Waves - PowerPoint PPT Presentation

Loading...

PPT – Waves PowerPoint presentation | free to view - id: 77bf3b-OGZkM



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Waves

Description:

Electric Potential - Wappingers Central School District ... Waves – PowerPoint PPT presentation

Number of Views:118
Avg rating:3.0/5.0
Slides: 27
Provided by: Charl568
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Waves


1
Waves
2
Periodic Motion
  • We are surrounded by oscillations motions that
    repeat themselves
  • Understanding periodic motion is essential for
    the study of waves, sound, alternating electric
    currents, light, etc.
  • How many of you play an instrument?
  • An object in periodic motion experiences
    restoring forces that bring it back toward an
    equilibrium position
  • Those same forces cause the object to overshoot
    the equilibrium position
  • Think of a block oscillating on a spring or a
    pendulum swinging back and forth past its
    equilibrium position Demonstrate

3
Definitions of a Waves
  • A wave is a traveling disturbance that carries
    energy through space and matter without
    transferring mass.
  • Transverse Wave A wave in which the disturbance
    occurs perpendicular to the direction of travel
    (Light).
  • Longitudinal Wave A wave in which the
    disturbance occurs parallel to the line of travel
    of the wave (Sound).
  • Surface Wave A wave that has charact-eristics of
    both transverse and longitudinal waves (Ocean
    Waves).
  • Wave types

4
How does a wave vary in position and velocity?
- Full body Demonstrate - PVA graphs
5
Types of Waves
  • Mechanical Waves Require a material medium such
    as air, water, steel of a spring or the fabric of
    a rope.
  • Electromagnetic Waves Light and radio waves that
    can travel in the absence of a medium.

Medium the material through which the wave
travels.
6
Wave Motion
  • The wave is another basic model used to describe
    the physical world (the particle is another
    example)
  • Any wave is characterized as some sort of
    disturbance that travels away from its source
  • In many cases, waves are result of oscillations
  • For example, sound waves produced by vibrating
    string
  • For now, we will concentrate on mechanical waves
    traveling through a material medium
  • For example water, sound, seismic waves
  • The wave is the propagation of the disturbance
    they do not carry the medium with it
  • Electromagnetic waves do not require a medium
  • All waves carry momentum and energy

7
Types of Waves
  • In solids, both transverse and longitudinal waves
    can exist
  • Transverse waves result from shear disturbance
  • Longitudinal waves result from compressional
    disturbance
  • Only longitudinal waves propagate in fluids (they
    can be compressed but do not sustain shear
    stresses)
  • Transverse waves can travel along surface of
    liquid, though (due to gravity or surface
    tension)
  • Sound waves are longitudinal
  • Each small volume of air vibrates back and forth
    along direction of travel of the wave
  • Earthquakes generate both longitudinal (48 km/s
    P waves) and transverse (25 km/s S waves)
    seismic waves
  • Also surface waves which have both components

8
Transverse Wave Characteristics
  • Crest The high point of a wave.
  • Trough The low point of a wave.
  • Amplitude Maximum displacement from its position
    of equilibrium (undisturbed position).

John Wiley Sons
9
Transverse Wave Characteristics (cont.)
  • Frequency(f) The number of oscillations the wave
    makes in one second (Hertz
    1/seconds).
  • Wavelength(?) The minimum distance at which the
    wave repeats the same pattern ( 1 cycle).
    Measured in meters.
  • Velocity (v) speed of the wave (m/s).
  • v f?
  • Period (T) Time it takes for the wave to
    complete one cycle (seconds).
  • T 1/f

10
The Inverse Relationshipsv f?
  • The speed of a wave is determined by the medium
    in which it travels.
  • Since velocity is constant for a given medium,
    the frequency and wavelength must be inversely
    proportional.
  • As one increases, the other decreases

11
The Inverse RelationshipsT 1/f
  • Similar to the inverse relationship for frequency
    and wavelength, a similar relationship exists for
    frequency and the period.

12
Waves at Fixed Boundaries
  • A wave incident upon a fixed boundary will have
    its energy reflected back in the opposite
    direction. Note that the wave pulse is inverted
    after reflecting off the boundary.
  • Example of Waves at Fixed Boundaries

Start Per 5/6 here
www.electron4.phys.utk.edu
13
Interference
  • Interference occurs whenever two waves occupy the
    same space at the same time.
  • Law of Linear Superposition When two or more
    waves are present at the same time at the same
    place, the resultant disturbance is equal to the
    sum of the disturbances from the individual waves.

14
Constructive Wave Interference
www.electron4.phys.utk.edu
15
Destructive Wave Interference
16
Standing Waves
  • Standing Wave An interference pattern resulting
    from two or more waves moving in opposite
    directions with the same frequency and amplitude
    such that they develop a consistent repeating
    pattern of constructive and destructive
    interference.
  • Node The part of a standing wave where
    interference is destructive at all times (180o
    out of phase) .
  • Antinode The part of the wave where interference
    is maximized constructively.
  • Standing Wave

17
Continuous Waves
  • When a wave impacts a boundary, some of the
    energy is reflected, while some passes through.
  • The wave that passes through is called a
    transmitted wave.
  • A wave that is transmitted through a boundary
    will lose some of its energy.
  • Electromagnetic radiation will both slow down and
    have a shorter wavelength when going into a
    denser media.
  • Sound will increase in speed when transitioning
    into a denser media.
  • Speed of Light in different mediums

18
Continuous Waves Higher Speed to Lower Speed
  • Note the differences in wavelength and amplitude
    between of the wave in the two different mediums

Incident Reflected Wave
Transmitted Wave
Displacement
Lower speed Shorter wavelength
Higher speed Longer wavelength
Note This phenomena is seen with light traveling
from air to water.
19
Waves at Boundaries
  • Examples of Waves at Boundaries
  • Wave Types (Cutnell Johnson)
  • Waves - Colorado.edu
  • Other Examples

20
Key Ideas
  • Waves transfer energy without transferring
    matter.
  • Longitudinal waves like that of sound require a
    medium.
  • Transverse waves such as electro-magnetic
    radiation do not require a medium.
  • In transverse waves, displacement is
    perpendicular to the direction of the wave while
    in longitudinal waves, the displacement is in the
    same direction.

21
Key Ideas
  • Waves travel at different speeds in different
    mediums.
  • Light slows down when going from air to a liquid
    or solid.
  • Sound speeds up when going from air to a liquid
    or solid.
  • Waves can interfere with one another resulting in
    constructive or destructive interference.

22
Continuous Waves Lower Speed to Higher Speed
  • Note the differences in wavelength and amplitude
    between of the wave in the two different mediums

23
Review of Springs
  • Classic example of periodic motion
  • Spring exerts restoring force on block
  • k spring constant (a measure of
    spring stiffness)
  • Slinky has k 1 N/m auto
    suspensions have k 105 N/m
  • Movie of vertical spring
  • Elastic potential energy stored in spring
  • Uel 0 when x 0 (spring relaxed)
  • Uel is gt 0 always
  • We do not have freedom to pick where x 0
  • Uel conserves mechanical energy

(Hookes Law)
24
Shock Absorbers
  • Shock absorbers provide a
    damping of the oscillations
  • A piston moves through a viscous
    fluid like oil
  • The piston has holes in it, which
    creates a (reduced) viscous
    force on the piston, regardless of the direction
    it moves (up or down)
  • Viscous force reduces amplitude of oscillations
    smoothly after car hits bump in road
  • When oil leaks out of the shock absorber, the
    damping is insufficient to prevent oscillations
  • Shock absorber is example of an
    underdamped oscillator (see also
    critically damped and overdamped)

25
Properties of Waves
  • Superposition principle The overlap of 2 or more
    waves (having small amplitude) results in a wave
    that is a point-by-point summation of each
    individual wave

(constructive interference)
(destructive interference)
26
Properties of Waves
  • Traveling waves can both reflect and transmit
    across a boundary between 2 media
  • Reflected wave pulse is inverted (not inverted)
    if wave reaches a boundary that is fixed (free to
    move)
About PowerShow.com