Notes on “Waves & Tides”

Earth/Space

S.W.B.A.T.

• Describe wave formation• Distinguish between the movement

of water particles in a wave and the movement of the wave

• Explain how ocean tides form

Wave Characteristics

• Wave – a rhythmic movement that carries energy through matter and space

• Wind, earthquakes, landslides, the Sun & Moon (tides) all generate waves

Wave Characteristics

• Only the energy moves forward in a wave

• Water particles do not move forward unless a wave is breaking on shore

Wave Characteristics

• The crest, trough, wavelength and wave height describes a wave

• Crest – high point in a wave• Trough – low point

Wave Characteristics

• Wavelength – horizontal distance from crest to crest or trough to trough

• Wave height – vertical distance between crest & trough

Wave Characteristics

• Energy is transmitted through the water in 3-dimensions

• Orbital waves – water particles move in circles or orbits

• This allows energy transfer between liquids and/or gases

Water Orbital Wave Movement

Wave Characteristics

• Other wave characteristics include frequency and fetch

• Frequency – number of wavelengths that pass a fixed point over time

• Fetch – describes speed & constant wind direction over time and distance

Wave Characteristics

• Fetch can create huge waves

• Highest wave ever experienced at sea was over 112ft! (U.S.S. Ramapo 1933)

Wave Characteristics

• Rogue waves – rare and unpredictable ocean waves

• Wave heights are huge & damaging to ships

• Rogue waves are probably the result of extensive fetch and a combining of swells

Ocean Swells Can Combine to Form Larger Waves

Rogue Waves Can Occur in Non-Stormy Seas

Video (1:32) “Rogue Wave Hits Cruise Ship”

Tides

• Tides - gradual rise & fall (high & low) in sea level

• Tides can have a wave height of only 1-2 meters

• However - tide wavelength can be thousands of km long

Tides

• Tides are caused by the gravitational pull of the Sun & Moon

• The Moon exerts a stronger pull because it is closer to Earth

Tides Change as the Earth Rotates and the Moon Orbits the Earth

Tides

• Tidal range – difference between high & low tides

• As Earth rotates its surface passes through both high and low positions

• Most coastlines experience two high and low tides each day – depending on ocean basin shape & size

Mont-Saint-Michel - Normandy, France at High Tide

Mont-Saint-Michel at Low Tide - 13.5m Difference

Tides

• Extreme tidal ranges occur due to shoreline shape

• Bay of Fundy in Nova Scotia, Canada has a tidal range of 15m due to its funnel-like shape

Video (1:52) “Bay of Fundy’s Tides”

Tides

• Spring Tides – when the Moon, Earth & Sun line-up to produce even higher tides

• This happens about twice a month

Tides

• Neap Tides – when the Moon, Earth & Sun are at right-angles

• Gravity is nearly “canceled out” giving very little tidal pull

• This also happens about twice a month

Class Activity

• Many planets have more than one moon

• Explain what tides might be like if Earth had two moons