4.6 Ocean Tides and the Moon

The Moon's gravity creates ocean tides on Earth, causing water to bulge on both the near and far sides. As Earth rotates, different areas experience high and low tides, resulting in tidal cycles that vary globally.

Tidal patterns are influenced by the alignment of celestial bodies. Spring tides occur when the Sun and Moon align, while neap tides happen when they're at right angles. The Moon's tidal force is stronger due to its proximity to Earth.

Ocean Tides and the Moon

Moon's gravity and ocean tides

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Top images from around the web for Moon's gravity and ocean tides

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  Tidal Forces – University Physics Volume 1 View original

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• Moon's gravitational pull attracts water on Earth's surface closest to it, creating a bulge known as high tide
  • Occurs on side of Earth facing the Moon
  • This bulge is referred to as the tidal bulge
• Centrifugal force from Earth-Moon system's rotation creates another high tide on opposite side of Earth
  • Equal in magnitude but opposite in direction to Moon's gravitational pull
• Two low tides occur between the high tides where water is pulled away from the surface (Bay of Fundy, Tierra del Fuego)
• Earth's rotation causes different parts of the planet to experience high and low tides, resulting in a tidal cycle (semidiurnal, diurnal)

Celestial alignment and tidal patterns

• Spring tides happen when Sun, Moon, and Earth align during new moon and full moon phases
  • Gravitational forces of Sun and Moon combine, causing higher high tides and lower low tides (Bay of Fundy, Brittany coast)
• Neap tides occur when Sun and Moon are at right angles relative to Earth during first and third quarter moon phases
  • Gravitational forces of Sun and Moon partially cancel each other out
  • Results in lower high tides and higher low tides compared to spring tides (Gulf of Mexico, Mediterranean Sea)

Tidal forces of Moon vs Sun

• Despite Sun's much larger mass, Moon has a more significant effect on Earth's tides
  • Moon is ~400 times closer to Earth than Sun
  • Tidal forces are inversely proportional to the cube of the distance ($F_t \propto \frac{1}{d^3}$)
• Sun's tidal force on Earth is about 46% of Moon's tidal force
  • Sun's influence is more noticeable during spring and neap tides when forces align or partially cancel out (Proxigean spring tide, Perigean spring tide)

Tidal Variations and Measurements

• Tidal range is the difference in height between high tide and low tide
• Gravitational acceleration affects the strength of tidal forces
• Amphidromic points are locations where tidal range is nearly zero