Библиотека · Общественное достояние

Математические началанатуральной философии

Philosophiæ Naturalis Principia Mathematica

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Книга, с которой началась физика. Первая глава определяет массу, количество движения и силу и спрашивает, что вообще значит двигаться: абсолютные и относительные время, пространство и движение, с вращающимся ведром и двумя шарами на верёвке.

Это пробная часть: 1 из 5 (главы).

Из лекций

A car seat with a phone and a bag; the accelerometer trace is flat while the car cruises and jumps when it brakes, while the bag slides forward with nothing pushing it.
Matter, Motion and the Pull Towards a Centre

The Bag Keeps Going

Lay your phone flat on the passenger seat of a car and open any free sensor app that shows the accelerometer. While the car rolls steadily along a straight road, the reading along the direction of travel stays near zero.

Weights compared as bars: a full body here, a half-size body where gravity is halved weighing a quarter, a third-size body weighing a sixth.
One Pull, Three Measures, and Time Itself

Half the Pull, Smaller Bodies

Newton gives each measure a home.

Two time lines, one with perfectly even ticks labelled true time, one with uneven ticks labelled clocks; below them a fixed grid with a box of air carried across it by the moving Earth.
One Pull, Three Measures, and Time Itself

True and Common Time and Space

Time comes first. True, absolute time flows evenly of itself, without regard to anything outside, and its other name is duration. Relative, common time is any visible measure of that duration made by some motion, accurate or not, such as an hour, a day, a month or a year.

A house treated as unmoving, with measured distances to two bodies; behind them a faint fixed grid of true places that cannot be seen; a question mark over the house.
Places, a Sailor, and Why Rest Cannot Be Seen

Places Measured From a Body

But we cannot see the parts of space or tell them apart, so we use measures we can see instead. We pick some body that we treat as unmoving, define every place by its distance and direction from that body, and judge every motion against those places.

Two rows of two boxes, A and B: pushing only B changes their relative motion though A is untouched; pushing both equally keeps their relative position though both truly move.
The Kernel, the Shell and the Spinning Bucket

Push the Other Body

Next, the causes. True motion is never created or changed except by a force pressed on the body itself. Relative motion can change with no force on the body at all: push the things it is compared with instead, and the relation changes.

Two columns: the quantities themselves (time, space, place, motion) on the left and their visible measures (clock, room, position, change against bodies) on the right, with an arrow from each measure to what it measures.
Two Globes in an Empty Sky

Quantities and Their Measures

First, a point about words. The relative quantities, our hours, our measured places, our speeds against the ground, are not the true quantities they are named after, but the visible measures we commonly use instead, accurate or not.

Как это сделано

Примеры для: 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

Источник

Лекции пересказывают английского текст: Project Gutenberg #76404, Andrew Motte's translation (first American edition, 1846). Автор умер в 1727 году; произведение перешло в общественное достояние. Пересказ, рисунки и голос сделаны ИИ и сверены с книгой второй моделью; вручную ничего не правилось. Как используется ИИ.

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