SYSTEMS OF MEASUREMENTS

Unit is a quantity or dimension adopted as a standard measurement. Much physics deals with measurements of physical quantities such as length, time, velocity, area, volume, mass, density, temperature and energy. Many of these quantities are interrelated. For example, velocity is length divided by time. Density is mass divided by volume. Volume is a length times a second length. Most of the physical quantities are related to length, time and mass, therefore all the systems of physical units are derived from these three fundamental units.

Practically there are three main systems of measurements in use today: the British system of units, the Metric system of units and the SI (System of International Units).All the nations of the world use the Metric system. The value of the MKS system (meter-kilogram-second) is that various units show simple and logical relationships among themselves, while the British system fps (foot-pound-second) is very complicated. For example, in the British system 1 mile is equal to 1.760 yards; 1 yard is equal to 3 feet, and 1 foot is equal to 12 inches. In the British system converting one unit to another can be carried out by shifts of a decimal point (comma in Russian writing).

The standard meter of the world was defined in the terms of distance from the North pole to the equator. This distance is close to 10.000 kilometers or 10 ⁷ (ten to the seventh power) meters.

By international agreement the standard meter of the world is the distance between two scratches made on a platinum-alloy bar. It is kept at the International Bureau of Weights and Measures in France. In fact the SI units are an internationally agreed coherent system of units derived from the MKS system. The seven basic units are in it: meter (m), kilogram (kg), second (s), ampere (a), Kelvin (k) mole (mol), and candle (cd).

G. Answer the questions to the text “Systems of measurements”.

1. What is a unit?

2. What are the three fundamental units?

3. Why is the metric system widely in use all over the world?

4. What are the units of length in the MKS in the British system?

I. Choose the correct lettered response to complete each numbered statement.

1. An alternate absolute system is based on the dimensions ………….

a. meter, kilogram and second

b. centimeter, gram and second

c. kilometer, gram and centimeter

2. The ohm is the ………….primary unit of electric resistance.

a. first

b. third

c. second

3. The ampere is the ………….. primary unit for measuring electric current.

a. third

b. second

c. first

4. The volt is a unit of electric …………. .

a. voltage

b. resistance

c. current

5. Ampere discovered the mechanical interaction of ………… and the law of their

interaction.

a. currents

b. voltages

c. resistances

6. The international watt is the energy expended per second electric current of one

International ampere under electric pressure of one international ………… .

a. ampere

b. volt

c. ohm

7. …………. discovered the contact difference of potentials.

a. Volta

b. Ampere

c .Ohm

J. Translate the following sentences paying attention to the Tenses of verbs.

1. The three practical units are defined as ohm, ampere and volt.
2. The original ampere was based on the magnetic effect of current instead of the present electro-chemical effect.
3. An alternate absolute system is based on the dimensions: meter, kilogram and second.
4. A fourth unit is required to define all practical units.
5. Electrostatic units are not used with the M.K.S. system.

6. Three practical units: ohm, ampere and volt provide standards for comparison.

7. The volt is the electric pressure.

K. Cross out the word that is wrong.

1. Unit is a (quality/quantity) adopted as a standard of measurement.

2. Foot is a unit of (area/length) in the British system of measurements.

3. Inch is (more/less) than foot is.

4. The kilogram is a unit for measuring time (in M.K.S. system/ in British system ).

5. Velocity is length (multiplied/divided) by time.

6. The second is a unit for measuring time ( in M.K.S. system/in all systems).

7. (Dimension/division) is a mathematical operation.

8. 11.500 cubic feet is the measure of (area/volume).

L. Read this text and find information about two branches of mechanics - kinetics

and dynamics.

Kinematics is the branch of mechanics which is concerned with the phenomena of motion without reference to mass or force of an object or a moving particle. It deals with motion only

from the standpoint of measurements and precise description, while dynamics is concerned with the causes of laws of motion.

A complete description of a moving particle would involve its mass, direction, speed, distance travelled, time, force producing change of speed, etc. However, kinematics describes motion with respect to speed, time, and distance only, while the nature of the particle or object whose motion is under study is not specified. And so, in kinematics we concern ourselves primarily with three physical quantities: 1) the distance between two positions; 2) speed, i.e. how fast a continuous change of position takes place; 3) the time it takes to get from one position

(point, location) to another. Kinematics is not concerned with either the mass of a moving particle or forces producing change of speed.

Generally the word ‘per’ indicates division. For example, “mass per unit volume” means mass divided by volume. By the way, the words “velocity” and “speed” are considered as synonyms unless they are used in technical literature. In the language of science there is a difference in their meaning. While the word “speed” means the rate at which distance is covered, the word “velocity” means speed in a definite direction. Of the two terms “velocity” is much

more often used by physicists ,for it is broader and more convenient.

M. Translate these sentences from English into Russian using new lexical minimum,

get ready to discuss the topic “Kinematics”.

1. Time is a physical concept and its definition is related to certain laws of physics.
2. We divide the mean solar day into 86.400 equal parts and get the unit used to measure time in all three systems, namely one second.
3. The other units of time are the minute (min) and the hour (hr).
4. Kinematics is the branch of mechanics which is concerned with phenomena of motion without reference to mass or force of an object or a moving particle.
5. Dynamics is concerned with the laws of motion.
6. A complete description of a moving particle would involve its mass, direction, speed, distance, time, force producing change of speed.
7. In kinematics we concern with three physical quantities: distance, speed, time.
8. Kinematics is not concerned with either the mass of a moving particle or forces producing change of speed.
9. The word ‘per’ indicates division; e.g. “mass per unit volume” means mass divided by volume.
10. “Velocity” and “speed” are synonyms, but there is a difference between them.
11. The word “speed” means the rate at which distance is covered.
12. The “velocity” means speed in a definite direction.

N. Read and translate from English into Russian the following word-chains.

Effective density, active volume, atomic dimension, critical velocity, fundamental quantity, molecular dimension, standard length, working volume, decimal point, earth surface, phase shift, density coefficient, energy density, wind velocity, proton, atom structure, vector quantity, energy unit.

O. Read and translate the micro text, find the definitions of such words as смещение, скорость,

длина, направление, ускорение, площадь, величина.

Date: 2014-12-28; view: 3119