Summary of Tides

Tides Overview

• Tides are forced waves induced by spatial variations in gravity due to the Earth-Moon system.

Center of Mass

• The Earth-Moon barycenter is located about 1,650 km beneath Earth's surface, given Earth's mass is 81 times that of the Moon.

Equilibrium Theory of Tides

• Assumes seafloor has no influence on tides, Earth is uniformly covered by water, and ocean surface is in equilibrium with acting forces.

Gravitational Force

• Governed by Newton's Law of Universal Gravitation: every mass attracts every other mass.

• Gravitational force is proportional to mass and inversely proportional to the square of distance.

Formation of Tidal Bulges

• Gravitational attraction of the Moon and centrifugal force create two tidal bulges: one facing the Moon, the other on the opposite side.

Tidal Cycle

• The cycle lasts 24 hours and 50 minutes, leading to lunar tides arriving approximately 50 minutes later each day due to Earth’s rotation.

Lunar Day

• The lunar day is 24 hours and 50 minutes long due to Moon's eastward movement.

Factors Affecting Tides

• Declination: Angle of Moon/Sun above/below Earth's equator influences tide height.

• Orbital Factors: Tidal ranges vary; greatest at perigee (closest point) and least at apogee (farthest point).

Tidal Patterns

• Three tidal patterns:

  • Semidiurnal Tides: Two high and two low tides.

  • Diurnal Tides: One high and one low tide.

  • Mixed Tides: Variability in tidal heights and occurrence.

Tidal Records & Predictions

• Tidal records show relationships between spring and neap tides, influenced by lunar phases.

Tidal Currents & Bore Formation

• Significant tidal fluctuations can generate tidal bores in rivers and inlets.

Harnessing Tidal Power

• Tidal currents can be converted into electricity, as seen in facilities like Sihwa Lake in South Korea, generating 254 megawatts.

Organism Strategies in Intertidal Zones

• Organisms have adaptations to combat desiccation, predation, wave action, and sea level rise.