Home General Knowledge GK SPECIAL TOPIC : TIDES
Friday, 18 July 2014 09:41




The tide is the periodic rise and fall of the sea levels caused by the combined effects of the gravitational forces exerted by the Moon and Sun and rotation of the earth. Most places in the ocean usually experience two high tides and two low tides each day (semidiurnal tide), but some locations experience only one high and one low tide each day (diurnal tide). The times and amplitude of the tides at the coast are influenced by the alignment of the Sun and Moon, by the depth of the ocean, and by the shape of the coastline and near-shore bathymetry.

The moon, which is approximately 240,000 miles (386,240 km) from the earth, exerts a greater influence on the tides than does the sun, which is 93 million miles (150 million km) from the earth. The strength of the sun's gravity is 179 times that of the moon's but the moon is responsible for 56% of the earth's tidal energy while the sun claims responsibility for a mere 44%.

When the moon exerts gravitational force on the earth the tidal bulge moves out and causes high tide. Simultaneously on the side opposite to that place on the earth i.e. just at 1800 to it, also experiences the tidal bulge due to reactionary force (centrifugal) of the gravitational (centripetal) force. Thus two tides are experienced twice at every place on the earth’s water surface within 24 hours.

Due to the cyclic rotation of the earth and moon, the tidal cycle is 24 hours and 52 minutes long.


Spring tides are especially strong tides or high tides. They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides. Spring tides occur during the full moon and the new moon.


Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons.

The Bay of Fundy between Nova Scotia and New Brunswick in Canada experiences the world’s greatest tidal range of 50 feet (15.25 meters)