1.Gravitational pull of the moon and sun

2.Centripetal force of the rotating Earth

Tides are generated by:

Tides are generated by:• the gravitational pull of the moon and sun

- moon has 2x greater gravitational pull than the sun - sun is 10 million x more massive than the

moon and is 390 times farther away

Centripetal force

CENTRIPETAL

GRAVITATIONAL FORCE

GRAVITATIONAL & CENTRIPETAL

• Diurnal Tide: 24 hr 50 min cycle

• Semi Diurnal Tide: 12 hr 25 min cycle

• Mixed Tide: 12 hr 25 min cycle

Tidal Cycles

• High water: a water level maximum ("high tide") • Low water: a water level minimum ("low tide") • Tidal range: the difference between high and low

tide• Spring Tide: full moon and new moon (14.77 days)• Neap Tide: 1st quarter and 3rd quarter (14.77 days)

Description of tides

Intertidal zoneHigh tide

Low tide

The monthly tidal cycle(29½ days)

• About every 7 days, Earth alternates between:– Spring tide

• Alignment of Earth-Moon-Sun system (syzygy)• Lunar and solar bulges constructively interfere• Large tidal range

– Neap tide• Earth-Moon-Sun system at right angles (quadrature)• Lunar and solar bulges destructively interfere• Small tidal range

Earth-Moon-Sun positions and the monthly tidal cycle

Spring TideHighest high tide and lowest low tide

Neap TideModerate tidal range

The Bay of Fundy: Site of the world’s largest tidal range

• Tidal energy is focused by shape and shallowness of bay

• Maximum spring tidal range in Minas Basin = 17 meters (56 feet)

Alma at High Tide

Alma at Low Tide

Corals exposed to air at extreme low tide

Inquiry

1. Which has the greatest tidal effect– sun or moon?

2. Where is the greatest tidal range located?

3. Which lunar phase produces moderate tides?

4. How is a tidal bore created?