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PPT – VIBRATION AND WAVES Sound and Light PowerPoint presentation | free to download - id: 7a38a4-MTlmM

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VIBRATION AND WAVES Sound and Light

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Pendulum

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

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

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.

EXAMPLE 1

- What Would Be the Period of a Pendulum Located at

Sea Level If It Is 1.5 Meters Long?

Solution 1

- 2.46 seconds

EXAMPLE 2

- If the pendulum's length were to be shortened to

one-fourth its original value, what would be its

new period?

SOLUTION 2

- 1.23 Seconds

EXAMPLE 3

- At sea level, how long would a pendulum be if it

has a frequency of 2 Hz?

SOLUTION 3

- 6.21 cm

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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?

EXAMPLE 4

- The period is 1/frequency.
- 1 vib / 0.1 Hz 1 vib/0.1vib/sec
- 10 sec.

TYPES OF WAVES

- Transverse Wave
- Longitudinal Wave

Longitudinal Wave wave particles vibrate back

and forth along the path that the wave

travels. Compressional Wave

Transverse waves wave particles vibrate in an

up-and-down motion.

Longitudinal Wave

Transverse Wave

http//www.phy.ntnu.edu.tw/ntnujava/index.php?topi

c14.0

Wave Speed

Wave Speed

- Speed Wavelength Frequency

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?

Solution 5

- f 70 Hz and
- wavelength 5.0 m

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.

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

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

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.

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.

Wave Interference

- Constructive
- And
- Destructive

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

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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Doppler Effect

- Some Examples

http//www.wfu.edu/physics/demolabs/demos/3/3b/3B4

0xx.html

http//www.walter-fendt.de/ph11e/dopplereff.htm

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.

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.

Doppler Radar

Doppler radars also measure the frequency change

in returning radio waves.

Doppler Effect Wave

Barrier Wave

Barrier (2D) Shock (3D) Wave

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