The Sea 1 The Sea

The Sea 2 Introductory Question You float motionless in an inner tube, just far enough from the shore that the waves aren’t breaking on top of you. You will You float motionless in an inner tube, just far enough from the shore that the waves aren’t breaking on top of you. You will A. drift shoreward at the speed of the waves B. drift gradually but steadily shoreward C. move in a circle as each wave passes, but make little or no progress toward shore

The Sea 3 Observations about the Sea The sea is rarely calm—it has ripples on it The sea is rarely calm—it has ripples on it The broadest ripples (waves) travel fastest The broadest ripples (waves) travel fastest Waves seem to get steeper near shore Waves seem to get steeper near shore Waves break or crumble near shore Waves break or crumble near shore Waves bend after passing over sandbars Waves bend after passing over sandbars

The Sea 4 4 Questions about the Sea Why are there tides? Why are there tides? Why are the tides much bigger in some places? Why are the tides much bigger in some places? How does water move in a wave on the sea? How does water move in a wave on the sea? Why do waves bend and break near shore? Why do waves bend and break near shore?

The Sea 5 Question 1 Why are there tides? Why are there tides?

The Sea 6 The Tides (Part 1) The moon’s gravity acts on the earth The moon’s gravity acts on the earth The moon’s gravity isn’t uniform The moon’s gravity isn’t uniform The earth’s oceans are pulled out of round The earth’s oceans are pulled out of round

The Sea 7 The Tides (Part 2) There are two tidal bulges in the oceans There are two tidal bulges in the oceans As the earth rotates, these bulges moves As the earth rotates, these bulges moves Almost 2 high and 2 low tides per day Almost 2 high and 2 low tides per day Strongest tides are near equator Strongest tides are near equator Weakest tides are near poles Weakest tides are near poles

The Sea 8 The Sun’s Influence Sun’s gravity affects tides Sun’s gravity affects tides Strongest tides are when moon and sun are aligned Strongest tides are when moon and sun are aligned Weakest tides are when moon and sun are at right angles Weakest tides are when moon and sun are at right angles

The Sea 9 Question 2 Why are the tides much bigger in some places? Why are the tides much bigger in some places?

The Sea 10 Tidal Resonance Water in a confined channel can slosh back and forth Water in a confined channel can slosh back and forth It’s another harmonic oscillator It’s another harmonic oscillator Period depends on inertia and stiffness of the restoring force Period depends on inertia and stiffness of the restoring force If the sloshing time matches the tidal period, resonance occurs If the sloshing time matches the tidal period, resonance occurs

The Sea 11 Standing and Traveling Waves Sloshing involves standing waves Sloshing involves standing waves Water in a finite container has standing wave modes Water in a finite container has standing wave modes Water waves exhibits fixed nodes and antinodes Water waves exhibits fixed nodes and antinodes Open water surf involves traveling waves Open water surf involves traveling waves Water in an infinite sea has traveling wave modes Water in an infinite sea has traveling wave modes Wave crests and troughs shift continuously Wave crests and troughs shift continuously

The Sea 12 Question 3 How does water move in a wave on the sea? How does water move in a wave on the sea?

The Sea 13 Water Waves Sloshing involves deep water waves: the whole liquid moves back and forth Sloshing involves deep water waves: the whole liquid moves back and forth Surface waves only affect the liquid’s top Surface waves only affect the liquid’s top

The Sea 14 Water’s Motion Surface water circles as the wave passes Surface water circles as the wave passes Circling is strongest at surface Circling is strongest at surface Motion is weak about 1/2 wavelength deep Motion is weak about 1/2 wavelength deep

The Sea 15 Introductory Question (revisited) You float motionless in an inner tube, just far enough from the shore that the waves aren’t breaking on top of you. You will You float motionless in an inner tube, just far enough from the shore that the waves aren’t breaking on top of you. You will A. drift shoreward at the speed of the waves B. drift gradually but steadily shoreward C. move in a circle as each wave passes, but make little or no progress toward shore

The Sea 16 Wavelength Longer the wavelength of surface wave, Longer the wavelength of surface wave, faster it travels faster it travels deeper water moves as it passes deeper water moves as it passes more energy it contains for a given amplitude more energy it contains for a given amplitude Tsunamis are very long wavelength, very deep, very high energy waves (and not strictly surface waves, either) Tsunamis are very long wavelength, very deep, very high energy waves (and not strictly surface waves, either)

The Sea 17 Water in a Wave Only the wave travels, the water circles Only the wave travels, the water circles Crests are formed from local water Crests are formed from local water

The Sea 18 Question 4 Why do waves bend and break near shore? Why do waves bend and break near shore?

The Sea 19 Breaking Waves Surface waves slow down in shallow water Surface waves slow down in shallow water Waves bunch as the water gets shallower Waves bunch as the water gets shallower Waves get taller as water gets shallower Waves get taller as water gets shallower Waves break when water can’t form crest Waves break when water can’t form crest Gradually sloping bottom: rolling surf Gradually sloping bottom: rolling surf Steeply sloping bottom: plunging breakers Steeply sloping bottom: plunging breakers

The Sea 20 Changing Wave Speeds Reflection Reflection Wave speed change causes partial reflection Wave speed change causes partial reflection The bigger the change, the more reflection The bigger the change, the more reflection Refraction Refraction Wave speed change can redirect wave Wave speed change can redirect wave Waves bend toward shore as they slow Waves bend toward shore as they slow

The Sea 21 Summary of the Sea The moon’s gravity causes the tides The moon’s gravity causes the tides The tides can cause resonant motion The tides can cause resonant motion Tidal resonances are standing waves Tidal resonances are standing waves The open sea supports traveling waves The open sea supports traveling waves Water moves in circles in those waves Water moves in circles in those waves Waves break when water gets too shallow Waves break when water gets too shallow