The river – the most "mobile" type of a reservoir from all their variety presented on our planet. Water in the rivers is in the constant movement: sometimes - rough and prompt, and sometimes – noticeable only to devices. The constant movement of the rivers is explained by natural laws of physics.
The solution is in the substance filling the rivers – in water. Natural property of water, as well as any liquid, fluidity is. Fluidity, in turn, is dictated by forces of an attraction of our planet (for example, in weightlessness state water does not flow, and takes spherical shape). Force of terrestrial gravitation forces water a leak. About 70% of a surface of our planet are covered with water, them which about 67% are the share of the World Ocean. Global sea level is considered the initial point of measurement of height of any land as the overwhelming part of the earth's surface which is not occupied with the ocean is located above this level (height of Everest, the highest top of the world is 8848 meters above sea level). On a land surface (and sometimes under its surface) all known rivers flow. A starting point in the movement of any river is its source. It can be various: spring, lake, swamp or other other reservoir. Finishes the way the river in the mouth which can be the ocean, the sea, the lake or other river. The distance between a source and the mouth can make from several dozen meters to thousands of kilometers (length of Amazon – the longest river – about 7000 km.). The principle of the movement of water weight in the river is that the source always is above the mouth, and, the difference can be very considerable. Povinuyas to laws of fluidity and terrestrial gravitation, water will roll down from higher point down, yet will not reach minimum admissible height – the mouth. It is necessary to tell that waters of not all rivers as a result get to the World Ocean, for example, the Volga River flows into the Caspian Sea – absolutely isolated water system which, however, is located even below universal level: on 28 meters. Despite the enormous volume of the general drain, oceans are not overflowed, and the rivers shallow as the water lost by them is returned to sources again by means of precipitation which main source are just oceans and the seas - so-called water cycle in the nature. The watercourse is similar to running off of water in the water hill of aquapark, but this process is dragged considerably more out to temporary and spatial measures, and therefore to visually define it happens very difficult.