5A_2 – Slide 1
Topic 5A:
Waves, Part II
Online Lecture:
Wave Characteristics
Describing Waves: Crests & Troughs
5A_2 – Slide 2
○ Crests (high points) & Troughs (low points)
Water
WaterLevel
Level(feet)
(feet)
Snapshot of Waves (i.e., waves at a single instant in time):
44
Crest
Wavelength
33
Crest
Height
Trough
Trough
22
1
1
0
0
Crest
10
10
20
20
30
40
30
40
Horizontal Distance (feet)
Horizontal Distance (feet)
Trough
50
50
60
60
70
70
Describing Waves: Height & Wavelength
5A_2 – Slide 3
○ Wavelength = horizontal distance between crests
– how deep the wave orbitals “reach:”
“Wave Base” = 1/2 wavelength
○ Height = vertical distance from trough to crest
– size of the wave orbitals
Water Level (feet)
4
Wavelength
3
Height
2
1
0
10
20
30
40
Horizontal Distance (feet)
50
60
70
Summary: Orbitals, Height, and Wavelength
Wavelength
½ Wavelength
A
5A_2 – Slide 4
Height
B
Wave Base
No Motion
Describing Waves: Steepness
○ Wave Steepness =
5A_2 – Slide 5
Height
Wavelength
– If the steepness
becomes greater
than 1/7th (=0.14),
Height
the wave
breaks
S te
epn
ess
Wavelength
If the slope is too steep, molecules start to slide.
Maximum Height of Waves
5A_2 – Slide 6
Which wave can have a larger height without breaking,
a long- or short-wavelength wave? Why?
Ste
Height
epn
e ss
Wavelength
S te
Height
ep n
e ss
Wavelength
5A_2 – Slide 7
Describing Waves: Time
“1 wave every
10 seconds”
○ period = time “between” wave crests
how long until the next wave crest passes by
(e.g., a period of time)
“6 waves per minute”
○ frequency = how many waves pass by in a certain amount
of time, how "often" waves pass by
– Period and Frequency are opposites :
A long-period wave has a low frequency,
and a high-frequency wave has a short period.
Important: Period/Frequency do not change,
even as waves approach a beach.
Measuring Period & Frequency
Begins here.
How could you
measure the
wave period
at the beach?
frequency?
5A_2 – Slide 8
Begins here.
5A_2 – Slide 9
Deep
Tank
Shallow
Tank
Wave Speed
(in Shallow Water)
Describing Waves: Speed
5A_2 – Slide 10
○ Do waves move faster in shallow water or deep water?
Deep Water
○ If a wave can "feel the bottom,"
its speed depends on how deep the water is:
the deeper the water, the faster the wave
– Why do waves move slower in shallow water?
Orbitals
“touch”
the
bottom.
If a wave cannot “feel the bottom,”
its wavelength controls its speed
(longer wavelength = faster).
A long-wavelength wave
typically has a long period.