№1

Units of measurement

Measurement is very important in physics. Every measurement – a distance, a weight, an interval of time, etc., requires two things: a number and a unit. We may, for example, obtain as the result of the measurement of different distances, 20 feet, 5 miles, or the result of the measurement of different weights, 6 pounds, 25 tons, 4 ounces, or as the result of the measurement of different time intervals, 7 hours, 26 seconds, etc. As the result of an experiment we may get the measurements 10 calories, 90 horsepowers, 6 volts, 12 kilowatts, etc. In each case, the unit is as essential as the number which expresses the amount.

Although there are numerous different units, we can express each unit in terms of not more than three special units. These three fundamental units are the units of length, mass, and time. All other units are derived units, as we can always write them as some combination of three fundamental units.

There are in general two sets of fundamental units: a) the metric, b) the English. Throughout the world, scientists express scientific observations nearly always in terms of metric units. This set uses the standard meter as the unit of length, the standard kilogram as the unit of mass, and the second as the unit of time. The standard meter is a platinum-irridium bar. It has 100 equal parts, centimeters.

To measure large distances it is convenient to use large units of length. Such units are the kilometer in the metric system and the mile in the English system. One kilometer is equivalent to 1000 meters, and one mile is equivalent to 5280 ft (feet).

Words to be remembered:

measurement

unit

etc. = et cetera

mile

pound

ounce

horsepower

essential

bar

observation

измерение

единица

и так далее

миля

фунт

унция

лошадиная сила

необходимый, существенный

брусок

наблюдение

№ 2

Gravity and falling bodies

In the absence of friction, all bodies, large and small, fall with the same acceleration. This law of falling bodies is a physical paradox for it contradicts the conclusion a person may come to from general observations. There is nothing to wonder at, for centuries ago the great philosopher Aristotle taught that heavy bodies fall proportionately faster than lighter bodies.

After nearly 2000 years, in the year 1590 Galileo was thinking over the question of falling bodies. He found apparent inconsistencies in Aristotle’s teachings. At tests, he dropped various kinds of objects from different levels of the leaning tower of Pisa and timed their fall and measured their velocities.

Once Galileo attracted a lot of people to the leaning tower. From the top of the tower he dropped two stones, one large and one small. These two bodies fell side by side and struck the ground together. That was the beginning of a new era in science. The importance of Galileo’s many experiments is not in the fact that they demonstrated the mistakes of Aristotle’s reasoning, but that they give the world a new scientific method, the method of experimentation.

It is easy to repeat Galileo’s experiment. Take a coin and a small piece of paper and drop them simultaneously from the same height to the floor. The coin will fall down fast, while the piece of paper will be in the air for a much longer period of time. If you crumple the piece of paper and roll it into a little ball, it will fall almost as fast as the coin. But if you have a long glass cylinder evacuated of air, you will see that a coin and an uncrumpled piece of paper will fall inside the cylinder at exactly the same time.