Vibrations

1
Vibrations Waves

• Advanced Physics Presentation

2
Waves

• A wave is a disturbance which causes a transfer
  of energy
• Mechanical Wave need a medium in order to
  travel
• Electromagnetic Waves do not need a medium
• Waves can be transverse or longitudinal

3
Transverse Waves

• When the particles of the disturbed medium move
  perpendicularly to the wave motion.
• Example
• Waves in the stretched strings of musical
  instruments
• Waves upon the surfaces of liquids
• Radio and Light waves

4
Longitudinal Waves

• When particles move along the direction of the
  wave rather than at right angles to it.
• The medium vibrates parallel to the direction of
  the energy transfer
• Example
• Sound Waves

5
Characteristics of Waves

• Frequency
• Period
• Wavelength
• Amplitude
• Speed
• Trough
• Crest

6
Crests Troughs

• The high points of the wave are called crests
• The low points of the waves are called troughs.
• Amplitude is the distance from the mid-point to
  the crest (or trough) of the wave.

7
Wavelength

• Wavelength is described as the distance from the
  top of one crest to the top of the next one.
• It is also the distance between successive
  identical parts of the wave.

8
Frequency

• How often a vibration occurs is called the
  frequency.
• The unit of frequency is called the hertz (Hz)
• A frequency of one cycle per second is 1 hertz,
  two cycles per second is 2 hertz, and so on.

9
Frequency and Period

• If the frequency of a cycle is known then the
  period can be calculated.
• Therefore if the period is known then the
  frequency can be calculated.
• The formula is
• Frequency 1/period or Period 1/frequency

10
Question

• Using the previous formula and information answer
  the following question.
• What is the frequency in vibrations per second of
  a 100-Hz wave?
• Hint 1 cycle per second 1 Hz

11
Answer

• A 100-Hz wave vibrates 100 times per second.

12
Question

• The Sears Tower in Chicago sways back and forth
  at a frequency of about 0.1 Hz. What is its
  period of vibration?
• Hint period 1/frequency

13
Answer

• The period is 1/frequency 1vib/0.1hz
• 1vib/0.1vib/s 10s
• Each vibration takes 10 seconds

14
Wave Speed

• The speed of a wave depends on the medium through
  which it travels.
• Wave speed equals frequency times wavelength.
• Formula v?f
• Where v is wave speed ? (lambda) is wavelength
  and f is frequency.

15
Question

• If a water wave vibrates up and down two times
  each second and the distance between wave crests
  is 1.5m, what is the frequency of the wave? What
  is its wavelength? What is its speed?
• Hint v?f

16
Answer

• The frequency of the wave is 2Hz its wavelength
  is 1.5m and its wave speed is wavelength X
  frequency
• 1.5m 2Hz 3m/s

17
Question

• What is the wavelength of a 340-Hz sound wave
  when the speed of sound in air is 340m/s?

18
Answer

• The wavelength of the 340-Hz sound wave must be 1
  m.
• Then wave speed 1m 340 Hz 340m/s.