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VIBRATION AND WAVES Sound and Light

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VIBRATION AND WAVES Sound and Light Pendulum Pendulum s Period: The time required for one complete vibration, for example, from one crest to the next crest, is ... – PowerPoint PPT presentation

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Title: VIBRATION AND WAVES Sound and Light


1
VIBRATION AND WAVES Sound and Light
2
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3
Pendulum
4
Pendulums Period
  • The time required for one complete vibration, for
    example, from one crest to the next crest, is
    called the pendulum's period and is measured in
    seconds. The formula to calculate this quantity is

5
The formula to calculate this quantity is
  • where
  • L is the length of the pendulum in meters
  • g is the gravitational field strength, or
    acceleration due to gravity

6
FREQUENCY
  • The frequency of a pendulum represents the number
    of vibrations per second. This quantity is
    measured in hertz (hz) and is the reciprocal of
    the pendulum's period.   

7
EXAMPLE 1
  • What Would Be the Period of a Pendulum Located at
    Sea Level If It Is 1.5 Meters Long?

8
Solution 1
  • 2.46 seconds
  •  

9
EXAMPLE 2
  • If the pendulum's length were to be shortened to
    one-fourth its original value, what would be its
    new period?

10
SOLUTION 2
  • 1.23 Seconds

11
EXAMPLE 3
  • At sea level, how long would a pendulum be if it
    has a frequency of 2 Hz?

12
SOLUTION 3
  • 6.21 cm

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14
EXAMPLE 4
  • The Sears Building in Chicago sways back and
    forth at a frequency of 0.1 Hz.
  • What is the period of its vibration?

15
EXAMPLE 4
  • The period is 1/frequency.
  • 1 vib / 0.1 Hz 1 vib/0.1vib/sec
  • 10 sec.

16
TYPES OF WAVES
  • Transverse Wave
  • Longitudinal Wave

17
Longitudinal Wave wave particles vibrate back
and forth along the path that the wave
travels. Compressional Wave
18
Transverse waves wave particles vibrate in an
up-and-down motion.
19
Longitudinal Wave
20
Transverse Wave
http//www.phy.ntnu.edu.tw/ntnujava/index.php?topi
c14.0
21
Wave Speed
22
Wave Speed
  • Speed Wavelength Frequency

23
Example 5
  • 4. A ruby-throated hummingbird beats its wings at
    a rate of about 70 wing beats per second.
  • What is the frequency in Hertz of the sound wave?
  • b. Assuming the sound wave moves with a velocity
    of 350 m/s, what is the wavelength of the wave?

24
Solution 5
  • f 70 Hz and
  • wavelength 5.0 m

25
Example 6
  • Ocean waves are observed to travel along the
    water surface during a developing storm. A Coast
    Guard weather station observes that there is a
    vertical distance from high point to low point of
    4.6 meters and a horizontal distance of 8.6
    meters between adjacent crests. The waves splash
    into the station once every 6.2 seconds.
    Determine the frequency and the speed of these
    waves.

26
Solution 6
  • The wavelength is 8.6 meters and the period is
    6.2 seconds.
  • The frequency can be determined from the period.
    If T 6.2 s, then
  • f 1 /T 1 / (6.2 s)
  • f 0.161 Hz

27
Solution 6 Contd
  • Now find speed using the
  • v f wavelength equation.
  • v f wavelength
  • (0.161 Hz) (8.6 m)
  • v 1.4 m/s

28
Example 7
  • Two boats are anchored 4 meters apart. They bob
    up and down, returning to the same up position
    every 3 seconds. When one is up the other is
    down. There are never any wave crests between the
    boats. Calculate the speed of the waves.

29
Solution 7
The wavelength must be 8 meters The period is 3
seconds so the frequency is 1 / T or 0.333
Hz. Now use speed f wavelength Substituting
and solving for v, you will get 2.67 m/s.
30
Wave Interference
  • Constructive
  • And
  • Destructive

31
Constructive Wave Interference
  • When the crest of one wave passes through, or is
    superpositioned upon, the crest of another wave,
    we say that the waves constructively interfere.
  • Constructive interference also occurs when the
    trough of one wave is superpositioned upon the
    trough of another wave.

http//id.mind.net/zona/mstm/physics/waves/interf
erence/constructiveInterference/InterferenceExplan
ation2.html
32
Destructive Wave Interference
  • When the crest of one wave passes through, or is
    superpositioned upon, the trough of another wave,
    we say that the waves destructively interfere.
  • During destructive interference, since the
    positive amplitudes from one crest are added to
    the negative amplitudes from the other trough,
    this addition can look like a subtraction.

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35
Doppler Effect
  • Some Examples

http//www.wfu.edu/physics/demolabs/demos/3/3b/3B4
0xx.html
http//www.walter-fendt.de/ph11e/dopplereff.htm
36
Doppler Effect
  • When a source of waves and an observer of waves
    are getting closer together, the observer of the
    waves sees a frequency for the waves that is
    higher than the emitted frequency.

37
Conventional Radar
All weather radars send out radio waves from an
antenna. Objects in the air, such as raindrops,
snow crystals, hailstones or even insects and
dust, scatter or reflect some of the radio waves
back to the antenna. All weather radars,
including Doppler, electronically convert the
reflected radio waves into pictures showing the
location and intensity of precipitation.
38
Doppler Radar
Doppler radars also measure the frequency change
in returning radio waves.
39
Doppler Effect Wave
Barrier Wave
Barrier (2D) Shock (3D) Wave
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