110 Fun Facts About Physics

Roughly how fast does light travel through empty space?

Light travels at about 300,000 km per second through empty space, exactly 299,792,458 metres per second; since 1983 the metre has been defined from that speed.

Whose three laws of motion were first published in the Principia in 1687?

Isaac Newton's Principia nearly went unprinted: the Royal Society had spent its book budget on a history of fishes, so the astronomer Edmond Halley paid for publication himself in 1687.

Which SI unit, symbolised by the Greek letter omega, measures electrical resistance?

The ohm honours Georg Ohm, whose 1827 law linking voltage, current and resistance was coldly received; hurt, he resigned his teaching post, and recognition came only with the Royal Society's Copley Medal in 1841.

What phenomenon makes the daytime sky look blue?

Rayleigh scattering by air molecules affects short blue wavelengths far more than long red ones, so scattered blue light fills the sky; the low Sun turns orange as its blue is scattered away.

At 20 °C, how fast does sound travel through air?

Sound moves at about 343 metres per second in air at 20 °C, roughly a kilometre every three seconds, which is why you count between lightning and thunder.

Absolute zero corresponds to which temperature on the Celsius scale?

−273.15 °C is the point where an ideal gas's pressure would shrink to nothing; it can be approached but never reached, though physicists have chilled atoms to within billionths of a degree of it.

Which SI unit of power is named after a Scottish inventor?

Watt honours James Watt, whose separate condenser made steam engines far more efficient; to compare them with the horses they replaced he popularised 'horsepower', and one horsepower is about 746 of the units named after him.

Who received the first Nobel Prize in Physics, in 1901, for discovering X-rays?

Wilhelm Röntgen called the rays 'X' because nobody yet knew what they were; he refused to patent them so that everyone could benefit, and gave his Nobel prize money to his university.

Ignoring air resistance, by roughly how much does a falling object's speed increase each second near Earth's surface?

9.8 m/s is added every second; the figure is slightly larger at the poles than at the Equator, so you weigh a little more in Helsinki than in Singapore.

In the name of CERN's Large Hadron Collider, what is a hadron?

A particle made of quarks bound by the strong force, like the proton; quarks are never seen alone, because pulling one free takes so much energy that a new quark–antiquark pair forms instead.

Which British physicist is credited with discovering the electron in 1897?

J. J. Thomson showed in 1897 that cathode rays were particles over a thousand times lighter than a hydrogen ion; his son George later won a Nobel for showing electrons diffract like waves.

Which SI unit is defined as one cycle or event per second?

Hertz honours Heinrich Hertz, who proved in the 1880s that the electromagnetic waves theory had predicted were real; he died at 36 in 1894, just before others turned his waves into radio.

Which particle, proposed in 1964, did CERN's ATLAS and CMS teams announce they had finally found in July 2012?

The Higgs boson is a ripple in a field proposed in 1964 to explain how particles get their mass; Peter Higgs and François Englert shared the Nobel Prize the year after the announcement.

What random event decides the cat's fate in Schrödinger's 1935 thought experiment?

Radioactive decay: if a single atom decays, a Geiger counter trips a hammer that smashes a flask of poison. Schrödinger meant the cat that is at once dead and alive to show how absurd the idea was, not to endorse it.

Whose principle says buoyant force equals the weight of fluid displaced?

Archimedes' principle, from the Greek mathematician of Syracuse in the third century BC, explains why steel ships float: the displaced water weighs as much as the ship.

Christian Doppler first proposed his famous effect in an 1842 treatise about the coloured light of what?

Doppler's 1842 paper was titled 'On the coloured light of the binary stars'; his idea that the effect explains star colours was wrong, but the effect itself was right.

Which SI unit of pressure is named after a French mathematician who experimented with barometers?

The pascal honours Blaise Pascal, who in 1648 had a barometer carried up the Puy de Dôme to show that air pressure falls with altitude; weather maps quote hectopascals.

Albert Einstein's Nobel Prize in Physics was awarded specifically for his work on which phenomenon?

The photoelectric effect, not relativity, is what the citation names; the committee had found no worthy winner in 1921, so Einstein received that year's reserved prize a year late, in 1922.

Marie Curie won the 1903 Nobel Prize in Physics and a second Nobel in 1911 in which field?

Chemistry: the 1911 prize honoured her discovery of radium and polonium. Amid a press scandal over her private life, a Swedish Academy of Sciences member urged her to stay away; she went to Stockholm and gave her Nobel lecture anyway.

The Planck constant links a photon's energy to which property of the light?

E = hν: a photon's energy is the Planck constant times its frequency, which is why ultraviolet photons carry more punch than red ones; since 2019 h is fixed at exactly 6.62607015 × 10⁻³⁴ J·s.

Which SI unit of energy is named after an English physicist who worked in his family's brewery?

Joule honours James Prescott Joule, who let a falling weight spin a paddle in water and found that a set amount of work always gave the same heat, showing heat is a form of energy and not a fluid.

Which physicist led the first self-sustaining nuclear chain reaction at Chicago Pile-1 in 1942?

Enrico Fermi's team took Chicago Pile-1 critical on 2 December 1942 in a rackets court under the stands of Stagg Field; the success was reported by phone in an improvised code, as the Italian navigator landing in the New World.

Which particle did James Chadwick discover in 1932, earning him a Nobel Prize three years later?

The neutron was announced in a letter titled 'Possible Existence of a Neutron' after only about two weeks of experiments; having no charge, it could slip into other atoms' cores, and it was soon being used to split uranium.

In the acronym LASER, what does the letter S stand for?

Stimulated completes 'light amplification by stimulated emission of radiation'; Gordon Gould coined the acronym in a 1957 notebook, then spent some thirty years fighting to win patents on the laser.

Superconductivity was discovered in 1911 in which metal, cooled to a few degrees above absolute zero?

Heike Kamerlingh Onnes saw the resistance of mercury vanish at about 4.2 K in 1911, having liquefied helium three years earlier; he won the 1913 Nobel Prize for low-temperature work.

Léon Foucault's famous pendulum of 1851 was the first simple, direct demonstration of what?

Foucault's pendulum, hung first at the Paris Observatory and then under the Panthéon's dome in 1851, swung in a slowly turning plane, showing the rotation of the Earth directly; he repeated the feat with a gyroscope in 1852.

Which of the four fundamental forces is by far the weakest?

Gravity is weaker than the other three by dozens of orders of magnitude: a fridge magnet lifting a paperclip beats the pull of the whole planet. It still rules at large scales because it reaches any distance and always attracts.

Murray Gell-Mann took the word 'quark' from which novel?

Finnegans Wake gave Gell-Mann the spelling: he already had the sound 'kwork' in mind, and Joyce's line 'Three quarks for Muster Mark' seemed perfect because his theory then needed just three such particles.

Which quark flavours make up ordinary matter?

Up and down quarks, the two lightest flavours, are the stable ones; the four heavier flavours quickly decay into them, so they turn up only briefly in accelerators and cosmic-ray collisions.

Which observatory made the first direct detection of gravitational waves in 2015, from two colliding black holes?

LIGO's twin detectors in Louisiana and Washington state caught the signal 7 milliseconds apart; they can sense their 4 km arms changing by far less than a proton's width, and the find won a Nobel Prize two years later.

What did radio astronomers Arno Penzias and Robert Wilson discover by accident in 1964?

The cosmic microwave background, the Big Bang's leftover glow, first looked like a fault in their antenna: they evicted nesting pigeons and scrubbed out the droppings, yet the hiss stayed, and it won them the 1978 Nobel Prize.

The 1887 Michelson–Morley experiment failed to detect Earth's motion through what?

The luminiferous aether was the invisible medium that light waves were thought to travel in; the 1887 experiment found no trace of it, and Einstein's special relativity of 1905 did away with the aether altogether.

Which German physicist introduced the uncertainty principle in 1927?

Werner Heisenberg's 1927 paper used the word 'Ungenauigkeit', imprecision; the tidy modern inequality was proved by Earle Kennard later the same year.

Wolfgang Pauli postulated the neutrino in 1930 to rescue energy conservation in which process?

In beta decay the emitted electrons carried a spread of energies, as if some went missing, so Pauli proposed an invisible neutral particle; it took until 1956 to detect one.

Until 2019, water's triple point, where ice, liquid and vapour coexist, defined which SI unit?

The kelvin was defined from 1954 until 2019 by this point, 0.01 °C, because ice, water and vapour can coexist at only one temperature and pressure, which made it a reference that always comes out the same.

What is engraved on Ludwig Boltzmann's tombstone in Vienna?

His entropy formula, S = k log W, is carved above his bust, though it was Max Planck who first wrote it in that form; Boltzmann died in 1906, shortly before experiments settled that atoms are real.

The Chandrasekhar limit is the greatest mass possible for which kind of star, the final fate awaiting our Sun?

A white dwarf heavier than about 1.4 Suns cannot hold itself up and must collapse or explode; Chandrasekhar began working out the limit in 1930, aged 19, on his way from India to study at Cambridge.

The eerie blue glow in the water of a nuclear reactor pool is a classic example of which effect?

Cherenkov radiation appears when charged particles travel through water faster than light does there, a visible counterpart of a sonic boom; Pavel Cherenkov first detected it in 1934 and shared the 1958 Nobel Prize.

Which state of matter, predicted in the 1920s, was first made in 1995 near absolute zero?

A Bose–Einstein condensate formed when Eric Cornell and Carl Wieman cooled rubidium atoms to within a millionth of a degree of absolute zero in Colorado: the atoms fell into the same quantum state and behaved as one.

From 1889 until May 2019, the kilogram was defined by what?

A metal prototype cylinder of platinum-iridium, locked in a vault on the edge of Paris, defined the kilogram; its copies slowly drifted apart in mass, so since 2019 the unit has been fixed via the Planck constant instead.

Robert Millikan's 1909 oil drop experiment measured what?

Millikan and Harvey Fletcher balanced charged oil droplets between electrified plates and found every charge a multiple of one value, the charge of the electron; Millikan won the 1923 Nobel.

Which physicist adopted and popularised the term 'black hole' after a lecture in December 1967?

John Archibald Wheeler took up 'black hole' after an audience member suggested it at his December 1967 lecture, liking its 'advertising value'; he also coined 'a black hole has no hair'.

About which newly found particle, a heavy cousin of the electron, did physicist Isidor Rabi quip 'Who ordered that'?

The muon turned up in cosmic rays in 1936 and was first taken for the predicted carrier of the strong force; it proved to be a heavy electron with no such role, hence Rabi's baffled quip.

The fine-structure constant, which sets the strength of electromagnetism, is approximately equal to what?

The fine-structure constant is about 1/137, or 0.0072973525643; Arthur Eddington argued its reciprocal had to be exactly the integer 137, an idea regarded as numerology.

Henry Cavendish's 1797–98 torsion balance experiment was the first to give an accurate value for what?

The gravitational constant never appears in Cavendish's paper: he set out to weigh the world and reported Earth's density instead, the figure from which the constant was later worked out.

The Geiger–Marsden gold foil experiments led Ernest Rutherford to propose that atoms have what?

A tiny, dense nucleus was the only way to explain why a few alpha particles bounced almost straight back off the foil, which Rutherford said was like firing a 15-inch shell at tissue paper and having it come back and hit you.

Who coined the term 'Big Bang' during a BBC radio broadcast?

Fred Hoyle, champion of the rival steady-state model, used 'Big Bang' in a BBC radio talk to contrast that picture with his own; the name stuck, though he never came round to the theory it described.

The first working transistor was built in 1947 at which laboratory?

At Bell Labs in Murray Hill, New Jersey, John Bardeen and Walter Brattain pressed two gold contacts onto a germanium crystal in December 1947; they shared the 1956 Nobel with William Shockley.

Per Hawking's 1974 theory, what does his namesake radiation eventually do to a black hole?

Hawking radiation makes it evaporate: a stellar-mass black hole would take far longer than the universe's age, but a small primordial one loses mass ever faster and ends in a burst.

Which American chemist, known for his electron-dot diagrams, popularised the word 'photon' in 1926?

Gilbert N. Lewis proposed 'photon' for what he imagined as a new kind of atom that was not light itself; that idea faded, but physicists kept his word for Einstein's particle of light.

Whose equations, published in the 1860s, unified electricity, magnetism and optics?

James Clerk Maxwell calculated around 1862 that electromagnetic disturbances travel at the speed of light, and concluded that light itself must be such a wave; radio waves, found in the 1880s, proved him right.

Through which of these does sound travel fastest?

Iron carries sound about 15 times faster than air, because a stiff solid passes the vibration along far more quickly; a vacuum carries none at all, which is why space is silent.

Which sky phenomenon appears about 42° from the point directly opposite the Sun?

A rainbow's light is bent, reflected once inside each raindrop and bent again, emerging brightest at about 42°; because that arc is centred opposite the Sun, you only ever see one with the Sun behind you.

Simon Stevin dropped two lead balls from a Delft church tower in 1586, anticipating which Italian's legendary experiment?

Galileo Galilei is said to have dropped weights from the Leaning Tower of Pisa around 1590, a tale many historians doubt; Stevin's two balls, one ten times heavier, really did land together in Delft.

Who discovered radioactivity in 1896 while experimenting with uranium salts?

Henri Becquerel expected phosphorescent uranium salts to emit X-ray-like rays only after sunlight, then found they fogged photographic plates even in a dark drawer; he shared the 1903 Nobel with the Curies.

The word 'physics' ultimately derives from the Greek 'phúsis', meaning what?

Nature: Greek 'phúsis' gave Latin 'physica', the study of the natural world, and the same root gives 'physician', since the healer's art took its name from the Latin for natural science.

Which Greek philosopher, with his teacher Leucippus, argued that all matter is made of indivisible atoms?

Democritus held that nothing exists but atoms moving in a void; their name comes from the Greek for 'uncuttable', a label that stuck even after physicists learned to split them.

Ibn al-Haytham's 'Book of Optics' replaced the Greek notion of vision emanating from the eye with what?

Light rays travel from every point of an object into the eye, Ibn al-Haytham argued, and he rested the case on experiments, some using a camera obscura, rather than on abstract theory.

Which astronomer used Tycho Brahe's observations of Mars to show in 1609 that planets move in ellipses?

Johannes Kepler called the years of laborious calculation 'my war with Mars' before he gave up circles for an ellipse; his first two laws of planetary motion appeared in 1609 and the third in 1619.

The sixth-century scholar John Philoponus attacked which philosopher's physics, arguing that a thrown object carries an impressed force?

Aristotle held that a thrown object keeps moving only because the air pushes it along; Philoponus, writing in Alexandria, replied that the thrower gives it a force of its own, an idea later called impetus.

On Apollo 15, David Scott dropped a hammer alongside what object to show both fall equally fast?

A feather from a falcon hit the lunar dust at the same instant as the hammer, because there was no air to hold it back. Galileo had argued that mass makes no difference to a fall.

The crack of a bullwhip is a miniature version of which noise?

A sonic boom in miniature is what you hear when a whip cracks, because the tip of the lash outruns sound itself. A sharply snapped towel can do the same.

Which process powers the Sun, turning about four million tonnes of matter into energy every second?

Nuclear fusion in the Sun's core turns hydrogen into helium, and the mass that goes missing in the process leaves as sunlight.

In 1780, Luigi Galvani found that an electrical spark made the legs of which dead animals twitch?

Frogs made Galvani's name, and Mary Shelley later named galvanism among the ideas that stirred her to write Frankenstein.

Which quantum phenomenon did Albert Einstein dismiss as 'spooky action at a distance'?

Entanglement ties particles together so that one cannot be described without the other, however far apart they are. The 2022 Nobel Prize in Physics honoured experiments that proved it real.

Which physicist, famous for his diagrams of particle collisions, helped investigate the Challenger disaster?

Richard Feynman dunked a piece of O-ring rubber in iced water during a televised hearing, showing how cold weather had stiffened the shuttle's seals.

Which American statesman proposed flying a kite in a storm to prove that lightning is electrical?

Benjamin Franklin never meant the kite to be struck, which would probably have killed him. It only had to draw a little charge down from a storm cloud.

At which temperature do the Celsius and Fahrenheit scales show exactly the same number?

−40° is where the two scales cross, because a Fahrenheit degree is only five-ninths the size of a Celsius one and the gap between them closes as it gets colder.

Which change of state makes a block of dry ice shrink into gas without ever leaving a puddle?

Sublimation takes solid carbon dioxide straight to gas at about −78 °C, which is why dry ice can chill food without ever wetting it.

Theodore Maiman built the first working laser in 1960 around a synthetic rod of which gemstone?

Ruby in Maiman's laser was energised by a flash lamp, which he chose after a salesman claimed the biggest model could set steel wool alight.

Which optical effect makes a pencil standing in a glass of water appear to bend at the surface?

Refraction happens because light changes speed as it crosses from water into air. The same effect makes a swimming pool look shallower than it really is.

Which property of matter, named from the Latin for 'idle', keeps a moving object moving unless a force acts?

Inertia got its name from Johannes Kepler, who took it from the Latin for idleness, although he meant something slightly different by it than physicists do now.

Which SI unit of temperature, named after a Belfast-born physicist, counts upward from absolute zero?

Kelvin honours Lord Kelvin, whose title came from the river that flows past his old laboratory at the University of Glasgow.

In Albert Einstein's famous equation E = mc², what does the letter c stand for?

The speed of light is such a large number that, once squared, it means a tiny amount of mass corresponds to an enormous amount of energy.

Which form of energy does a moving car have, quadrupling whenever the car's speed doubles?

Kinetic energy rises with the square of speed, so a car travelling twice as fast needs four times the distance to stop under the same braking force.

Which colour of visible light has the longest wavelength and is bent least by a glass prism?

Red sits at the long end of the visible spectrum, at roughly 625 to 740 nanometres, so a prism turns it through the smallest angle and violet through the largest.

Which physicist directed the Los Alamos laboratory that built the first atomic bombs in the Second World War?

Robert Oppenheimer was appointed in 1943, yet a 1954 hearing stripped him of his security clearance, a ruling the US government only struck down in 2022.

Which Serbian-American inventor's 1887 induction motor helped alternating current win the 'war of the currents'?

Nikola Tesla fell into relative obscurity after his death, until in 1960 the SI unit of magnetic flux density was named the tesla in his honour.

Which sky display, seen mostly near the poles, appears when charged particles from the Sun strike Earth's upper air?

An aurora is named after the Roman goddess of the dawn, and the same glow has been seen on Jupiter, Saturn, Uranus and Neptune.

Which radioactive isotope, with a half-life of about 5,730 years, lets archaeologists date ancient bones and wood?

Carbon-14 stops being topped up when a plant or animal dies, so the amount left works as a clock, reliable back to roughly 50,000 years.

What name is given to the steady top speed, about 200 km/h belly-down, that a falling skydiver settles at?

Terminal velocity arrives when air resistance grows to match the skydiver's weight. Speed skydivers who fall head-down nearly triple it, reaching about 150 metres per second.

Which form of heat transfer drives sea breezes and makes warm air rise from a radiator to the ceiling?

Convection works because warmed fluid becomes less dense and floats upward while cooler, denser fluid sinks to take its place, which sets up a circulating loop.

Which effect lets a loud note shatter a wine glass when it matches the tone the glass itself rings at?

Resonance makes each sound wave push the glass at just the right moment, so the vibration builds until the glass fractures. Doing it reliably takes practice and a carefully chosen glass.

Which radioactive element, found in the uranium ore pitchblende in 1898, did Marie Curie name after her homeland?

Polonium was named for a country missing from the map: in 1898 Poland was split between Russia, Germany and Austria-Hungary and did not exist as an independent state.

Which former bookbinder's apprentice discovered electromagnetic induction, the principle behind the electric generator?

Michael Faraday had little formal education and taught himself from the books he bound, yet he became one of the most influential scientists in history.

Which unit for sound levels grew out of 1920s efforts to measure signal loss in telephone lines?

Decibel readings replaced an older measure called 'miles of standard cable', which rated how much a telephone signal faded along a line.

Which metal has the highest electrical conductivity of all, beating even copper?

Silver is too costly for household wiring, but it is plated onto radio components, where rapidly alternating currents flow along a conductor's surface.

Which circuit layout makes every bulb in a string of old fairy lights go dark when a single bulb burns out?

Series wiring puts every bulb in one continuous loop, so a single failure breaks the path for all of them. Wired in parallel, each bulb gets a loop of its own.

Which part of the electromagnetic spectrum, discovered by Paul Villard in 1900, has the shortest wavelengths of all?

Gamma rays got their name three years later from Ernest Rutherford, who simply carried on the Greek-letter scheme he had started with two weaker kinds of ray.

Which term, coined by Wolfgang Rindler in the 1950s, names the boundary of a black hole that nothing can recross?

Event horizon is the modern name, but John Michell had the idea back in 1784, proposing bodies so massive that even light could not escape them.

Which effect lets water striders stand on a pond and pulls falling raindrops into spheres?

Surface tension can even hold up a steel razor blade, which is far denser than water, so long as the blade rests on the surface without breaking through it.

What makes hurricanes spin anticlockwise north of the equator and clockwise south of it?

Coriolis effect does not decide which way a sink or toilet drains, whatever the popular story says. At that scale the shape of the bowl matters far more.

Which effect of relativity was confirmed in 1971 by flying atomic clocks around the world on commercial airliners?

Time dilation showed up when the clocks came home: after one lap of the planet eastward and one westward, they no longer agreed with the clocks left at the US Naval Observatory.

Alessandro Volta's 1800 stack of zinc and copper discs was the first true example of which device?

Electric battery power began with this pile, the first source of a continuous current. Volta separated each pair of discs with cloth or card soaked in brine.

Which Austrian physicist, who photographed shock waves around bullets, gave his name to multiples of the speed of sound?

Ernst Mach and his son Ludwig used schlieren photography to capture the invisible cone of compressed air that trails from a supersonic projectile.

Which state of matter, seen in lightning and neon signs, makes up most of the ordinary matter in the universe?

Plasma got its name in 1928 from Irving Langmuir, whose colleagues recalled that the glowing gas reminded him of the way blood plasma carries its corpuscles.

Which law of stretched springs was first published in 1676 as the Latin anagram 'ceiiinosssttuv'?

Hooke's law stayed hidden in the anagram for two years, until its author printed the solution: 'ut tensio, sic vis', or 'as the extension, so the force'.

Whose double-slit experiment, first described in 1801, made the case that light behaves as a wave?

Thomas Young was a polymath who also helped decipher the Rosetta Stone, working on its demotic text before falling into a long rivalry with Jean-François Champollion.

Whose 1913 model of the atom let electrons jump between fixed orbits, giving off light as they did?

Niels Bohr went on to found the Copenhagen institute that now bears his name, and the synthetic element bohrium honours him too.

Which unseen material, inferred from how fast galaxies rotate, outweighs the stars, gas and planets about five to one?

Dark matter has never been seen directly, because it neither emits nor absorbs light. It shows itself only through its pull on the stars and galaxies around it.

Which famously taciturn British physicist wrote the 1928 equation that predicted the existence of antimatter?

Paul Dirac spoke so rarely that his Cambridge colleagues jokingly defined a unit, the 'dirac', as one word per hour.

Which Austrian-born physicist helped explain nuclear fission, yet was left out of the Nobel Prize given to Otto Hahn?

Lise Meitner had fled Nazi Germany only months earlier. She worked out the physics on a snowy walk in Sweden that Christmas with her nephew, Otto Frisch.

Which astronomer led a 1919 eclipse expedition to the island of Príncipe that showed starlight bending around the Sun?

Arthur Eddington was a Quaker pacifist, and his exemption from wartime military service was granted on condition that he kept preparing for the expedition.

Which scientist showed in 1820 that an electric current deflects a compass needle, linking electricity with magnetism?

Hans Christian Ørsted had predicted such a link as early as 1813, and his result set André-Marie Ampère to work on the mathematics of the force between current-carrying wires.

Which mathematician, lecturing unpaid under David Hilbert's name, proved that each conservation law reflects a symmetry?

Emmy Noether proved it while helping Hilbert make sense of general relativity. Albert Einstein later called her the most significant creative mathematical genius since women's higher education began.

Which one-atom-thick material did two Manchester physicists first isolate in 2004 using ordinary sticky tape?

Graphene was first peeled from a piece of graphite with adhesive tape, which split the flakes thinner and thinner until a single layer was left. The work won the 2010 Nobel Prize in Physics.

Which phenomenon makes water droplets skitter across a very hot pan, riding on a cushion of their own vapour?

Thanks to the Leidenfrost effect, a droplet lasts longer on a scorching pan than on a merely hot one, because its layer of vapour insulates it from the heat below.

Otto von Guericke's copper hemispheres, which teams of horses could not pull apart, are named after which German city?

Magdeburg was the city Guericke served as mayor. Once he had pumped the air out of the sphere, the pressure of the atmosphere alone clamped its two halves together.

Which jittery movement of pollen particles in water did Albert Einstein explain in 1905 as bombardment by molecules?

Brownian motion is named after the botanist Robert Brown, who described it in 1827. Einstein's account of it became convincing evidence that atoms and molecules really exist.

Which seemingly solid substance drips about once a decade from a University of Queensland funnel set up in 1927?

Pitch looks solid but is really a liquid about 230 billion times more viscous than water, which is exactly what the experiment was set up to show students.