Section 4 Text 2. Physical quantities, standards and units

Key terms: physical quantity, fundamental quantity, derived quanti­ty, standard, standard meter, force, length, time, velocity, yard, foot, charge, volume, arbitrary, acceleration, in terms of, accessible, invariable.

The building blocks of physics are physical quantities in terms of which the laws of physics are expressed. Among these are force, length, time, velocity, frequency, density, temperature, charge, volume, mass, and many others. Many of these terms, such as force and temperature, are part of our everyday vocabulary. When these terms are so used, their meaning may be vague or may differ from their scientific meanings. For the purposes of physics the basic quantities must be defined clearly and precisely.

Physical quantities are often divided into fundamental quantities and derived quantities. But such a division is arbi­trary because a given quantity can be regarded as fundamental in one set of operations and as derived in another. Derived quantities are those whose defining operations are based on measurements of other physical quantities. Examples of quanti­ties usually viewed as derived are velocity, acceleration and volume. Fundamental „quantities are not defined in terms of other physical quantities. Examples of quantities usually viewed as fundamental are length and time. Their operational definitions involve two steps: first, the choice of a standard, and second, the establishment of procedures for comparing the standard in such a way that a number and a unit are determined as the measure of that quantity.

An ideal standard has two characteristics: it is accessible and it is invariable. These two requirements are often incom­patible and a compromise has to be made between them. The familiar *y a rd, foot and inch, for example, come from the practice of using the human arm, foot and upper thumb direct­ly as standards. Today, of course, such rough measurements of length are rarely satisfactory; much less variable standards must be used even at the expense of accessibility.

The first truly international standard of length, was a bar of platinum-irridium alloy called the standard meter, kept at the International Bureau of Weights and Measurements near Paris, France. Historically, the meter was intended to be a convenient fraction (one ten-millionth) of a distance from pole to equator along the meridian line through Paris (10 000 kilometres). However there is a unit of length in Nature much more accurate than the distance between two Scratches on a piece of metal. This is the wavelength of light from any sharp spectral line. The standard meter in France has been calibrated in terms of the number of wavelengths of light of a certain spectral line.

Vocabulary notes

frequency, n

density, n

charge, n

precise, adj

derive, v

vague, adj

regard, v

involve, v

compare, v

access, n

alloy, n

scratch, n, v

частота

густина

заряд

точний

походити, виводити не ясний, туманний вважати

втягувати, бути пов’язаним

порівнювати

доступ

сплав

подряпина; шкрябати

TASKS

І. Pronounce these international words after the teacher and translate them. As you see, the majority of the terms used in physics are international. Try to explain, why?

temperature, magnetic, mass, fundamental, arbitrary, distance, ideal, standard, characteristics, bureau, fraction, distance, equator, meridian, pole, accurate, metal, spectral line, calibrate, divide, procedure, vary, compromise, familiar, satisfy.

ІІ. Read these word combinations after the teacher. In group B find their Ukrainian equivalents.

A: building blocks, physical quantities, in terms of, laws of physics, for the purposes of physics, fundamental quan­tities, derived quantities, a set of operations, quantities

usually regarded as derived, operational definitions, in such a way, to be intended, a convenient fracture, wavelength of light, upper thumb, rough measurement, at the expense of

В: основні (базові) величини, величини, які звичайно вважають похідними, наближене вимірювання, фізичні величини, за рахунок, у термінах (мовою), закони фізики, великий палець, таким чином, бути при­значеним, зручна частина, визначення операцій, ряд операцій, складові частини, для фізичних цілей, похідні - величини, довжина хвилі світла

ІІІ. Read and translate these word, analyse to what part of speech they belong.

physics — physical — physically

force — enforce - forced d

ense ~ density — densely

purpose — purposeful - purposeless

precise — precision — precisian

derive т derivative - derivation — derivational

regard ^— regardless — regarding

quantity — quantitative — quantization

operate — operation - operational — operator

involve — involved - involvement

compare — comparison — comparable — comparative

measure — measurement - measured - immeasurable

access — accessible - accessibility — un accessible

intend — intension - intentional - unintentional

convenient — convenience — inconvenient

rough — roughly - roughness

rare — rarely — rarity - rarefy

magnet - magnetic - magnetize

idea — ideal — ideally

pole — polar — polarization

accurate — accurateness — inaccurately

IV. Answer the questions on the text.

1. In what terms are the laws of physics explained? 2. What physical quantities do you know? 3. Into what two groups are physical quantities often divided? 4. Why is this division arbi­trary? 5. What quantities are called derived? Give some examples of derived quantities usually viewed as derived. 6. What are fundamental quantities? 7. What steps do the operational definitions of fundamental quantities involve? 8. What characteristics has an ideal standard. 9. What were standards of length in ancient times? 10. What is the first international standard of length? 11. Where is it kept? What is it equivalent to? 12. What unit of length is more accurate than the standard meter?

ROLE-PLAYING

Imagine that you are a teacher of Physics at a college. The theme of the lesson is «Physical quantities». How would you organise: a) the work at the lesson; b) the test on this theme.

WRITTEN PRACTICE

Write about the international unit of length.

_____________________________

Keys to the crossword.

Across: 1. safe, 3. friend, 4. cry, 6. low, 9. custom, 13. sky, 14. climate,

18. personal, 19. son, 20. weather, 21.winter, 22. goat, 23. ate,

24. forecast, 26. sun, 27. radio, 29. radium

Down: 2. frost, 3. flu, 5. rain, 7. fog, 8. cloudy, 10. stranger, 11.test, 12. mine,

14. cover, 15. inner, 16. inert, 17. target, 18. personal, 19. son,

21. wrong, 25. car, 28. day.