Waves

1
Waves
25.2-25.4
2
Review

• What is frequency?
• How often a vibration occurs
• What are the units of measurement called?
• Hertz (Hz) vibrations (cycles) per second

• Period

• The time it takes to complete one cycle

Which wave has a high frequency? Low?
3
Objectives

1. Characteristics and properties of waves
2. Describe wave motion
3. Calculate wave speed

4
Simple Harmonic Motion(SHM)

• What is it?
• The back and forth motion
• i.e. pendulum or mass on spring
• Creates a sine curve
• Draw a basic sine curve

5
Wave Components
crest
trough

• Crest
• the high point of wave
• Trough
• the low point of wave
• Amplitude
• distance from midpoint to crest of wave
• Wavelength
• distance between successive identical parts of
  the wave

6
Wave Motion

• Waves transfer energy NOT matter
• i.e., leaf in a pond moves up and down, but not
  along with the wave buoys surfers
• Energy transferred is carried by disturbance in
  the medium
• Annimation

7
Wave Speed

• Wave speed depends on medium
• i.e. 350m/s air, 1400m/s water
• How do you determine wave speed?
• Fixed spot, distance between crests (wavelength),
  count of crests passing per second.

8
The Equation

• Wavespeed wavelength x frequency
• v ? f
• Lets try. . .
• The wavelength of an ocean wave is 4 meters and
  one crest passes by a pier each second. What is
  the wavespeed?
• 4m x 1 per sec 4m/s
• Using the same wave, what if TWO crests pass by
  the pier each second? Whats the wavespeed?
• 4m x 2 per sec 8m/s

9
At a Concert

• High frequency guitar solo
• Draw on board
• Low frequency bass guitar
• Draw on board
• Which one do you hear first?
• Neither! Travel at the same speed.

10
Practice Question

• If a water wave vibrates up and down two times
  each second and the distance between crests is
  1.5 m, what is the wave speed?
• Frequency is 2 Hz wavelength is 1.5m wave speed
  is 1.5m x 2 Hz 3m/s