Essential Questions How are waves produced? What are the types of waves? What are the consequences /

impacts of waves?

How are waves produced?

What are waves?

• Ocean waves are surface waves that occur on the free surface of oceans, seas, lakes, rivers, and canals or even on small puddles and ponds

• Ocean surface waves are also called wind waves

• Wind waves are mechanical waves that propagate along the interface between water and air; the restoring force is provided by gravity, and so they are often referred to as surface gravity waves

Wave Formation• As the wind blows, pressure and friction forces

perturb the equilibrium of the water surface. These forces transfer energy from the air to the water, forming waves

• Five factors influence the formation of waves:– Wind speed – Distance of open water that the wind has blown over (called

the fetch) – Width of area affected by fetch – Time duration the wind has blown over a given area – Water depth

• In the case of monochromatic linear plane waves in deep water, particles near the surface move in circular paths, making wind waves a combination of longitudinal (back and forth) and transverse (up and down) wave motions.

Transverse and Longitudinal Waves• Transverse

• The medium oscillates perpendicular to the wave direction.

• In the ocean, the wave moves toward the shore and the water moves up and down.

• Longitudinal• The medium

oscillates parallel to the wave direction.

Wave MotionMotion of a particle in a wind wave:

A = At deep water. The orbital motion of fluid particles decreases rapidly with increasing depth below the surface.B = At shallow water (sea floor is now at B). The elliptical movement of a fluid particle flattens with decreasing depth.1 = Propagation direction.2 = Wave crest.3 = Wave trough.

Parts of a Wave

• Crest - is the point on a wave with the maximum value or upward displacement within a cycle

• Trough - is the minimum or lowest point on a wave within a cycle

Measurements of Waves• Waves are characterized by:

– Wave height – from trough to crest – Wavelength – from crest to crest, or

from trough to trough. Measured in wavelengths (lambda -λ)

– Period – time interval between arrival of consecutive crests at a stationary point. Measures in seconds.

– Wave frequency – the number of waves passing through a point in a second.

– Wave propagation – the direction of the wave.

What are the Types of Waves

Types of Waves

• There are 3 types of waves– Capillary waves / ripples– Seas– Swells

Capillary Waves / Ripple• Ripples appear on smooth water

when the wind blows, but will die quickly if the wind stops.

• The restoring force that allows them to propagate is surface tension

• The wavelength of capillary waves is typically less than a few centimeters.

Seas

• Seas are the larger-scale, often irregular motions that form under sustained winds.

• They tend to last much longer, even after the wind has died, and the restoring force that allows them to persist is gravity

• Referred to as choppy waters• Usually have pointed crests and

rounded troughs

Swells

• Swells consist of wind generated waves that are not — or hardly — affected by the local wind at the same moment.

• Swells are often created by storms thousands of nautical miles away from the beach where they break. This distance allows the waves comprising the swells to become more stable, clean, and free of chop as they travel toward the coast .– Hurricanes in the Carribean produce very long swells

that can reach Nova Scotia a week before the storm.• Crests and troughs are rounded• Swells are not very noticeable in deeper water –

but break on shore with a large crash

Rogue Waves

• Individual "rogue waves" (also called "freak waves", "monster waves", "killer waves", and "king waves") sometimes occur, up to heights near 30 meters, and being much higher than the other waves in the sea state.

Surf’s Up!The Endless Voyage Series

• http://learning.aliant.net/Player/ALC_Player.asp?ProgID=INT_ENDVOY13

• Answer the Self-test questions after the video

• 27mins

What are the consequences / impacts of waves?

Positive consequences

• Surfing• Erosion creating spectacular scenery

Negative consequences

• Causing cliffs to collapse• Property damage• Longshore drift – the movement of

beach material along a shoreline