Tides

Fig. 10-7

Fig. 10-6

What are tides???? Tide- the periodic, rhythmic rise

and fall of the sea surface - they are essentially huge

standing waves (two waves moving in opposite directions)

Example:

Poughkeepsie,New York

Tide-producing forces

1. Gravity and motions among Earth, Moon, and Sun (causes the bulge toward the moon)

2. Centripetal force “tethers” Moon to Earth

- Inertia- objects at rest will stay at rest or object in motion will say in motion unless acted upon by an external force

- (causes the bulge away from the moon)

Resultant tidal forces

Gravitational force and centripetal force

Resultant force moves ocean water horizontally

Fig. 10-7

Fig. 10-6

Tidal bulges Two equal

and opposite tidal bulges

Earth rotates beneath tidal bulges

Two high tides and two low tides per day Fig. 10-8

In the video clip ; Dr. Hoffman, from Old Dominion University, explains the tides.

Lunar day-24 hours and 50 minutes

Earth has to “catch up” with Moon to reach same position

Moon revolves around Earth every 27.322 days (29.5306 days between full moons)

Fig. 10-9

Time between successive high tides shifts day after day

Moon rises later each successive night

Solar tidal bulges

Tide-producing force of Sun is smaller

Sun much farther away

Month tidal cycle Spring tides

New Moon, Full Moon

Higher than usual high tides

Fig. 10-12

Neap tide First Quarter,

Last Quarter Lower than

usual high tide

Fig. 10-12

Declination of Sun and Moon

Orientation of Sun and Moon is never directly over the equator Sun 23.5o N and S, yearly cycle Moon 28.5o N and S, monthly

cycle Unequal tides

Successive tides different tidal range

Unequal tidal range

Fig. 10-15

Elliptical orbits Perigee

Earth and Moon are closer

Lunar tidal force greater= Higher high tides

Apogee Earth and Moon are

futher away Lunar tidal force

lesser= Lower high tides

Fig. 10-16

Tidal patterns

Diurnal One high, one low tide per lunar day Period of tidal cycle 24 hours 50

minutes Semidiurnal

Two high, two low tides per lunar day Period 12 hours 25 minutes Equal range

Mixed Two high, two low tides per lunar day

Unequal range Most tides are mixed

Standing waves

Forced standing wave caused by tides

Free-standing waves caused by strong winds or seismic disturbances Fig. 10-22

Bay of Fundy Largest tidal range

(spring tide max 17 m)

Shape of basin Oscillation period

close to tidal period

Shoals and narrows to north

Basin oriented toward right (Coriolis moves water toward right)

Fig. 10-24

The video clip shows tides in the Cape Cod Estuary, Massachusetts

The video clip shows tides on Cape Cod Beach, Massachusetts.

Tidal Calendars

http://www.tidelinesonline.com/