Lesson 5.

1. Прочитайте и переведите текст. Hydraulics.

Hydraulics, as commonly understood and applied, is the science deeling with the action and use of the water. Water is the most common luguid. Water is the chemically pure state is not found in nature. Inland waters, which contain varying quantities of salt and mineral matter in solution, occur chiefly as streams, lakes, springs and underground supplies.

Hydraulics units. In all English - speaking countries, the three primary units are the foot, the pound and the second.

There are two important types of hydraulics units: unit of volume and a unit of flow. The most important unit of volume is the cubic foot, in the United States, the gallon /0,13 cu Ft/. The cubic foot per minute is the standard unit of flow, in the United States - the gallon per minute.

Properties of water. A fluid is a substance, which offers very little resistance to change of form and readily takes the shape a solid body – with which it comes in contact.

Compressibility. Though in common water is assumed to be incompressible, it is, like other liquids, slightly compressible. It is also perfectly elastic.

Viscosity. The ability of water to resist movement between its particles is termed viscosity.

It may be described as thick ness.

Adhesion and cohesion cause water to rise above the outside level.

Vocabulary:

flow - течение, поток

fluid - жидкость

compressibility - сжимаемость

viscosity - вязкость

cubic foot - куб. фут. ⁼ 38317,016 см³

gallon - галлон = 4,5459631 дм³.

Adhesion-трение

Cohesion-сцепление

a) Give the definition of hydraulics and viscosity.

2. Ответьте на вопросы.

1. In what state is water found in nature?

2. What hydraulic units do you know?

3. What properties of water do you know?

Lesson 6.

1.Прочитайте и переведите текст.

Ground Water.

Ground water is water contained underground in the interstices of soil and rock. When ram falls on the earth some evaporates, some is absorbed by planets, some runs off in streams and the remainder sinks into the earth to become ground water.

The amount that enters the ground depends on various factors: rain falling on loose soil sinks immediately; rain falling on clay either lies on the surface and evaporates or runs off; on step slopes run off will exceed absorption. Ground water exists everywhere in the earth's crust, generally not much deeper than about a mile.

The upper surface of this water is known as the water table. The height of the water table varies between wet and dry seasons and between humid and arid regions. In deserts the water table may be hundreds of feet below the surface.

The region that is known as the zone of fluctuation. This zone through which the water table fluctuation is the place where decomposition of rock is most active.

The water table rises to higher levels underneath the hills and slopes to lower levels in the valleys, where it may appear on the surface in the form of springs, rivers, bogs and lakes.

This ground water acts directly by taking into solution the soluble minerals (process of solution) and by adding molecules of water to the other minerals (process of hydration) and indirectly by bringing carbon dioxide to be combined with some of the elements in solution, such as calcium, to from carbonates (process of carbonation). Oxygen readily unites with most elements and this combination is made when water is present. As a result we get oxides and hydrated oxides (process of oxidation).