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.
Here is the heart of the matter. The world is enormously varied: birds flying in formation, flowers of every colour, lightning, gravity, the smallest particles and the largest clusters of galaxies. Over centuries people have gathered mountains of facts about all of it.
The way of working behind all this has a long history.
The second used to be a fraction of an average day, but the Earth's spin is slowly getting slower, so the day is getting longer and is no good as a fixed standard.
With so many sizes, we constantly have to switch from one unit to another. A European recipe gives milk in liters and you want cups; a map gives a walk in feet and you want miles; a medicine label gives a dose in milligrams and you want to know how much that is in grams.
Why should anyone care? The book's answer is a sick child and a thermometer. If the thermometer could be off by three degrees Celsius, a normal reading of thirty-seven might really mean anything from a dangerously cold thirty-four to a dangerous fever of forty.
Then the book turns the question around. Often scientists and engineers do not need many digits at all; they need a quick, sensible estimate, which the book calls a guesstimate. How far is it to a certain place, how dense is a certain object, roughly how much current flows in a circuit?
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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