13.6 Tidal Forces

Tidal forces shape our oceans and celestial bodies. The Moon and Sun's gravity create tidal bulges on Earth, causing high and low tides as our planet rotates. These forces also affect other celestial objects, leading to phenomena like tidal locking and heating.

Tides come in different patterns, with spring tides occurring during new and full moons, and neap tides during quarter moons. Understanding tidal forces helps us grasp Earth's rhythms and the complex interactions between celestial bodies in our universe.

Tidal Forces and Their Effects

Gravitational causes of ocean tides

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• Tidal forces generated by gravitational pull of the Moon and the Sun on Earth
  • Moon's gravitational force primary cause of tides due to proximity to Earth (Moon)
  • Sun's gravitational force also contributes to tides, although to a lesser extent than the Moon (Sun)
• Tidal bulges form on Earth due to differential gravitational pull on different parts of the planet
  • Side of Earth closest to the Moon experiences stronger gravitational pull, creating a bulge (high tide)
  • Side of Earth farthest from the Moon also experiences a bulge due to weaker gravitational pull and Earth's tendency to move away from the Moon (high tide on opposite side)
  • This differential pull is known as the gravitational gradient
• Earth's rotation causes tidal bulges to move, resulting in high and low tides
  • As Earth rotates, different parts of the planet face the Moon, causing tidal bulges to shift (Earth's rotation)
  • High tides occur when a location is aligned with either of the tidal bulges (alignment with bulges)
  • Low tides occur when a location is perpendicular to the tidal bulges (perpendicular to bulges)

Neap vs spring tides

• Neap tides occur when gravitational forces of the Moon and Sun are perpendicular to each other
  • During first and third quarter phases of the Moon, the Sun and Moon are at right angles to Earth (quarter moon phases)
  • Gravitational forces of the Moon and Sun partially cancel each other out, resulting in weaker tides (force cancellation)
  • Neap tides have smaller tidal range, with lower high tides and higher low tides compared to average (smaller tidal range)
• Spring tides occur when gravitational forces of the Moon and Sun are aligned
  • During new and full moon phases, the Sun, Moon, and Earth are in a straight line (new and full moon)
  • Gravitational forces of the Moon and Sun combine, resulting in stronger tides (force combination)
  • Spring tides have larger tidal range, with higher high tides and lower low tides compared to average (larger tidal range)
• Tidal range is the difference in water level between high and low tides
  • Neap tides have smaller tidal range compared to spring tides (neap tide range)
  • Spring tides have larger tidal range compared to neap tides (spring tide range)

Tidal forces on celestial bodies

• Tidal forces can cause tidal locking in binary star systems and other celestial bodies
  • Tidal locking occurs when orbital period of a celestial body matches its rotational period (synchronized periods)
  • Gravitational pull of the larger body causes the smaller body to always face the same side towards it (locked orientation)
  • Examples of tidal locking include Earth's Moon and some moons of Jupiter and Saturn (tidally locked moons)
• Tidal heating can occur in celestial bodies due to flexing caused by tidal forces
  • As a celestial body is stretched and compressed by tidal forces, internal friction generates heat (friction-induced heating)
  • Tidal heating can lead to volcanic activity and formation of a subsurface ocean, as seen on Jupiter's moon Io (Io's volcanism)
• Tidal disruption can occur when a celestial body passes too close to a more massive object
  • Strong tidal forces can tear the smaller body apart, creating debris or forming rings around the larger object (tidal shredding)
  • Examples of tidal disruption include comet Shoemaker-Levy 9, which was torn apart by Jupiter's tidal forces before impacting the planet (Shoemaker-Levy 9)

Tidal Theories and Patterns

• Equilibrium theory explains ideal tidal behavior in a simplified model
  • Assumes Earth is covered by a uniform layer of water with no landmasses
  • Provides a baseline for understanding tidal forces and their effects
• Dynamic theory accounts for real-world factors affecting tides
  • Considers the effects of landmasses, ocean basins, and water inertia on tidal patterns
  • Explains variations in tidal patterns observed in different locations
• Tidal patterns vary depending on location and other factors
  • Semidiurnal tides occur twice daily, with two high tides and two low tides of similar height
  • Diurnal tides occur once daily, with one high tide and one low tide
  • Mixed tides combine elements of both semidiurnal and diurnal patterns
• Amphidromic points are locations in oceans where tidal range is nearly zero
  • Act as nodes around which tidal waves rotate
  • Influence tidal patterns in surrounding areas