Tidal force

The tidal force is a force that stretches a body towards and away from the center of mass of another body due to a gradient in gravitational field from the other body. It arises because the gravitational field exerted on one body by another is not constant across its parts: the nearest side is attracted more than the farthest side, it is this difference. Thus, the tidal force is known as the differential force, as well as a secondary effect of the gravitational field. In celestial mechanics, the expression tidal force can refer to a situation in which a body or material is under the gravitational influence of a second body, but is perturbed by the gravitational effects of a third body; the perturbing force is sometimes in such cases called a tidal force: it is the difference between the force exerted by the third body on the second and the force exerted by the third body on the first. When a body is acted on by the gravity of another body, the field can vary on body 1 between the side of the body facing body 2 and the side facing away from body 2.

Figure 4 shows the differential force of gravity on a spherical body exerted by another body. These so-called tidal forces cause strains on both bodies and may distort them or in extreme cases, break one or the other apart; the Roche limit is the distance from a planet at which tidal effects would cause an object to disintegrate because the differential force of gravity from the planet overcomes the attraction of the parts of the object for one another. These strains would not occur if the gravitational field were uniform, because a uniform field only causes the entire body to accelerate together in the same direction and at the same rate; the relationship of an astronomical body's size, to its distance from another body influences the magnitude of tidal force. The tidal force acting on an astronomical body, such as the Earth, is directly proportional to the diameter of that astronomical body and inversely proportional to the cube of the distance from another body producing a gravitational attraction, such as the Moon or the Sun.

Tidal action on bath tubs, swimming pools and other small bodies of water is negligible. Figure 3 is a graph showing. In this graph, the attractive force decreases in proportion to the square of the distance, while the slope relative to value decreases in direct proportion to the distance; this is why the gradient or tidal force at any point is inversely proportional to the cube of the distance. The tidal force corresponds to the difference in Y between two points on the graph, with one point on the near side of the body, the other point on the far side; the tidal force becomes larger, when the two points are either farther apart, or when they are more to the left on the graph, meaning closer to the attracting body. For example, the Moon produces a greater tidal force on the Earth than the Sun though the Sun exerts a greater gravitational attraction on the Earth than the Moon, because the gradient is less; the Moon produces a greater tidal force on the Earth, than the tidal force of the Earth on the Moon.

The distance is the same, but the diameter of the Earth is greater than the diameter of the Moon, resulting in a greater tidal force. What matters is not the total gravitational attraction on a body, but the difference from one side to the other; the greater the diameter of the body, the more difference there will be from one side to the other. Gravitational attraction is inversely proportional to the square of the distance from the source; the attraction will be stronger on the side of a body facing the source, weaker on the side away from the source. The tidal force is proportional to the difference; as expected, the table below shows that the distance from the Moon to the Earth, is the same as the distance from the Earth to the Moon. The Earth is 81 times more massive than the Moon but has 4 times its radius; as a result, at the same distance, the tidal force per unit mass of the Earth on the Moon is about 20 times stronger than that of the Moon on the Earth. Thus the Earth was able to lock the Moon's rotation to its orbit around the Earth but not vice versa.

In the case of an infinitesimally small elastic sphere, the effect of a tidal force is to distort the shape of the body without any change in volume. The sphere becomes an ellipsoid with two bulges, pointing away from the other body. Larger objects distort into an ovoid, are compressed, what happens to the Earth's oceans under the action of the Moon; the Earth and Moon rotate about their common center of mass or barycenter, their gravitational attraction provides the centripetal force necessary to maintain this motion. To an observer on the Earth close to this barycenter, the situation is one of the Earth as body 1 acted upon by the gravity of the Moon as body 2. All parts of the Earth are subject to the Moon's gravitational forces, causing the water in the oceans to redistribute, forming bulges on the sides near the Moon and far from the Moon; when a body rotates while subject to tidal forces, internal friction results in the gradual dissipation of its rotational kinetic energy as heat. In the case for the Earth, Earth's Moon, the loss of rotational kinetic energy results in a gain of about 2 milliseconds per century.

If the body is close enoug


Kokaral was until 1973 an island in Kazakhstan, in the northern part of the Aral Sea. It had an area of 273 km², its highest point was the 163 meter high hill called Daut. On its northern shore was situated the fishing villages of Kokaral and Akbasty. Due to the shrinking of the Aral Sea, the island became connected to the mainland in the 1960s at its western end, became the Kokaral Peninsula. From 1987 on it became connected to the surrounding land at its eastern end, over the Berg Strait, turning the peninsula into an isthmus separating the North Aral Sea and the South Aral Sea. In 2005 the Dike Kokaral across the Berg Strait was completed; the dike stops water from the North Aral Sea from spilling over into the South Aral Sea, thus contributes to maintaining and increasing the waterlevel in the northern sea

Lemon Grove, California

Lemon Grove is a city in San Diego County, United States. The population was 25,320 at the 2010 census, up from 24,918 in 2000; the area that became Lemon Grove was part of Mission San Diego de Alcalá, one of the Spanish missions in California. After Mexico became independent from Spain, the Californios ranched on various land grants; the area that now includes Lemon Grove was granted to Santiago Argüello, who received more than 59,000 acres. The first proprietor of Lemon Grove, Robert Allison, arrived in the region in 1850, coming from Sacramento, he purchased thousands of acres from Santiago Argüello's heirs. Allison became a director and stockholder of the San Diego and Cuyamaca Railroad in 1886 and built the Allison Flume. Allison's son Joseph filed subdivision maps for "Lemon Grove" in 1892; the name is attributed to Tempa Waterman Allison. The climate was suitable for the cultivation of subtropical fruits and vegetables, farmers from the East and Midwest flocked to the region; the Lemon Grove Fruit Growers Association was formed in 1893.

The brothers opened A. Sonka and Son. Anthony "Tony" F. Sonka, the eldest son of Anton Sonka and his German American wife Anna Klein Sonka, was a local notable, he was a key supporter of the huge lemon that became the town's landmark. Sonka and a committee of local ranchers hired local architect Alberto Treganza to build the huge lemon to "make the ultimate statement about the town's purpose and optimism."In the Lemon Grove Incident in 1931, Mexican American parents in Lemon Grove pursued a successful judicial challenge against the decision of the local school board to build a separate school for Mexican American pupils. The decision of the Superior Court for San Diego County in Alvarez v. Lemon Grove was the first successful lawsuit against school segregation. By World War II, most of the citrus groves had disappeared and suburbanization had begun. There had been four elections on incorporation from the 1950s to the 1970s; the city was incorporated on July 1, 1977, becoming California's 414th city.

Lemon Grove was incorporated as a general-law city. Lemon Grove is located at 32°44′0″N 117°2′1″W. According to the United States Census Bureau, the city has a total area of 3.9 square miles, all land. The city is served by California State Routes 94 and 125, it is served by the San Diego Trolley's Orange Line, at Lemon Grove Depot as well as at Massachusetts Avenue Station. The 2010 United States Census reported that Lemon Grove had a population of 25,650; the population density was 6,525.3 people per square mile. The racial makeup of Lemon Grove was 8,545 White, 3,495 African American, 225 Native American, 1,628 Asian, 275 Pacific Islander, 4,828 from other races, 1,801 from two or more races. Hispanic or Latino of any race were 11,635 persons; the Census reported that 24,974 people lived in households, 200 lived in non-institutionalized group quarters, 146 were institutionalized. There were 8,434 households, out of which 3,295 had children under the age of 18 living in them, 3,863 were opposite-sex married couples living together, 1,419 had a female householder with no husband present, 601 had a male householder with no wife present.

There were 516 unmarried opposite-sex partnerships, 94 same-sex married couples or partnerships. 1,928 households were made up of individuals and 734 had someone living alone, 65 years of age or older. The average household size was 2.96. There were 5,883 families; the population was spread out with 6,458 people under the age of 18, 2,583 people aged 18 to 24, 6,900 people aged 25 to 44, 6,550 people aged 45 to 64, 2,829 people who were 65 years of age or older. The median age was 35.0 years. For every 100 females, there were 95.3 males. For every 100 females age 18 and over, there were 93.6 males. There were 8,868 housing units at an average density of 2,285.4 per square mile, of which 4,609 were owner-occupied, 3,825 were occupied by renters. The homeowner vacancy rate was 2.0%. 13,984 people lived in owner-occupied housing units and 10,990 people lived in rental housing units. As of the census of 2000, there were 24,918 people, 8,488 households, 5,958 families residing in the city; the population density was 6,557.3 inhabitants per square mile.

There were 8,722 housing units at an average density of 2,295.2 per square mile. The racial makeup of the city was 33.7% White, 13.9% African American, 0.4% Native American, 6.7% Asian, 0.8% Pacific Islander, 13.5% from other races, 7.1% from two or more races. Hispanic or Latino of any race were 45.3% of the population. There were 8,488 households out of which 36.4% had children under the age of 18 living with them, 49.0% were married couples living together, 15.6% had a female householder with no husband present, 29.8% were non-families. 22.4% of all households were made up of individuals and 8.9% had someone living alone wh