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|Gravitation (universal gravity) is a long-range fundamental interaction in nature to which all material bodies are subjected to. According to the latest data, universal interaction, unlike any other forces, gives a similar acceleration to all bodies without exception and independent of their masses. Mainly, gravitation plays a determining role in space scales. The term gravitation is used also as a name of a 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 is moved, at any point in space, the gravitational potential depends only on the position of the body at a given moment.
Huge space objects - planets, stars and galaxies have a huge mass and hence, create significant gravitational fields. Gravitation - the weakest interaction. However, as it acts at any distances and all masses are positive, gravitation, nevertheless, is a very important force in the universe. For comparison: The total electric charge of these bodies is zero as a substance, as a whole, is electrically neutral. Also gravitation, in contrast to other interactions, universally acts upon all the matter and energy. Objects, on which gravitation does not act, are not found.
Because of this universal nature, gravitation is crucial even for such large-scale effects, such as the structure of galaxies, black holes and the expansion of the universe and also for elementary astronomical phenomena - the orbits of the planets and for the simple attraction towards the surface of the Earth and the falling of bodies.
Gravitation was the first interaction described by 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. The law of universal gravitation by Issac Newton (1687) very well described the common behavior of gravitation. In 1915, Albert Einstein developed the theory “General Relativity”, which explains gravitation more precisely in terms of the space-time curvature.
In strong gravitational fields, while moving at relativistic speeds, the effects of general relativity start to occur:
o Deviation of the law of gravitation from Newton's law;
o Delay of potentials, connected with the final speed of distribution of the gravitational agitations; the occurrence of gravitational waves;
o Effects of nonlinearity: the gravitational waves have a property to act upon each other and hence, the superposition principle of waves in strong fields is not fulfilled;
o Change in geometry of space - time;
o Occurrence of black holes;
One of the important ОТО predictions is gravitational radiation and to date the detection of radiation is not confirmed through direct observation. However, indirect evidence is available about the existence of radiation, particularly: the loss of energy in the binary system with the pulsar PSR B1913+16 - pulsar by Halsey Taylor - well matched with the model, in which, the energy is carried away by gravitational radiation.
Fine effects of gravitation:
Besides the classical effects of gravitational attraction and time delay, the 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, the overcoming of these difficulties was beyond the opportunities of experimenters.
Among them, in particular, it is possible to name the framed dragging of inertial frames (or effect Lens-thirring) and the gravitation-magnetic field. In 2005, an automatic device of NASA Gravity Probe B conducted an unprecedented experiment to accurately measure these effects near Earth but full results of the experiment are yet to be published.
We are used to one’s own gravity. We became used to the fact that all subjects surrounding us have weight. We do not imagine the other way. All the history of life on Earth progressed in the same conditions. For over millions of years, Earth’s gravity never disappeared. Therefore, all organisms living on our planet, have many years ago, already adapted to withstand their own weight.
Bones, which support the body, have formed in the animals in very ancient times. Without bones, animals under the influence of the Earth’s gravity would creep on the ground as soft jellyfish, taken out from water onto the shore.
For millions of years, all our muscles have adapted to move our body and to overcome the Earth’s gravity.
And, everything inside our body is adapted to weightiness conditions. In the heart, we have powerful muscles, meant to continuously pump several kilograms of blood. If we go down towards the legs, the blood flows easily and upwards, into the head, the blood should be supplied with force. All our internal organs are suspended on strong ligaments. If the ligaments are absent, then internal organs would have rolled “downwards” and formed a heap.
Because of constant weightiness, special organs, vestibular apparatus, positioned in the depth of the head behind the ear, were developed in us. It allows us to understand the position of the earth by us and “top” and “bottom”.
The vestibular apparatus are small cavities, filled with liquid. It consists of tiny pebbles. When a person stands, the pebbles lie at the bottom of the cavity. If a person lies down, then the pebbles roll and lie on the side wall. The brain of the person feels it. And the person, even with closed eyes, can immediately indicate where the bottom is.
So, a person is adapted to all conditions, in which he lives on the surface of the Earth. But after all, entirely different conditions could be available in the Universe. Gravity on planets depends upon their sizes. Gravity is six times less on the small moon than on Earth. On huge Jupiter – three times more.||