waves

Question 1

what is a wave?

Answer 1

a disturbance of the surface of water

Question 2

what are the two forces that are involved in waves?

Answer 2

generating/disturbing force & restoring force (gravity/surface tension)

Question 3

describe the wave anatomy?

Answer 3

Crest = top of the wave

Trough = bottom of the wave

Height (H) = vertical distance from trough to crest

Amplitude (α) = 1/2 height

Wavelength (L or λ) = horizontal distance crest to crest, or trough to
trough

Steepness = H / L

Question 4

speed

Answer 4

Speed (celerity!) = wavelength / period = L/T

Question 5

wave frequency

Answer 5

the number of wave crests passing point A each second

Question 6

wave period

Answer 6

the time required for the wave crest at point A to reach point B

Question 7

what’s wave motion?

Answer 7

a flow of ENERGY where particles, like a water molecule, travel in an orbital motion

Wave train indicates direction of energy movement

Question 8

explain the depth effect

Answer 8

If the bottom is deeper than ½ L
(wavelength), then circular orbits = deep
water waves

If bottom is not deeper than ½ L, then
the orbits become ellipses (flattened
circles) = shallow water waves

Friction and compression of orbits
decreases forward speed of the wave

Wave speed decreases as depth
decreases

Question 9

breaking waves

Answer 9

Wave height increases in shallow water

Bottom part of the wave moves more slowly than the top
of the wave (crest) 🡪 wave breaks

Wave breaks at critical steepness (H:L) > 1:7

Question 10

what factors influence waves?

Answer 10

Depth of water – ✔

Wind speed & duration – the greater the wind speed and the duration, the larger the waves
- Beaufort scale

Fetch – the distance the wind can blow across the water unobstructed; The greater the fetch, the greater the wave potential

For wind generated waves, fetch is key to size – a longer fetch creates a higher energy wave

Question 11

enumerate the types of waves

Answer 11

swells, standing waves (seiches), rogue waves, internal waves, tsunamis

Question 12

describe the swells

Answer 12

waves that are no longer under the influence of the wind

The waves in a fully developed sea outrun the storm that creates them, lengthening and reducing in height in the process

Swells organize into groups smooth and regular in appearance

Able to travel 1000’s of km unchanged in height and period

Question 13

describe the standing waves (seiches)

Answer 13

result from the combination of reflected waves interfering constructively with incident waves, they stay in one place instead of progressing, repeated crests/troughs in one place

e.g. at Race Rocks when the wind and tidal current are in opposition creates standing waves

Question 14

describe the rogue waves

Answer 14

Larger than expected waves, usually associated with long period waves from distant storms (also called episodic waves, sneaker waves, extreme storm waves)

Question 15

describe the internal waves

Answer 15

Waves that oscillate within rather than at

the surface, often found in stratified water at pycnoclines

Question 16

describe the tsunamis

Answer 16

generated by underwater subsidence earthquakes, landslides, meteorites, volcanoes, calving glaciers

Very long period, very fast and very large amplitude
In open ocean, a wave may be less than 1 m high, period of 10-30 minutes, wavelength of 100-200 km

At a coast, the wave may be 100 m high, with shorter wavelengths as the energy is compressed into a smaller column of water

Largest wave ever: 524 m tsunami in Lituya Bay, Alaska (1958)

Question 17

how are tsunamis detected?

Answer 17

DART: Deep-ocean Assessment and Reporting of Tsunamis

Bottom pressure recorder + surface buoy

National Buoy Data Centre

Question 18

WAVE TANK

Answer 18

Challenge: create standing waves

Oscillating water column