Материал: Андрианова English Thesaurus of Student-Physicist 2013

Surface tension

If you look closely at a dewdrop sparkling in the morning sunlight, you will find that the drop is spherical. The drop takes this shape because of a property of liquid surfaces called surface tension.

Transport phenomena

When a fluid flows through a tube, the basic mechanism that produces the flow is a difference in pressure across the ends of the tube. This pressure difference is responsible for the transport of a mass of fluid from one location to another. The two fundamental processes involved in fluid transport resulting from concentration differences are called diffusion and osmosis.

1.What four states of matter do you know?

2.How solids can be classified?

3.How does gas turn to plasma?

4.What is elastic modulus?

5.What concept does explain difference in volume within the same

mass?

6.Give the definition of Archimedes's principle.

7.What property makes drop spherical?

Exercises

1. Rearrange the letters in the anagrams to form equivalents for the Russian words:

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2. Match the words in A with the words in B to form word combinations:

3.Fill in the gaps with the missing words from the list: amorphous solid, crystalline solid, pressure, elastic modulus, shear

stress, tensile stress,

1.In a _____ the atoms have an ordered structure.

2.In an _____, such as glass, the atoms are arranged almost random-

ly.

3.A material having a large _____ is very stiff and difficult to de-

form.

4.It's important to remember that in _____, the applied force is parallel to the cross-sectional area, whereas in _____ the force is perpendicular to the cross-sectional area.

5.If the person is wearing snowshoes, that force is distributed over the very large area of each snowshoe, so that the _____ at any given point is relatively low and the person doesn't penetrate very deeply into the snow.

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P A R T II

Thermodynamics

UNIT 10

THERMAL PHYSICS

Read the following texts. Study the thesaurus on fig. 10, answer the questions after the texts

How can trapped water blow off the top of a volcano in a giant explosion? What causes a sidewalk or road to fracture and buckle spontaneously when the temperature changes? How can thermal energy be harnessed to do work, running the engines that make everything in modern living possible?

Answering these and related questions is the domain of thermal physics, the study of temperature, heat, and how they affect matter. Quantitative descriptions of thermal phenomena require careful definitions of the concepts of temperature, heat, and internal energy. Heat leads to changes in internal energy and thus to changes in temperature, which cause the expansion or contraction of matter. Such changes can damage roadways and buildings, create stress fractures in metal, and render flexible materials stiff and brittle, the latter resulting in compromised O-rings and the Challenger disaster. Changes in internal energy can also be harnessed for transportation, construction, and food preservation.

Gases are critical in the harnessing of thermal energy to do work. Within normal temperature ranges, a gas acts like a large collection of noninteracting point particles, called an ideal gas. Such gases can be studied on either a macroscopic or microscopic scale. On the macroscopic scale, the pressure, volume, temperature, and number of particles associated with a gas can be related in a single equation known as the ideal gas law. On the microscopic scale, a model called the kinetic theory of gases pictures the components of a gas as small particles. This model will enable us to understand how processes on the atomic scale affect macroscopic properties like pressure, temperature, and internal energy.

Temperature and the Zeroth law of thermodynamics

Temperature is commonly associated with how hot or cold an object feels when we touch it. While our senses provide us with qualitative indi-

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cations of temperature, they are unreliable and often misleading. A metal ice tray feels colder to the hand, for example, than a package of frozen vegetables at the same temperature, due to the fact metals conduct thermal energy more rapidly than a cardboard package. What we need is a reliable and reproducible method of making quantitative measurements that establish the relative "hotness" or "coldness" of objects - a method related solely to temperature. Scientists have developed a variety of thermometers for making such measurements.

When placed in contact with each other, two objects at different initial temperatures will eventually reach a common intermediate temperature. If a cup of hot coffee is cooled with an ice cube, for example, the ice rises in temperature and eventually melts while the temperature of the coffee decreases. Understanding the concept of temperature requires understanding thermal contact and thermal equilibrium. The exchange of energy between two objects because of differences in their temperatures is called heat.

We can summarize these results in a statement known as the zeroth law of thermodynamics (the law of equilibrium): If objects A and В are separately in thermal equilibrium with a third object C, then A and В are in thermal equilibrium with each other.

Thermometers and temperature scales

Thermometers are devices used to measure the temperature of an object or a system. When a thermometer is in thermal contact with a system, energy is exchanged until the thermometer and the system are in thermal equilibrium with each other. For accurate readings, the thermometer must be much smaller than the system, so that the energy the thermometer gains or loses doesn't significantly alter the energy content of the system. All thermometers make use of some physical property that changes with temperature and can be calibrated to make the temperature measurable.

One common thermometer in everyday use consists of a mass of liquid - usually mercury or alcohol - that expands into a glass capillary tube when its temperature rises. In this case the physical property that changes is the volume of a liquid. To serve as an effective thermometer, the change in volume of the liquid with change in temperature must be very nearly constant over the temperature ranges of interest. When the cross-sectional area of the capillary tube is constant as well, the change in volume of the liquid varies linearly with its length along the tube. The

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most common temperature scale in use in the United States is the Fahrenheit scale.

The Constant-Volume Gas Thermometer and the Kelvin Scale

We can construct practical thermometers such as the mercury thermometer, but these types of thermometers don't define temperature in a fundamental way. One thermometer, however, is more fundamental, and offers a way to define temperature and relate it directly to internal energy: the gas thermometer. In a gas thermometer, the temperature readings are nearly independent of the substance used in the thermometer. The behavior observed in this device is the variation of pressure with temperature of a fixed volume of gas.

Absolute zero is used as the basis for the Kelvin temperature scale. The second point is the triple point of water, which is the single temperature and pressure at which water, water vapor, and ice can coexist in equilibrium.

Thermal expansion of solids and liquids

The discussion of the liquid thermometer made use of one of the best-known changes that occur in most substances: As temperature of the substance increases, its volume increases. This phenomenon, known as thermal expansion, plays an important role in numerous applications. Thermal expansion joints, for example, must be included in buildings, concrete highways, and bridges to compensate for changes in dimensions with variations in temperature.

The overall thermal expansion of an object is a consequence of the change in the average separation between its constituent atoms or molecules. To understand this idea, consider how the atoms in a solid substance behave.

Macroscopic description of an ideal gas

The properties of gases are important in a number of thermodynamic processes. Our weather is a good example of the types of processes that depend on the behavior of gases. If we introduce a gas into a container, it expands to fill the container uniformly, with its pressure depending on the size of the container, the temperature, and the amount of gas.

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