Waves and Sound
(Chapter 25-26)
I
can
de(ine
and
use
the
terms
period,
wavelength,
frequency,
amplitude,
Hertz,
crest,
trough,
transverse,
longitudinal,
and
standing
waves.
Waves and Sound
(Chapter 25-26)
A wave is "energy on the move."
slinky & cup demo
A wave is "energy on the move."
In an ocean wave, does the water move forward?
A wave is "energy on the move."
In an ocean wave, does the water move forward?
Waves move up and down! (If all the water moved forward
eventually all the ocean would wind up on the beach....)
A wave is "energy on the move."
A wave is "energy on the move."
crest
trough
A wave is "energy on the move."
crest
one wavelength
trough
A wave is "energy on the move."
crest
one wavelength
trough
A wave is "energy on the move."
crest
one wavelength
trough
amplitude
A wave is "energy on the move."
crest
one wavelength
trough
amplitude
A wave is "energy on the move."
crest
one wavelength
trough
node
amplitude
Wave Vocab:
Crest - high points of wave
Trough - low points of wave
Amplitude - distance from midpoint to crest (or trough)
Wavelength (λ) - The distance for the wave to complete on full cycle (crest to crest, etc.)
Frequency (f) - number of vibrations per unit of time.
Wave Vocab:
Crest - high points of wave
Trough - low points of wave
Amplitude - distance from midpoint to crest (or trough)
Wavelength (λ) - The distance for the wave to complete on full cycle (crest to crest, etc.)
Frequency (f) - number of vibrations per unit of time. Units - Hertz (Hz)
frequency =
1
time period (s)
Hertz = s-1
Wave Speed
The speed of a wave depends on the medium through which it travels.
(water, air, rock, etc.)
Wave Speed
The speed of a wave depends on the medium through which it travels.
(water, air, rock, etc.)
velocity = λf
Wave Speed
The speed of a wave depends on the medium through which it travels.
(water, air, rock, etc.)
velocity = λf
If a water wave vibrates up and down two times each second and the
distance between wave crests is 1.5 m, what is the frequency of the
wave?
What is the wavelength?
What is the speed?
Wave Speed
The speed of a wave depends on the medium through which it travels.
(water, air, rock, etc.)
velocity = λf
If a water wave vibrates up and down two times each second and the
distance between wave crests is 1.5 m, what is the frequency of the
wave?
What is the wavelength?
What is the speed?
f = 1/2 sec = 0.5 Hz
λ=1.5 m
v = 0.75 m/s
Wave Speed
* Sounds is a wave--Higher frequencies are higher
pitches!
Frequency, Amplitude, or Wavelength??
a
The human ear can detect nearly 20 000 sound vibrations each second.
b
The distance between two successive compressions of a sound wave
can be about 0.35 metres.
c
In the 1970s, rock group ʻThe Whoʼ played the loudest ever rock concert.
d
In one second, three water waves passed my boat!
e
The decibel scale can be used to measure loudness.
f
Pavarotti sings with a very low voice.
Frequency, Amplitude, or Wavelength??
a
The human ear can detect nearly 20 000 sound vibrations each second.
frequency
b
The distance between two successive compressions of a sound wave
wavelength
can be about 0.35 metres.
c
In the 1970s, rock group ʻThe Whoʼ played the loudest ever rock concert.
amplitude
d
In one second, three water waves passed my boat!
frequency
e
The decibel scale can be used to measure loudness.
amplitude
f
Pavarotti sings with a very low voice.
wavelength
Frequency, Amplitude, or Wavelength??
1. The frequency of a guitar string is 440 Hz. What does this mean?
2. The vertical distance from the trough of a water wave at sea to its crest
is 6.8 m. What is the amplitude of the wave?
3. A boy notices that 450 complete waves travel past him in one and a half
minutes. What is the frequency of the source that produces these water
waves?
Frequency, Amplitude, or Wavelength??
1. The frequency of a guitar string is 440 Hz. What does this mean?
Every second, 440 sound waves are created. The period is 0.0023 seconds.
2. The vertical distance from the trough of a water wave at sea to its crest
is 6.8 m. What is the amplitude of the wave?
6.8/2 = 3.4 meters
3. A boy notices that 450 complete waves travel past him in one and a half
minutes. What is the frequency of the source that produces these water
waves?
f = 450 / 90 sec = 5 Hz
Types of Waves
Types of Waves
Transverse Waves - motion is perpendicular to direction of wave oscillation
(light, musical strings, radio waves)
Longitudinal Waves - motion is parallel to direction of wave oscillation
(sound)
Interference
Grab a partner and go to a computer to do the
interference simulation!
Interference
a.
b.
c.
d.