Philosophiæ Naturalis Principia Mathematica
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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.
A stone, whirled about in a sling, endeavours to recede from the hand that turns it; and by that endeavour distends the sling, and that with so much the greater force as it is revolved with the greater velocity; and as soon as ever it is let go, it flies away.
Scholium. Hitherto I have laid down the definitions of such words as are less known, and explained the sense in which I would have them to be understood in the following discourse. I do not define time, space, place and motion, as being well known to all.
Fourth: absolute motion is the translation of a body from one absolute place into another, and relative motion the translation from one relative place into another.
It is a property of motion that the parts which retain given positions to their wholes do partake of the motions of those wholes. For all the parts of revolving bodies endeavour to recede from the axis of motion, and the impetus of bodies moving forward arises from the joint impetus of all the parts.
The effects which distinguish absolute from relative motion are the forces of receding from the axis of circular motion. For there are no such forces in a circular motion purely relative; but in a true and absolute circular motion they are greater or less, according to the quantity of the motion.
But now, if in that space some remote bodies were placed that kept always a given position one to another, as the fixed stars do in our regions, we could not indeed determine, from the relative translation of the globes among those bodies, whether the motion belonged to the globes or to the bodies.
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.
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