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Физика для колледжа

College Physics 2e

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Бесплатный учебник, по которому учатся миллионы студентов-первокурсников. Первая глава о том, как физика измеряет мир: единицы, степени десяти, перевод единиц, точность, значащие цифры и быстрые оценки.

Это пробная часть: 1 из 34 (главы).

Из лекций

A straight road with a car; two equal road sections of 90 km each, one per hour, add up to 180 km, with the formula d = v t above.
A Few Laws for a Crowded World

Distance is speed times time

Now open the map on that phone. The navigation system, called GPS, leans on one of the simplest relations in physics: the link between speed, distance and time. In words: the distance you cover equals your speed multiplied by the time you keep it up. Where does that come from?

A speed scale in powers of ten from a car to light; the region below one per cent of light speed is shaded as classical; a car and a rocket sit far inside it.
Old Physics, New Physics

Where classical physics holds

Physics as it grew from the Renaissance to the end of the nineteenth century is called classical physics. At the start of the twentieth century, revolutionary discoveries turned it into modern physics.

On the left a metal cylinder under a glass bell with specks of dust on it; an arrow to the right labelled 2019 leads to the letter h for Planck's constant.
A Second, a Metre, a Kilogram

The kilogram leaves its cylinder

Then mass. For a long time the kilogram was simply the mass of one particular cylinder of platinum and iridium, kept with the old metre bar near Paris, with exact copies in other places, including the National Institute of Standards and Technology in Maryland.

30 km per hour times 1000 metres per km times 1 hour per 3600 seconds equals about 8.33 metres per second.
Finishing the Drive Home

Kilometres per hour into metres per second

Now the second request: metres per second. Start from thirty kilometres per hour and use two conversion factors, one turning hours into seconds and one turning kilometres into metres. There are three thousand six hundred seconds in an hour and a thousand metres in a kilometre.

The formula percent uncertainty equals delta A over A times 100 percent, applied to the apple bags: 0.4 over 5.1 times 100 percent is about 8 percent.
Plus or Minus

Percent uncertainty of apples

There is a neat way to compare uncertainties of very different measurements: the percent uncertainty. In words: divide the uncertainty by the measured value, then multiply by a hundred per cent. It tells you how big the uncertainty is compared with the thing being measured.

A tall building with 39 floors; beside one floor two stick figures stacked, 2 metres each, making 4 metres per floor; 39 times 4 metres is 156 metres.
Three Digits, and a Guess at a Trillion

A building measured in people

The first example is a building of thirty-nine floors. The trick is to scale up from something familiar: a person. An adult is about two metres tall, and one floor is roughly the height of two adults, about four metres.

Как это сделано

Примеры для: a curious adult with school maths; add one modern instance per idea, such as a phone, a GPS, a kitchen scale, a car speedometer or a medicine dose

Источник

Лекции пересказывают с английского оригинала книгу OpenStax College Physics 2e, CC BY 4.0 edition (GitHub openstax/osbooks-college-physics-bundle at f98d7a792138), автор — Пол Питер Уроне, Роджер Хинрикс (OpenStax); книга вышла под открытой лицензией, которая разрешает пересказ и перевод. Пересказ, рисунки и голос сделаны ИИ и сверены с книгой второй моделью. Как используется ИИ.

Лекции — переработка оригинала и распространяются под той же лицензией: их можно свободно распространять и перерабатывать с указанием автора и ссылкой на эту страницу: CC BY 4.0

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