) A pendulum makes 40 vibrations in 20 seconds. Calculate its period?11) Mac and Tosh are resting on top of the water near the end of the pool

when Mac creates a surface wave. The wave travels the length of the pool and back in 25 seconds. The pool is 25 meters long. Determine the speed of the wave.

12) A marine weather station reports waves along the shore that are 2 meters high, 8 meters long, and reach the station 8 seconds apart. Determine the frequency and the speed of these waves.