100 Fun Facts About Heat

What is the SI unit of measurement for heat?

Joule is named after James Joule, who let a falling weight spin a paddle wheel in a barrel of water and showed that the stirring alone warmed it: work turns into heat.

Which American statesman invented a metal-lined fireplace in 1742 to give more heat with less smoke?

Benjamin Franklin never patented his stove, or any other invention: having gained so much from other people's ideas, he said, we should be glad to share our own freely.

Which glass cookware brand was launched in 1915 after a physicist's wife tried baking in a sawn-off battery jar?

Pyrex grew out of glass made for railway lanterns: physicist Jesse Littleton took home a sawn-off battery jar of it, and his wife Bessie baked in it without the glass cracking.

The word 'calorie' comes from 'calor', meaning 'heat' in which ancient language?

Latin calor gave the French chemist Nicolas Clément a name for the unit of heat he defined for his students in lectures of the early 1820s, while studying the fuel efficiency of steam engines.

Which property of water makes the sea warm more slowly than land?

Specific heat capacity is unusually high for water, so oceans soak up summer heat and give it back slowly, which is why coastal cities see smaller swings of temperature than inland ones.

Which heat-transfer mechanism works by warmer, less dense fluid rising and cooler fluid sinking?

Convection also builds thunderstorms: air warmed by sunlit ground rises and cools until its water vapour condenses into towering storm clouds.

Which heat-transfer mechanism passes heat through a material, or between objects that are touching?

Conduction is why a metal spoon feels colder than a wooden one at the same temperature: the metal carries heat away from your skin far faster.

Which word, also used for filament light bulbs, describes the glow an object gives off because it is hot?

Incandescence wastes most of a filament bulb's power as heat rather than light, which is why LED lamps, using up to 90% less energy, have replaced them.

Which gemstone carries heat away faster than any metal, a trait jewellers use to tell it from fakes?

Diamond pulls heat away so quickly that the warm tip of a jeweller's probe cools the instant it touches a real stone, while most imitations barely take any heat at all.

Which Scottish chemist introduced the term 'latent heat' for the heat that melting ice absorbs without getting warmer?

Joseph Black called the heat 'latent', meaning hidden: ice in a warm room went on soaking up heat for hours while a thermometer in it stayed at freezing.

What is absolute zero on the Celsius scale?

−273.15 °C was first glimpsed in chilled gases: they shrink so steadily as they cool that scientists could work out the temperature at which a gas would, in theory, shrink to nothing.

Which US national park has the world's largest concentration of geysers, heated by magma lying beneath it?

Yellowstone has more than 10,000 hydrothermal features, over 500 of them geysers: rain seeps deep into the rock, is superheated by magma and rises back to the surface.

Which scales set their zero points at absolute zero by definition?

Kelvin and Rankine both count up from absolute zero: the Scottish engineer William Rankine set up his scale in 1859 with Fahrenheit-sized degrees, for those who did their sums in Fahrenheit.

Greece's Thermopylae means 'hot gates', after which natural feature there?

Sulphur springs still run hot at Thermopylae, the narrow coastal pass where about 7,000 Greeks under the Spartan king Leonidas held back a far larger Persian army in 480 BC.

In 1954 the kelvin was defined by fixing 273.16 K as the temperature of what?

Triple point of water is the one temperature and pressure at which ice, liquid water and vapour all exist together, so any lab can recreate it exactly inside a sealed glass cell.

The hot 'dog days' of summer are named after which star?

Sirius, the Dog Star, returned to the dawn sky in the hottest weeks of the year, and the ancient Greeks and Romans believed the brilliant star was adding its own heat to the Sun's.

Anders Celsius's original 1742 scale set which value at the boiling point of water?

0 marked boiling and 100 marked freezing on Celsius's scale, so a hotter day gave a lower reading; the two points were swapped into their modern order after his death in 1744.

Which German chemist gave his name to the adjustable gas burner used in school science labs?

Robert Bunsen introduced the burner in 1855: mixing air into the gas before it burns gives a much hotter flame, the idea later built into the gas-stove burner.

What was the profession of Anders Celsius, after whom the scale is named?

Astronomer Anders Celsius built Uppsala's observatory and joined a 1736 expedition to Lapland whose measurements confirmed that the Earth is slightly flattened at the poles.

Fahrenheit set 0 °F with a freezing mix of ice, water and sal ammoniac, the old name for which salt?

Ammonium chloride, ice and water settle by themselves at one steady low temperature, which gave Fahrenheit a zero that any instrument maker could reproduce at the bench.

Which NASA spacecraft flies through the Sun's atmosphere?

Parker Solar Probe flies behind a carbon shield whose Sun-facing side reaches about 1,400 °C, while the spacecraft in its shadow sits at about 30 °C, a warm summer's day.

Fahrenheit fixed 96 degrees on his original scale as the temperature of what?

A healthy human was Fahrenheit's upper marker: he first called body temperature 90 degrees and then 96; later fine-tuning of his scale is why normal body temperature now reads 98.6 instead.

In 1714 Daniel Gabriel Fahrenheit built a reliable thermometer using which liquid?

Mercury made Fahrenheit's thermometers the standard for almost three centuries, but it is a potent neurotoxin, and in 2011 America's standards lab stopped calibrating mercury thermometers altogether.

Which Italian scientist is generally credited with the first thermometer, an upturned glass flask?

Galileo Galilei is said to have built it, though others have a claim too: air trapped in the flask swelled and shrank with the temperature and moved the water in its neck, but with no scale it showed changes, not degrees.

A bimetallic strip bends as it warms because its two metals differ in which property?

Thermal expansion differs between the two bonded metals, so one side lengthens more and the strip curls; that curl once switched home thermostats on and off.

Which actor played detective Virgil Tibbs in the 1967 crime drama In the Heat of the Night?

Sidney Poitier's Virgil Tibbs is picked up as a murder suspect in a Mississippi town, turns out to be a top homicide detective from Philadelphia, and stays to help solve the case.

Who observed heat from boring cannon in Munich and reported on it in 1798?

Count Rumford, born Benjamin Thompson in Massachusetts, bored a cannon barrel under water with a blunt drill and brought the water to the boil by friction alone, heat that never seemed to run out.

Which chemist introduced a version of the caloric theory, treating heat as a fluid?

Antoine Lavoisier listed caloric, a weightless substance of heat, among his 33 chemical elements, as though warmth were a material like any metal or gas.

Which Munich park was created from 1789 at the urging of the physicist Benjamin Thompson, an adviser to Bavaria's ruler?

Englischer Garten was decreed in 1789 to be 'not just for one section of society but for the whole population', and it is still one of the largest inner-city parks in the world.

Who invented the vacuum flask, or thermos, in 1892?

James Dewar built the flask to keep liquefied gases cold in his laboratory; it reached picnic baskets only after a German firm began selling it under the name Thermos in 1904.

As of 2025, which place holds the official record for Earth's highest air temperature?

Death Valley's Furnace Creek reached 56.7 °C (134 °F) on 10 July 1913; the valley is a long, narrow basin below sea level, walled in by steep mountains that trap the heat.

Which North African country's 1922 reading stood as the world heat record for 90 years before being struck off?

Libya's reading at El Azizia stood until 2012, when an international panel ruled that an inexperienced observer had probably misread his instrument, by as much as 7 °C.

Lightning briefly heats the air to about five times the temperature of what?

The Sun's surface is about 5,500 °C, but lightning heats the air in its path to roughly 30,000 °C; the air expands so fast that it sends out the sound wave we hear as thunder.

What is the temperature at the centre of the Sun's core?

15 million K is hot enough for nuclear fusion, and the outward pressure that creates is what holds up the Sun's enormous mass against its own gravity.

Engineer Percy Spencer thought of the microwave oven when a magnetron melted what in his pocket?

A candy bar is said to have melted in Spencer's pocket, so he held a bag of popcorn kernels up to the magnetron next and watched them burst into the first microwave popcorn.

What was the name of Raytheon's first commercial microwave oven, sold from 1947?

Radarange stood about six feet tall and weighed some 750 pounds, so the first ones went to restaurants and hotels; ovens small enough for a home kitchen took about another 20 years.

The effect in which a water droplet skitters across a very hot pan is named after which German doctor?

Johann Leidenfrost described how the droplet floats on a cushion of its own vapour, which insulates it so well that it lasts far longer than it would on a cooler pan.

Water boils at around 70 °C on the summit of which mountain?

Mount Everest's summit has only about a third of the air pressure found at sea level, and the less air there is pressing down on water, the lower the temperature at which it boils.

Which illness can follow heat exhaustion if the body's temperature keeps climbing?

Heatstroke is a medical emergency: unlike heat exhaustion, which usually eases within half an hour of cooling down, it can bring confusion, seizures and loss of consciousness.

The heat index combines air temperature with which other measurement?

Relative humidity is the other ingredient, and the index assumes you are standing in shade and a light wind, so direct sunshine feels hotter still than the figure given.

Which French mathematician proposed in the 1820s that Earth's atmosphere traps heat, the idea now called the greenhouse effect?

Joseph Fourier asked why the night side of the Earth does not simply freeze, and reasoned that the atmosphere lets sunlight in to warm the ground while holding back the heat trying to escape.

Western saunas originated in which country?

Finland has roughly three million saunas for under six million people, and Finns were once born in them, since a sauna was the cleanest room with hot water to hand.

In a sauna, the steam called löyly comes from throwing water onto what?

Hot stones heated by the stove flash the water into steam, and the wave of steam makes the room feel far hotter than before, though the stove itself is no hotter.

Which NBA star said in 2010 that he was taking his 'talents to South Beach' to join the Miami Heat?

LeBron James broke the news in a live ESPN special called The Decision, then won his first two NBA championships with the Heat, in 2012 and 2013.

Which law ties a body's radiated heat to the fourth power of its absolute temperature?

Stefan–Boltzmann law means that doubling a body's absolute temperature makes it radiate sixteen times as much power.

What did the 2019 revision of the SI fix to define the kelvin?

Boltzmann constant is the fixed number that links temperature to energy, so since 2019 the kelvin has rested on a constant of nature instead of on any physical object or substance.

Which type of cooktop heats the pan directly with a magnetic field?

Induction hobs turn the pan itself into the heater: a coil under the glass sets up a rapidly changing magnetic field that drives electric currents through the base of the cookware.

Heat from the Sun crosses empty space as what kind of wave?

Electromagnetic waves need nothing to travel through, unlike sound, and about half of the Sun's energy reaching the ground is infrared, which we feel as warmth but cannot see.

Which fibrous mineral, once prized as fireproof insulation, is now banned in many countries for causing lung disease?

Asbestos resists heat so well that it was packed into buildings as insulation and fire retardant, but its fibres, once breathed in, can cause lung disease that takes many years to show.

In which present-day Polish city was the thermometer maker Daniel Fahrenheit born in 1686?

Gdańsk, then called Danzig, lost him early: Fahrenheit left as a teenager and spent most of his life in the Netherlands, where he made his name building precision thermometers.

Ray Bradbury's Fahrenheit 451 is named for the temperature at which what is said to catch fire?

Paper was the answer Bradbury got when he phoned the Los Angeles fire department to ask. Later studies put its ignition point anywhere from 424 to 475 °F, depending on the type.

Which metal landmark's summit leans up to 18 cm away from the Sun as its sunlit side heats up?

The Eiffel Tower bends because the metal facing the Sun warms and lengthens more than the shaded side. Over a clear day the top traces a rough circle about 15 cm across.

Which scale, devised by an American pharmacist in 1912, rates the heat of chilli peppers?

Scoville had a panel of five tasters sip pepper extract diluted in sugar water until most could no longer feel the burn. A jalapeño scores 2,500 to 10,000 on his scale.

Which volcanic island nation heats at least nine in ten homes with hot water from underground?

Iceland pipes naturally hot groundwater straight into its homes, and the same supply warms outdoor swimming pools and keeps streets and pavements free of snow.

Which supersonic airliner stretched up to 30 cm as its fuselage heated in flight?

Concorde grew so much that a gap opened on the flight deck beside the engineer's console. On some farewell flights, engineers wedged their caps into it before the airframe cooled and shrank.

The 1995 film Heat was sold on the first shared scene of which two Godfather Part II stars?

Pacino and De Niro had co-starred in that 1974 film without sharing a single scene. Their meeting in a diner in Heat was shot with minimal rehearsal to keep it spontaneous.

Which metal, long used for light-bulb filaments, has the highest melting point of all metals?

Tungsten stays solid up to 3,422 °C, hotter than any other metal can stand. Its name is Swedish for 'heavy stone', yet its chemical symbol is W, from the rival name wolfram.

Venus is the hottest planet, at about 464 °C, because its air is 96.5% which heat-trapping gas?

Carbon dioxide makes up nearly all the air on Venus, and the blanket is so thick that pressure at the surface is 92 times Earth's at sea level.

Which optical illusion makes a hot road look wet as light bends through warm air above the tarmac?

A mirage forms because tarmac or sand can be more than 10 °C hotter than the air a metre above. Light from the sky bends through that layer, so the eye sees what looks like a puddle.

The Montgolfier brothers' hot-air balloon of 1783 carried a duck, a rooster and which other animal?

A sheep called Montauciel, or 'Climb-to-the-sky', was chosen as a fair stand-in for human physiology. The king had first proposed sending up two convicted criminals.

A thermometer in a gas is really tracking the average of which form of energy in its molecules?

Kinetic energy is the energy of motion, so a hotter gas is simply one whose molecules move faster. Cool the gas and they slow, which is why there is a coldest possible temperature.

Which law of thermodynamics says heat flows by itself only from hotter bodies to colder ones?

The second law explains why a hot drink always cools to match the room, never the reverse. A refrigerator can push heat from cold to hot, but only because a motor forces it.

Two objects at the same temperature, with no net heat flowing between them, are in what state?

Thermal equilibrium is what makes thermometers possible: one reads true only once it has settled to the temperature of what it touches. Physicists call the principle the zeroth law of thermodynamics.

Which measure, used to rate air conditioners, is the heat that warms a pound of water by 1 °F?

The British thermal unit is used mainly in North America, where one 'ton' of air conditioning means 12,000 of them an hour, or about 3.5 kW.

The Calorie on American food labels equals how many of the small calories used in chemistry?

1,000 small calories make one food Calorie, properly called a kilocalorie. The capital C for the large unit was proposed by the French chemist Marcellin Berthelot in 1879.

Which name is given to a solid turning straight into gas, as dry ice does at room temperature?

Sublimation is why dry ice chills without leaving a puddle: at normal pressure it has no liquid state at all. Freeze-drying uses the same jump to pull frozen water out of food.

Sweating cools the human body because heat leaves the skin through which process?

Evaporation draws heat from the skin as sweat turns to vapour. Few other mammals cool this way; horses do, with a soapy protein called latherin that spreads sweat through the coat.

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

−40 is the single point where the two scales cross, because a Fahrenheit degree is only five-ninths the size of a Celsius one. Below it, Fahrenheit readings are the lower of the two.

Which older name for the Celsius scale was dropped in 1948 because it also named a unit of angle?

Centigrade, from the Latin for 'a hundred steps', was also the word in some languages for a hundredth of a gradian. The 1948 change honoured the scale's Swedish inventor instead.

The fire triangle lists heat and fuel as two things every fire needs; which gas is the third?

Oxygen is the side of the triangle a fire blanket attacks, by sealing off the air. Fire scientists later added a fourth requirement, the chemical chain reaction, making the triangle a tetrahedron.

Among stars, which colour signals the hottest surface?

Blue stars of type O are the hottest class of all, and so massive that they burn through their hydrogen fuel very quickly and are the first to leave the main sequence.

Which outer layer of the Sun, seen during a total eclipse, runs at more than a million degrees?

The corona is hundreds of times hotter than the Sun's surface, which sits at only about 5,800 K. Why the faint outer halo should be so hot is known as the coronal heating problem.

Which fourth state of matter, found in lightning and neon signs, forms when a gas becomes ionised?

Plasma is rare on Earth, yet stars are almost pure balls of it. The American chemist Irving Langmuir gave ionised gas the name in 1928, by analogy with the plasma of blood.

Which term describes a chemical reaction, such as burning, that releases heat to its surroundings?

Exothermic comes from the Greek for 'outward' and 'thermal'. The opposite kind of reaction absorbs heat instead, which is how a first-aid cold pack chills its surroundings.

Which electric device warms a house by collecting warmth from cold outdoor air?

A heat pump moves warmth rather than making it, so it typically delivers three or four times more thermal energy than the electricity it uses.

Which sealed pot cooks faster by trapping steam to raise water's boiling point to about 120 °C?

The pressure cooker descends from the 'steam digester' that French physicist Denis Papin invented in 1679 to cut cooking times. At full pressure the water inside boils near 121 °C rather than 100.

Which part of the human brain is the body's thermostat, switching on sweating to cool the blood?

The hypothalamus sets the body's target temperature, and a fever is simply that setting turned up. A raised temperature from any other cause is classed as hyperthermia instead.

Which compound makes chilli peppers burn by triggering the same nerve receptor as scalding heat?

Capsaicin fools a receptor that normally warns of excessive heat, yet birds cannot feel it at all. That suits the plant, because birds swallow the seeds whole and spread them.

Glider pilots look for which cloud type, the visible cap on a rising column of sun-warmed air?

Cumulus clouds form where a thermal, a rising bubble of warm air, cools enough for its water vapour to condense into droplets. The Sun warms the ground, and the ground warms the air above it.

Which measure, first worked out in Antarctica, describes how cold moving air feels on bare skin?

Wind chill was first put into formulas and tables by Paul Siple and Charles Passel, working in the Antarctic before World War II. Moving air feels colder because it strips heat from skin faster.

Which gas, liquid below about −196 °C, is used by doctors to freeze off warts?

Nitrogen forms about 78% of the air, so there is plenty to liquefy. The liquid boils the instant it meets anything warmer, wrapping the object in an insulating layer of gas bubbles.

Which gas, liquid only within five degrees of absolute zero, cools the magnets of MRI scanners?

Helium has the lowest boiling point of any element, and chilling the superconducting magnets in MRI scanners is the largest single use of the liquid.

Which metal melts at just under 30 °C, so a solid lump turns liquid when held in a warm hand?

Gallium melts at 29.76 °C but does not boil until about 2,400 °C, one of the largest liquid ranges of any metal. Its melting point is steady enough to serve as a temperature reference.

Which German-born musician found infrared rays in 1800 with a thermometer placed beyond red light?

William Herschel passed sunlight through a prism to take the temperature of each colour, then measured just beyond the red end. He is better known for discovering the planet Uranus.

Which Scottish engineer's separate condenser stopped steam engines wasting most of their heat?

James Watt showed that about three-quarters of the steam's energy went on reheating a cylinder that was chilled on every cycle. Condensing the steam in a separate chamber kept the cylinder hot.

Whose law of cooling says a body loses heat in proportion to how much hotter it is than the room?

Isaac Newton published his work on cooling anonymously in 1701, under a Latin title meaning 'a scale of the degrees of heat'. His rule is why a hot drink cools quickly at first, then ever more slowly.

Which measure of disorder, named in 1865 to echo 'energy', never falls in an isolated system?

Entropy was coined from a Greek word for 'transformation'. The German physicist who named it defined it as a tiny amount of heat divided by the temperature at which it flows.

Which fire-like substance did early chemists wrongly believe escaped from anything that burned?

Phlogiston grew out of the ideas of the 17th-century German alchemist Johann Joachim Becher. The theory unravelled when experiments showed that some metals gain mass as they burn, though they were supposed to be losing it.

Which director, executive producer of TV's Miami Vice, wrote and directed the 1995 crime film Heat?

Michael Mann wrote the script in 1979 and first filmed it as a television pilot, shot in nineteen days and aired in 1989 as L.A. Takedown when no series followed.

Lord Kelvin took his title from a river beside the university of which Scottish city?

Glasgow was where the Belfast-born William Thomson was a professor for 53 years. Made a baron in 1892, he took the name of the River Kelvin, which runs by the university grounds.

Which French engineer's 1824 book on the motive power of fire made him the 'father of thermodynamics'?

Sadi Carnot paid for the printing of all 600 copies himself, and the short book was the only work he ever published. He died of cholera at 36, in relative obscurity.

On which French scale, once common in Germany and Russia, does water boil at just 80 degrees?

The Réaumur scale was once so widespread that it is referenced in the works of Tolstoy, Dostoevsky and Flaubert. Its 80 steps also earned it the name 'octogesimal division'.

Which Dane, first to show that light has a finite speed, built a temperature scale that inspired Fahrenheit?

Ole Rømer was visited in Copenhagen in 1708 by the young Fahrenheit, who left with a keen interest in improving thermometers. Rømer's own scale was nearly lost until his notebook was published in 1910.

Which German physician's 1868 book set normal human body temperature at 37 °C, or 98.6 °F?

Carl Wunderlich's book put temperature charts into widespread hospital use. Modern measurements make the true average a little lower than his figure, at about 36.8 °C.

Which imaginary being of 1867 sorts fast and slow gas molecules to make heat flow from cold to hot?

Maxwell's demon first appeared in a letter that James Clerk Maxwell wrote in 1867. The word 'demon' was not his own: Lord Kelvin first used it for the idea in the journal Nature in 1874.

Which effect, named after a schoolboy making ice cream, has hot liquid freezing faster than cold?

The Mpemba effect is named after Erasto Mpemba of Tanzania, who noticed in a 1963 cookery class that his hot mixture froze before a cold one. Water experiments since have given mixed results.

Which nebula, colder than the faint afterglow of the Big Bang, is the coldest natural place known?

The Boomerang Nebula owes its chill to gas streaming out of a dying star at about 164 km/s. The gas expands so rapidly that it cools below the background temperature of space.

The 1995 film Heat grew from a real detective's pursuit of thief Neil McCauley in which US city?

Chicago detective Chuck Adamson tracked the real McCauley down in 1964. The two men once met for coffee, and the film's famous conversation between cop and robber is based on what they said.

Above which temperature, named after a French physicist, does iron lose its permanent magnetism?

The Curie point honours Pierre Curie, who used strong magnets and precision balances in 1895 to show that magnetism is lost at a critical temperature.

Which mixture of aluminium powder and iron oxide burns fiercely enough to weld railway tracks?

Thermite was first used commercially to weld tram tracks in Essen in 1899. The mixture needs no outside air to burn, and the reaction throws off globules of molten iron.