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| | Gravitation (universal gravity) is a long-range fundamental interaction in the nature to which all material bodies are subjected to. According to latest data, universal interaction, unlike any other forces, gives similar acceleration to all bodies without exception and independent of their masses. Mainly, gravitation plays determining role in space scales. Term gravitation is used also as name of chapter in physics, which studies the gravitational interaction.
Within the frameworks of Newton mechanics, gravitational interaction is long-range interaction. It says that in which ever way a massive body moved, at any point in space, gravitational potential depends only on position of the body at a given moment.
Huge space objects - planets, stars and galaxies have huge mass and hence, create significant gravitational fields. Gravitation - weakest interaction. However, as it acts at any distances and all masses are positive, gravitation, nevertheless, is very important force in the universe. For comparison: Total electric charge of these bodies is zero as substance, as a whole, is electrically neutral. Also gravitation, in contrast to other interactions, universally acts upon the entire matter and energy. Objects, on which gravitation does not act, are not found.
Because of universal nature, gravitation is crucial even for such large-scale effects, such as structure of galaxies, black holes and expansion of the universe and also for elementary astronomical phenomena - orbits of planets and for simple attraction towards the surface of the Earth and falling of bodies.
Gravitation was first interaction described by the mathematical theory. In earlier days, Aristotle considered that the objects with various weights fall at different speeds. Only much later, Galileo Galilei experimentally proved that if air resistance is not taken into consideration, then all the bodies accelerated similarly. Law of universal gravitation of Issac Newton (1687) very well described the common behavior of gravitation. In 1915, Albert Einstein developed theory “General Relativity”, which explains gravitation more precisely in terms of space-time curvature.
In strong gravitational fields, while moving at relativistic speeds, effects of general relativity start to occur:
o Deviation of law of gravitation from Newton's law;
o Delay of potentials, connected with final speed of distribution of gravitational agitations; occurrence of gravitational waves;
o Effects of nonlinearity: gravitational waves have property to act upon each other and hence, superposition principle of waves in strong fields is not fulfilled;
o Change in geometry of space - time;
o Occurrence of black holes;
Gravitational radiation:
One of important ОТО predictions is gravitational radiation and till date detection of radiation is not confirmed through direct observations. However, indirect evidences are available about the existence of radiation, particularly: loss of energy in binary system with pulsar PSR B1913+16 - pulsar of Halsey Taylor - well matched with the model, in which, energy is carried away by gravitational radiation.
Fine effects of gravitation:
Besides classical effects of gravitational attraction and time delay, general relativity theory predicts the existence of other gravitation occurrences, which in terrestrial conditions, are rather weak and their detection and experimental proof are therefore rather difficult. Until recently, overcoming of these difficulties was beyond the opportunities of experimenters.
Among them, in particular, it is possible to name framed dragging of inertial frames (or effect Lens-thirring) and gravitation-magnetic field. In 2005, automatic device of NASA Gravity Probe B conducted unprecedented experiment to accurately measure these effects near Earth but full results of experiment are yet to be published. |
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December 25 is not only the biggest holiday for all the Christians in the world, but is also the birthday of Sir Isaac Newton, the father of classical mechanics and the theory of gravitation. The story has it that Newton was sitting under an apple tree when an apple fell on his head - which gave him an inspiration to formulate his gravitational theory.
