Text 2. What is a fluid?

A fluid, in contrast to a solid, is a substance that can flow. Fluids conform to the boundaries of any container in which we put them. They do so because a fluid is a substance that flows because it cannot withstand a shearing stress. It can, however, exert a force in the direction perpendicular to its surface. Some materials, such as pitch, take a long time to conform to the boundaries of a container, but they do so eventually; thus, we classify them as fluids.

You may wonder why we lump liquids and gases together and call them fluids. After all (you may say), liquid water is as different from steam as it is from ice. Actually, it is not. Ice, like other crystalline solids, has its constituent atoms organized in a fairly rigid three-dimensional array called a crystalline lattice. In neither steam nor liquid water, however, is there any such orderly long-range arrangement.

Exercise 14. Match the names of sciences in the list below to the definitions 1 - 5 to answer the questions which of them studies fluids.

Sciences	Definitions
1. mathematics (maths)	a) the branch of biology that deals with heredity and variation in similar or related animals and plants.
2. physics	b) the science that deals with the production, distribution, and consumption of wealth.
3. linguistics	c) the science dealing with quantities magnitudes, forms and their relationship.
4. economics	d) the science of languages which studies their structure, grammar and history.
5. genetics	e) the science dealing with properties, changes, interaction, etc. of matter and energy.

Exercise 15. Read text 3 about fluids. 4 sentences have been removed from the text and given after the text. Choose the most suitable places for each of them. There is one extra sentence which you do not need to use.

Text 3. Fluids and the world around us

Fluids - which include both liquids and gases - play a central role in our daily lives. (1). A rather vital fluid circulates in the human cardiovascular system. There are the fluid ocean and the fluid atmosphere.

In a car, there are fluids in the tires, the gas tank, the radiator, the combustion chamber of the engine, the exhaust manifold, the battery, the air-conditioning system, the windshield wiper reservoir, the lubrication system, and the hydraulic system. (2). The next time you see a large piece of earthmoving machinery, count the hydraulic cylinders that permit the machine to do its work. (3)

We use the kinetic energy of a moving fluid in windmills, and the potential energy of another fluid in hydroelectric power plants. (4). We often travel great distances just to watch fluids move. Perhaps it is time to see what physics can tell us about fluids.

1. Hydraulic means operated via a liquid.

2. Given time, fluids carve the landscape.

3. Physical quantities, that we find useful, are mass and force.

4. We breathe and drink them.

5. Large jet planes have scores of them.

Exercise 16. Discuss the following topics in groups.

1. Gas and its properties.

2. Liquid and its properties.

3. What distinguishes gas from liquid and solids.

Exercise 17. Memorize the following words and word combinations to text 4.

Motion – рух

subject – піддавати (впливу, тощо)

force – сила

stress – навантаження

pour – лити(ся)

pitcher - глечик

lip – край

gravity - сила тяжіння

tilted - нахилений

contribute – робити внесок

arise - виникати

inversely related – обернено пропорційний

exert – 1. спричиняти / створювати (тиск); 2) докладати (зусиль)

width – ширина

unbalanced – неврівноважений, незбалансований

constrict – звужувати

airfoil – аеродинамічний профіль

teardrop – сльоза

airstream – повітряний потік

curved – кривий; викривлений; зігнутий

straight – прямий

aloft – вгорі, у повітрі

laminar flow – ламінарний, упорядкований потік

streamline – обтічний (потік)

disruption – розрив

turbulent flow – турбулентний потік

smooth – рівний, однорідний

rough – нерівний; бурхливий

stochastic – стохастичний, випадковий

equation – рівняння

buoyancy – плавучість

dynamic pressure – динамічний тиск, швидкісний тиск

Exercise 18. Read text 4. Select the key words and expressions for a five-minute conversation with your partners on the following topic: “Bernoulli’s principle application in airplane wing design”.