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.
The third piece of evidence is people's work. Trains that float above their tracks, cloaks that bend light around themselves, and tiny robots that fight cancer cells all rest on the principles of physics. But so do ordinary jobs.
Now the law. A law describes a general pattern in nature in concise language, backed by evidence and repeated experiments, and it can often be written as a single equation. The book's example is Newton's second law of motion: F = ma.
Now the new section: physical quantities and units. The book opens with a striking picture of the Earth and the Moon, and notes that the distance between them, immense as it seems, is a tiny fraction of the distances to other bodies in the sky.
Powers of ten also measure the scale of a number, its order of magnitude. Any number can be written as a number times a power of ten. 800 = 8 × 10², and 450 = 4.5 × 10². Both carry the factor 10², so they share the same order of magnitude.
Weigh the same apple five times on a kitchen scale, lifting it off and putting it back each time. Write down each reading and subtract the smallest from the largest: that range is your scale's precision for this job.
The first example: estimate the height of a 39-storey building. The strategy is to scale up from something familiar, the height of a person. An adult is about 2 m tall, and one storey is about the height of two adults. So the estimate is 2 m/person × 2 persons/storey × 39 storeys = 156 m.
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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