College Physics 2e
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The free textbook used by millions of first-year physics students. Its first chapter is about how physics measures the world: units, powers of ten, converting one unit into another, accuracy, significant figures and quick estimates.
This is a sample: 1 of 34 chapters.
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?
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.
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.
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.
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.
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.
Examples for: 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
The lectures retell the English text of OpenStax College Physics 2e, CC BY 4.0 edition (GitHub openstax/osbooks-college-physics-bundle at f98d7a792138) by Paul Peter Urone, Roger Hinrichs (OpenStax), published under an open licence that allows retelling and translation. The retelling, the drawings and the voice are made by AI and checked against the book by a second model. How AI is used.
The lectures adapt the original and are released under the same licence, free to share and adapt with credit to the author and a link to this page: CC BY 4.0
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