From Egyptian workers pouring water under a 58-tonne statue to graphite flakes that slide with almost no friction at all: how people learned to measure, tame and explain the force that grips.
People used friction, and fought it, long before anyone could explain it. Leonardo da Vinci wrote down its rules around 1493, Amontons rediscovered them in 1699 and Coulomb tested them with care in 1785, but why they work stayed a puzzle until Bowden and Tabor showed in 1950 that surfaces touch only at the tips of tiny bumps. Meanwhile engineers learned to float machines on oil, and scientists argued for 170 years about why ice is slippery.
Oldest picture of wetting the ground under a sledge
Tomb of Djehutihotep, Egypt
c. 1493
Laws of friction written down
Leonardo da Vinci, Italy
1699
Laws of friction published
Guillaume Amontons, France
1769
Capstan equation
Leonhard Euler
1794
Ball bearing design
Philip Vaughan, Wales
1883
Oil film shown to carry a load
Beauchamp Tower, England
1978
Electronic ABS in a Mercedes-Benz
Bosch and Mercedes-Benz, Germany
2004
Superlubricity measured
Dienwiebel and colleagues, Netherlands
c. 1900 BCEUsing it before explaining it
1900 BCE – 1510
Using it before explaining it
Builders wet the sand under their sledges, and Leonardo da Vinci measures sliding blocks in his notebooks.
1900 BCE
c. 1900 BCE
Water under the sledge
Workers of the nomarch DjehutihotepDeir el-Bersha, Egypt
A painting in the tomb of Djehutihotep shows 172 workers hauling a colossal statue, nearly 6.8 m tall and around 58 tonnes, on a wooden sledge. A man stands on the front of the sledge pouring water onto the sand in its path. In 2014, physicists in Amsterdam showed why: the right amount of water stiffens the sand so the sledge doesn't plough into it, roughly halving the pull needed.
Why it mattered. It is one of the oldest pictures of someone deliberately changing friction.
In his notebooks Leonardo sketched blocks pulled across a table by weights hanging over a pulley. He noted that friction grows with the weight pressing down, does not depend on how much of the block touches, and is about a quarter of the weight for smooth surfaces.
Why it mattered. He found the basic laws of friction two centuries early, but his notes stayed unpublished.
Amontons, Euler and Coulomb find that friction follows the load, not the area, and separate starting friction from sliding friction.
1699
Amontons's laws
Guillaume AmontonsParis, France
Amontons told the Paris Academy of Sciences that friction is proportional to the load and does not depend on the area of contact. Many academicians found the second rule hard to believe, and it had to be checked again.
Why it mattered. These are still the rules engineers use every day: F = μ × N, whatever the size of the block.
In a paper for the Berlin Academy, Euler reasoned that the friction to start an object moving is bigger than the friction while it slides. He showed how to measure friction with an object on a ramp, and worked out the angle at which a weight starts to slide.
Why it mattered. He separated static from kinetic friction and gave us the ramp test in chapter 1.
Euler worked out why sailors can hold a straining ship with a few turns of rope round a post. The force the rope can hold grows exponentially with the angle of wrap: T = T₀ × e^(μθ). Johann Eytelwein published it again in 1808.
Why it mattered. The capstan equation explains bollards, knots and belt drives.
Charles-Augustin de CoulombRochefort and Paris, France
Working at the naval shipyard of Rochefort, Coulomb slid wood and metal over each other under different loads, speeds and times of contact. His prize-winning study of simple machines, published in 1785, confirmed Amontons's laws and found that sliding friction barely changes with speed.
Why it mattered. Dry friction with a constant μ is still called Coulomb friction.
Vaughan designed a carriage axle in which balls ran along a groove, so the parts rolled instead of rubbing. In 1869 a radial ball bearing designed by Jules Suriray helped James Moore win the Paris–Rouen bicycle race.
Why it mattered. Rolling instead of sliding cuts friction enormously: every fan and mixer motor depends on it.
Engineers discover that a film of oil can carry a whole shaft, physicists argue about ice, and a lab accident produces Teflon.
1850
7 June 1850
A wet skin on ice
Michael FaradayRoyal Institution, London, England
Faraday noticed that two pieces of ice pressed together freeze into one, even in warm air. He suggested that ice is covered by a thin film of liquid even below 0 °C. James Thomson and his brother William, later Lord Kelvin, argued instead that pressure melts the ice.
Why it mattered. The argument over why ice is slippery lasted until X-ray studies in the 1980s and 1990s found Faraday's layer.
Testing railway axle bearings for the Institution of Mechanical Engineers, Tower drilled a hole in a bearing and plugged it. The plug kept being forced out by the oil. He measured the pressure and found that the oil film itself was carrying the load.
Why it mattered. It revealed hydrodynamic lubrication: a shaft can float on oil.
Reynolds explained Tower's result: a turning shaft drags oil into the narrowing gap of its bearing, building enough pressure to lift the shaft off the metal. His equation is still used to design engine bearings.
Why it mattered. It turned lubrication from guesswork into engineering.
Joly calculated the pressure under a skate blade at about 466 atmospheres, enough to lower ice's melting point by about 3.5 °C. For decades this pressure-melting idea was the textbook reason skates glide.
Why it mattered. It explained skating near 0 °C, but not why skating works at −20 °C.
Stribeck measured friction in bearings over a range of speeds and loads. Friction was high when starting, fell steeply as an oil film formed, then rose slowly. Adolf Martens had seen the same pattern in 1888.
Why it mattered. The curve shows why engines wear most at start-up.
Roy J. Plunkett and Jack RebokDuPont Jackson Laboratory, New Jersey, USA
Looking for a new refrigerant gas, Plunkett opened a cylinder that should have been full, but nothing came out. Inside was a waxy white solid: the gas had joined up into polytetrafluoroethylene, PTFE. DuPont sold it as Teflon from 1945.
Why it mattered. PTFE has one of the lowest friction coefficients of any solid, about 0.04.
Frank Philip Bowden and T. P. HughesCambridge, England, and the Swiss Alps
Sliding objects over ice and snow at different speeds and temperatures, Bowden and Hughes argued that frictional heating melts a thin layer of water under a sliding ski or skate.
Why it mattered. It explained gliding on very cold ice, where pressure melting can't.
Friction turns out to happen at tiny contact points. Tyres, brakes and spacecraft are designed around it, and at the atomic scale it can almost vanish.
1950
The real area of contact
Frank Philip Bowden and David TaborCambridge, England
In their book The Friction and Lubrication of Solids, Bowden and Tabor showed that surfaces touch only at the tips of their bumps, over a tiny fraction of the area you see. The bumps squash until they can carry the load, so the real contact area grows with the load.
Why it mattered. It finally explained Amontons's laws.
Walter B. Horne and Robert C. DreherNASA Langley Research Center, Virginia, USA
Testing aircraft tyres on flooded runways, NASA engineers found that above a certain speed a tyre lifts right off the ground on a wedge of water. That speed depends on the tyre pressure: about 9 × √(pressure in psi) knots.
Why it mattered. Their rule is still used for aircraft, and helps explain why worn car tyres aquaplane.
Bosch's electronic ABS became an option on the Mercedes-Benz S-Class. Sensors watch each wheel, and valves release the brake pressure many times a second whenever a wheel starts to lock, so the tyres keep rolling with static grip.
Why it mattered. Cars could now brake hard and still steer.
NASA Jet Propulsion LaboratoryOn the way to Jupiter
The Galileo spacecraft tried to open its 4.8 m umbrella-like antenna, but two or three of its 18 ribs stayed stuck. Investigators blamed friction at metal pins whose dry lubricant had been worn away during testing and travel.
Why it mattered. In space, a little too much friction can cripple a mission.
Martin Dienwiebel, Joost Frenken and colleaguesLeiden, Netherlands
With a very sensitive friction microscope, the Leiden team dragged a tiny graphite flake over graphite and turned it. Friction was high only when the flake's atoms lined up with those below, every 60°. In between it almost disappeared.
Why it mattered. It proved that friction can nearly vanish when atomic bumps can't lock together.
Bart Weber, Daniel Bonn, Mischa Bonn and colleaguesAmsterdam, Netherlands, and Mainz, Germany
Measuring steel sliding on ice from −100 °C to 0 °C, and probing the surface with lasers, the team found that the top layer of ice molecules is only loosely bound and moves almost freely. Friction was lowest at about −7 °C, the temperature used on speed-skating rinks.
Why it mattered. It showed that ice is slippery mainly because of its own loose surface, not pressure.