Causes of Tides
Gravitational Influence of the Moon and Sun
The gravitational pull of the Moon exerts a significant influence on oceanic waters, resulting in tidal bulges on either side of the Earth. As the Moon draws water towards itself, high tide occurs on both the hemisphere facing the Moon and the opposite side. This phenomenon is a consequence of Earth’s rotation and the Moon’s orbit around Earth; it takes approximately 12 hours for Earth to rotate 180 degrees and 12 hours for the Moon to complete an orbit of 6 degrees. Consequently, coastal areas experience tides roughly every 12 hours and 25 minutes.
The gravitational forces of the Earth, Moon, and Sun contribute to the occurrence of tides. The Moon’s gravitational pull is strong enough to influence ocean movements significantly, while the Sun’s effect, although approximately 27 million times larger in mass than the Moon, is mitigated by its greater distance—about 390 times farther away. This distance results in the Sun accounting for roughly 46% of the tidal forces generated compared to the Moon, as confirmed by the National Oceanic and Atmospheric Administration (NOAA).
Centrifugal Force
Centrifugal force also plays a critical role in the dynamics of ocean tides. As the Moon orbits the Earth, the Earth itself undergoes a slight circular motion, producing a centrifugal force in the oceans. This force functions similarly to how water is retained in a bucket when it is swung in a circular arc. As a result, centrifugal force causes the oceans to bulge on the side opposite to the Moon. While the Moon’s gravitational pull is strong enough to attract water towards it, it is not sufficient to overcome all the inertia present on Earth. Consequently, tides occur twice in the world’s oceans: once when the Earth faces the Moon and again when the Earth is on the opposite side of the Moon.
The Tidal Phenomenon
The tidal phenomenon is characterized by the cyclical rise and fall of sea and ocean water levels, which can either increase or decrease. This phenomenon is driven primarily by the gravitational forces exerted by the Moon and the Sun. Observation of sea level changes reveals a periodic pattern that aligns with the shifting positions of the Moon and Sun in relation to Earth. Tides exhibit characteristics of forced waves and partially oscillating currents, as evidenced by vertical and horizontal movements of water, along with tidal streams.
Significance of Tides
The significance of tides can be summarized as follows:
- Accurate tidal predictions are crucial for maritime activities such as shipping and ocean transportation, facilitating the identification of navigable channels based on weight, ocean depth, and local tidal ranges.
- Low tide conditions attract individuals in coastal regions, enabling fishing nets to effectively capture fish.
- During low tide, it is also possible to collect various marine species, including crabs, clams, and mussels.