The history
From impetus to solar sails: 1,500 years of learning what a moving thing carries.
Philosophers from Philoponus to Buridan guessed that a moving body carries its own 'impetus', growing with its matter and its speed. Descartes turned it into a conserved quantity, but forgot direction; Wallis, Wren and Huygens fixed it in 1668, and Newton built his mechanics on it. A fifty-year quarrel with Leibniz separated momentum from energy. Since then momentum has launched rockets, designed crumple zones and, with light itself, sailed a spacecraft to Venus.
c. 1350
Impetus grows with matter and speed
Jean Buridan, Paris
1644
A conservation law of motion
René Descartes, Amsterdam
1668–69
Correct laws of collision, with direction
Wallis, Wren and Huygens, Royal Society
1687
Momentum as the quantity forces change
Isaac Newton, Principia
1900
Light pressure measured
Pyotr Lebedev, Moscow
1903
The rocket equation
Konstantin Tsiolkovsky, Kaluga
1959
Car built with crumple zones
Mercedes-Benz W111, Béla Barényi's design
2010
Interplanetary solar sail
IKAROS, JAXA
500 – 1600
Philoponus, Ibn Sina and Buridan give a moving body its own impetus, growing with matter and speed.
530
c. 530
Aristotle had said the air keeps a thrown stone moving. Philoponus disagreed: the thrower gives the stone an inner 'impressed force' that slowly wears away. It was the first hint that motion is something a body carries with it.
Why it mattered. It moved the cause of motion from the air into the moving thing itself.
1020
c. 1020
In his Book of Healing, Ibn Sina argued that a thrown body receives an inclination (mayl) that would last forever in empty space; only the air's resistance uses it up. It is close to the modern idea that motion needs no push to continue.
Why it mattered. He imagined motion that never runs down, centuries before Galileo and Newton.
1350
c. 1350 (attributed)
Buridan taught that a mover gives a body 'impetus', and that it grows with both the body's quantity of matter and its speed. That is why a heavy iron ball thrown fast goes further than a light one. Only air and gravity wear it down.
Why it mattered. Mass times speed: the recipe for momentum, three hundred years early.
1640 – 1690
Descartes conserves it, Huygens, Wallis and Wren fix it with direction, Mariotte tests it, Newton makes it law.
1644
In his Principles of Philosophy, Descartes said God keeps the total 'quantity of motion', size times speed, the same in the universe for ever. He also gave seven rules for collisions. Most were wrong, because he ignored direction: speed has no sign, but motion does.
Why it mattered. The first conservation law of motion, and a famous mistake that pushed others to fix it.
1656
1656 (published 1703)
Huygens worked out correct rules for colliding hard balls by picturing the same collision seen from a boat drifting along a canal. He found that mass times velocity, counted with direction, is conserved, and for hard balls mass times speed squared too. His book De motu corporum ex percussione was only printed after his death.
Why it mattered. It fixed Descartes's rules and hinted that there are two conserved quantities, not one.
1668
Nov 1668 – Jan 1669
The Royal Society asked for the true laws of collision. Wallis sent rules for soft bodies that stick (26 November 1668); Wren's rules for hard, bouncing bodies were read on 17 December and printed on 11 January 1669; Huygens sent his too. All three rested on the same idea: the total momentum, counted with direction, never changes.
Why it mattered. The conservation of momentum became an agreed, tested law of nature.
1673
In his Traité de la percussion, Mariotte tested collisions with balls hung on threads, the arrangement we now call Newton's cradle, and sorted collisions into elastic and inelastic ones. Newton later credited his pendulum experiments.
Why it mattered. The first recorded Newton's cradle, a century before Newton's name was attached to it.
1687
Newton's Principia defines 'quantity of motion' as velocity and quantity of matter together, and his second law says a force changes it. Conservation of momentum drops out as a corollary of his laws. He credits Wren, Wallis, Huygens and Mariotte for the collision experiments.
Why it mattered. Momentum became the quantity that forces change, the basis of all later mechanics (see NewtonClear).
1686 – 1745
Leibniz's vis viva, 's Gravesande's clay and du Châtelet's book separate m v from m v².
1686
In the journal Acta Eruditorum, Leibniz published a 'brief demonstration of a notable error of Descartes'. The true 'living force' (vis viva) of a moving body, he said, is mass times speed squared, not mass times speed. Cartesians fought back, and the vis viva controversy lasted about fifty years.
Why it mattered. It separated the ideas we now call momentum and kinetic energy.
1722
's Gravesande dropped brass balls of different masses into soft clay. Balls made equal dents when their heights were inversely proportional to their masses, which means the dent follows mass times speed squared. He switched sides to Leibniz.
Why it mattered. An experiment showing that damage follows energy, not momentum: the myth-buster in this box.
1740
Émilie du Châtelet combined Leibniz's argument with 's Gravesande's clay results in her physics textbook, and argued that vis viva, m v², is what a moving body can do. She later translated Newton's Principia into French.
Why it mattered. She made the energy side of the debate clear and widely read.
1743
In his Traité de dynamique, d'Alembert said the quarrel was partly about words. Measure a force by how long it acts and m v is right; measure it by how far it acts and m v² is right. Today we call these impulse and work.
Why it mattered. It pointed the way to keeping both momentum and energy.
1870 – today
Light's momentum, the rocket equation, Noether's symmetry, crumple zones, airbags and solar sails.
1873
Maxwell's theory of electromagnetism predicted that light carries momentum and presses on anything it hits. The pressure of sunlight on Earth, he worked out, is tiny: a few millionths of a pascal.
Why it mattered. It meant momentum was not just for things with mass.
1900
1899–1900
Lebedev shone light on tiny metal vanes hung in a vacuum and measured the push, announcing it at the 1900 International Congress of Physics in Paris. Nichols and Hull in the USA confirmed it more precisely in 1901–03.
Why it mattered. The first measurement of light's momentum.
1903
May 1903
A schoolteacher in Kaluga published 'Exploration of Outer Space by Means of Reaction Devices' in the journal Nauchnoe Obozrenie. Using momentum conservation for each bit of exhaust, he showed a rocket's final speed is exhaust speed × ln(full mass ÷ empty mass). The issue was confiscated by the police for an unrelated article.
Why it mattered. It showed that spaceflight was possible, and why rockets need stages.
1918
Emmy Noether proved that every symmetry of nature comes with a conserved quantity. Because the laws of physics are the same here as over there, momentum is conserved; because they are the same today as tomorrow, energy is.
Why it mattered. Conservation of momentum turned out to be a property of space itself.
1923
Compton bounced X-rays off electrons and found the X-rays lost energy exactly as if each photon were a tiny ball carrying momentum h ÷ λ. Momentum and energy were both conserved in every photon-electron collision.
Why it mattered. Light's momentum works photon by photon, the rule solar sails rely on.
1959
1952 patent · 1959 car
Barényi split the car into a rigid cabin with front and rear zones designed to fold up in a crash (German patent 854157, 1952). The Mercedes-Benz W111 'Fintail' saloon of 1959 was the first car built fully this way. A longer crush means a longer stop, so less force on the people inside.
Why it mattered. Impulse, F × Δt = Δp, became the rule of car safety.
1967
English actor Simon Prebble named the wooden desk toy made by his company 'Newton's cradle'. Chrome versions soon became an office classic. The idea itself went back to Mariotte, three centuries earlier.
Why it mattered. Momentum and energy conservation on millions of desks.
1974
1973–74 · India 2019–22
GM's Air Cushion Restraint System went into about 11,000 cars from the 1974 model year, starting with the Oldsmobile Toronado. Airbags later became standard worldwide. India made a driver airbag compulsory in 2019 and dual front airbags in all new cars from 2022.
Why it mattered. A cushion of gas makes the head's stop last longer and spreads the force.
2010
20 May 2010
Japan's IKAROS unfolded a 14 m × 14 m sail, thinner than a hair, on its way to Venus. Tracking its orbit, JAXA measured a push of about 1.12 millinewtons from sunlight alone: the first spacecraft to be driven between the planets by light's momentum.
Why it mattered. Light's momentum became a working way to travel through space.
Did you know?
Newton never used the word momentum for m v. He wrote 'quantitas motus', quantity of motion; 'momentum' is Latin for a movement or moving force, and took over during the 1700s.
Descartes's momentum had no direction, so two equal balls meeting head-on and stopping would 'lose' it. Adding a plus or minus sign fixed the whole theory.
The ECE 22.05 helmet test drops a helmeted head at 7.5 m/s onto a steel anvil and allows at most 275 g; the US FMVSS 218 standard allows 400 g.
Tsiolkovsky's 1903 article was hardly read at first: the police confiscated that issue of the journal because of a different, political article in it.
Sunlight pushes on a mirror at about 9 micronewtons per square metre near Earth, roughly the weight of a grain of sand on each square metre, yet IKAROS used it to steer.
The people
c. 1301 – c. 1360 · Philosopher · France
Said impetus grows with a body's matter and speed.
1596 – 1650 · Philosopher and mathematician · France
First to say the quantity of motion is conserved, though his collision rules were mostly wrong.
1629 – 1695 · Physicist and astronomer · Netherlands
Found the correct collision rules by imagining them on a moving boat.
1616 – 1703 · Mathematician · England
Gave the Royal Society the rules for bodies that stick together.
1632 – 1723 · Astronomer and architect · England
Gave the rules for bouncing bodies, before designing St Paul's Cathedral.
c. 1620 – 1684 · Physicist · France
Tested collisions with hanging balls: the first Newton's cradle.
1643 – 1727 · Physicist and mathematician · England
Made quantity of motion the thing forces change.
1646 – 1716 · Philosopher and mathematician · Germany
Argued that m v², not m v, measures a body's 'living force'.
1706 – 1749 · Natural philosopher · France
Brought vis viva and 's Gravesande's clay tests to a wide audience.
1857 – 1935 · Schoolteacher and rocket theorist · Russia
Wrote the rocket equation from momentum conservation.
1882 – 1935 · Mathematician · Germany
Showed momentum is conserved because space is the same everywhere.
1907 – 1997 · Car safety engineer · Austria-Hungary, worked in Germany
Invented the crumple zone and the rigid safety cell.
Where it happened
Sources
Dates marked “c.” are approximate, and historians sometimes disagree about who was first. If you spot a mistake, tell us.
↑↓ move↵ open/ or ⌘K search anywhere