Philosophiæ Naturalis Principia Mathematica
The same text, told at every level, in every language and look shown here. Pick, then listen or download.
The same player the product gives for your own book: the voice, the drawings as they are drawn, the text.
The book that founded physics. Its opening chapter defines mass, momentum and force, and asks what it means to move at all: absolute and relative time, space and motion, with the spinning bucket and the two globes on a cord.
This is a sample: 1 of 5 chapters.
Put your phone flat on the passenger seat of a car and open any free sensor app that shows the accelerometer. On a straight road at steady speed the reading barely moves. When the driver brakes, the reading jumps and a loose bag on the seat slides forward.
Newton gives each measure a home. Weight belongs to the body, as the sum of the pulls on all its little parts. The speed-up belongs to the place, like a power spread out from the centre to every spot around it.
Motion splits the same way. True motion is a body's passage from one true place to another; relative motion is its passage from one place to another among the things around it.
Space is like time: its parts keep their order forever, and moving a part of space out of its place would be moving it out of itself. Those unmoving parts are the true places, and passing out of them is the only true motion.
And the effect that gives true motion away is the outward strain of spinning. A merely relative circling produces no outward strain; a true spinning does, more the faster it spins. This is where the bucket comes in.
The cord between the two balls is pulled tight by their outward strain, so its tightness tells how fast they spin. Push both balls at once on matching sides: if the cord tightens, the push sped them up, and that reveals which way they are turning.
Examples for: a curious adult with school physics who uses a smartphone every day; add one modern instance per idea, such as GPS satellites, a phone's accelerometer or a car braking
The lectures retell the English text of Project Gutenberg #76404, Andrew Motte's translation (first American edition, 1846). The author died in 1727; the work is in the public domain. The retelling, the drawings and the voice are made by AI and checked against the book by a second model; nothing was edited by hand. How AI is used.
The lectures are free to read, share and quote with a link to this page.
Upload a textbook or any difficult book. The first five minutes are free.
Upload a book