Historical figure · Pearson Edexcel International GCSE revision on Incandio
René Descartes
Who Conserved The Quantity Of Motion · Philosopher & Mathematician · 1596–1650
Who declared that God conserves in the world always the same quantity of motion — and defined that quantity as size multiplied by speed, with no direction in it, which is why six of his seven rules of collision are wrong.
Defend these ideas against Descartes
Incandio is a free revision platform for the Pearson Edexcel International GCSE, and on it a topic counts as mastered only once you have learned it, proved it in questions, taught it back and defended it against the person with the strongest claim on it. René Descartes is that person for 3 topics on the course:
- Momentum — Physics
- Straight Lines: y = mx + c — Mathematics
- Powers, Roots & Index Laws — Mathematics
Who was Descartes?
René Descartes was born in 1596 at La Haye in Touraine, educated by the Jesuits at La Flèche, and spent most of his working life in the Dutch Republic, where he could think without much interference. His Principia Philosophiae of 1644 sets out a complete physics on a small number of principles: body is extension, the world is matter in motion, and God, being immutable, conserves always the same total quantity of motion. He defined that quantity as the size of a body multiplied by its speed, and from it derived three laws of nature — a body persists in the state it is in; all motion of itself is rectilinear; and the rules of what happens when two bodies collide. The first two stand and are the ancestors of Newton's first law. The seven collision rules do not. Christiaan Huygens showed why: speed is a bare magnitude, and a quantity with no direction in it cannot be conserved through a rebound, where the direction reverses. Descartes' fourth rule — that a body at rest can never be set moving by a smaller body however fast it arrives — is contradicted by anybody with two coins. He also refused gravity as an attraction acting across a distance, calling such things occult qualities, and replaced it with vortices of subtle matter carrying the planets round like straws in a whirlpool. His mathematics has worn better than his physics: analytic geometry, in which a curve becomes an equation, is his. He died at Stockholm in 1650, having accepted Queen Christina's invitation to teach her philosophy at five in the morning through a Swedish winter.
Major achievements
- Stated that the total quantity of motion in the world is conserved — the first conservation law in physics
- Formulated the principle that a body persists in its state of motion, the ancestor of Newton's first law
- Stated that motion of itself is in a straight line, so that curved motion needs a cause
- Created analytic geometry, joining algebra to geometry through coordinates
- Gave the sine law of refraction its European currency
Life in brief
- 1596 — Born at La Haye: Educated by the Jesuits at La Flèche.
- 1618 — Meets Isaac Beeckman: Turned toward mechanics and mathematics.
- 1637 — Discourse on Method: With the Geometry, which joins algebra to curves.
- 1644 — Principia Philosophiae: The conservation of the quantity of motion, and the seven rules of impact.
- 1649 — Goes to Sweden: Philosophy lessons for Queen Christina at five in the morning.
- 1650 — Dies at Stockholm: Huygens corrects the collision rules within twenty years.
Explore the life of Descartes — five chapters
- La Flèche, and the Room With the Stove — A Jesuit education rejected on its own terms
- A Curve Becomes an Equation — The Geometry, 1637
- The First Conservation Law — God does not change his mind
- Six Rules Out of Seven Are Wrong — Two coins, and whirlpools carrying the planets
- Five in the Morning in Stockholm — A queen, a winter, and the end
Read the five-chapter life of René Descartes →
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