154 Fun Facts About 9th Grade

What do we call a whole number greater than 1 that has more than two factors?

Composite numbers can be made by multiplying smaller whole numbers, as 12 = 3 × 4; the number 1 is neither prime nor composite, since its only factor is itself.

Slope is defined as the ratio of which two things?

Rise to run: slope is the change in y divided by the change in x between two points on a line, so a level line has slope zero.

What name is given to the highest or lowest point of a parabola, where the curve turns?

The vertex is where a parabola turns and crosses its axis of symmetry, so the curve on one side is a mirror image of the other.

In ax² + bx + c = 0, what is the name given to c?

c is the constant coefficient, or constant term: a is the quadratic coefficient and b the linear coefficient, and if a were zero the equation would just be linear.

Which method is used to derive the quadratic formula?

Completing the square: you rewrite ax² + bx + c = 0 so the left side is a perfect square equal to a constant, then take the square root and solve for x.

The Pythagorean theorem relates the three sides of which kind of triangle?

Right triangles alone obey the rule, and Greece was not the only place to find it: India's Baudhayana Sulba-sutra, written between 800 and 400 BC, states it too.

What is the longest side of a triangle with a 90-degree angle called?

The hypotenuse is always the longest side; its name is Greek for 'stretching under', because it stretches beneath the triangle's 90-degree angle.

Besides geometry, Pythagoras is traditionally credited with finding the mathematical ratios behind which art?

Music: legend has Pythagoras hearing blacksmiths' hammers ring in harmony, and his followers taught that pleasing intervals come from simple ratios such as 2 to 1.

Which civilisation used the Pythagorean rule over a thousand years before Pythagoras?

Babylonians were listing Pythagorean triples on the clay tablet Plimpton 322 around 1800 BC, so the rule carries the name of a Greek born over a millennium after it was in use.

The word 'algebra' comes from which language?

Arabic gave us al-jabr, a word that named both a step in solving equations and, among medieval doctors, the setting of broken bones.

Which 9th-century scholar's treatise on solving equations gave algebra its name?

Al-Khwarizmi's treatise of around 820 gave algebra its name; his own name, Latinised as Algoritmi, became the word algorithm.

In the order-of-operations mnemonic PEMDAS, what does the E stand for?

Exponents come straight after parentheses, which is why 2 × 3² equals 18 rather than 36: the squaring is done before the multiplying.

Who proved around 300 BC that there are infinitely many primes?

Euclid's proof in the Elements shows no finite list of primes is complete: multiply them all together, add 1, and the result has a prime factor missing from the list.

What is the only even prime number?

Every other even number is divisible by 2, so every other prime is odd.

Which ancient Greek, who also measured the Earth's circumference, devised the 'sieve' for finding prime numbers?

The sieve of Eratosthenes, devised in the 3rd century BC, lists primes by writing out the numbers and crossing off every multiple of each prime you find.

On a graph, the solutions of an equation such as y = 2x + 1 form what shape?

A straight line: y climbs by the same amount for every step along x, so the points never curve, which is why equations like this are called linear.

Which form of algebra, taught in schools, uses variables to stand for unspecified values?

Elementary algebra swaps the fixed numbers of arithmetic for letters such as x, so a single rule can be written once and cover every case.

What name is given to the proteins that speed up chemical reactions inside living things?

Enzymes lower the energy a reaction needs to get started and come out of it unchanged, so one enzyme molecule can do the same job again and again.

Who first described cells in 1665 after studying a thin slice of cork under a microscope?

Robert Hooke saw a honeycomb of tiny cavities in the cork and called them cells in his 1665 book Micrographia, the first use of the word for a unit of life.

Which organelles provide energy for cell functions?

Mitochondria are the cell's powerhouses, where cellular respiration breaks down glucose to release usable energy; plant cells have mitochondria as well as chloroplasts.

Bacteria and archaea belong to which broad group of single-celled organisms?

Prokaryotes keep their DNA loose in the cell with no membrane around it; archaea look so like bacteria that they were classed with them until Carl Woese's gene studies split them apart in 1977.

Which organelle stores an animal cell's chromosomes?

The nucleus keeps the chromosomes behind a double membrane whose pores control what passes in and out, letting copied genetic messages leave while the DNA stays put.

What gas do plants release as a by-product of photosynthesis?

The oxygen comes from splitting water molecules in the light-dependent reactions, not from the carbon dioxide the plant takes in.

Which plant pigment absorbs red and blue light and reflects green?

Chlorophyll reflects green light, so leaves look green; when it breaks down in autumn, the yellow and orange pigments it was masking finally show through.

What is the name of the light-independent reactions that build sugars in plants?

The Calvin cycle uses the energy carriers made in the light-dependent stage to fix carbon dioxide into three-carbon sugars, which the plant then builds into glucose.

In which part of the chloroplast do the light-dependent reactions of photosynthesis occur?

Thylakoid membranes, stacked like coins inside the chloroplast, trap light and use its energy to split water and charge the energy-carrying molecules that power sugar-making.

What molecule stores the chemical energy produced by cellular respiration?

ATP, adenosine triphosphate, stores the energy released by respiration in its phosphate bonds; breaking off the third phosphate powers most of the work a cell does.

Which first stage of cellular respiration takes place in the cell's cytosol?

Glycolysis, literally 'sugar splitting', breaks one glucose into two pyruvate molecules in the cytosol and works with or without oxygen.

Which type of cell division halves the chromosome number to produce eggs and sperm?

Meiosis copies the DNA once but divides twice, so its four cells each carry half the usual chromosomes; fertilisation then restores the full set.

Which mitosis stage sees daughter chromosomes pulled toward opposite ends of the cell?

Anaphase starts when the link holding each pair of copies is cut and the spindle fibres abruptly shorten, hauling one copy to each end so both new cells get a full set.

Which word describes a tumour that does not spread to other parts of the body?

Benign tumours do not invade nearby tissue, and once removed they usually do not grow back; even so, some can be life-threatening, such as those in the brain.

Which process follows mitosis, physically splitting the parent cell into two?

Cytokinesis finishes what mitosis starts: an animal cell is pinched in two by a tightening ring of protein fibres, while a plant cell builds a new wall across its middle.

In DNA, adenine always pairs with which base?

Thymine pairs only with adenine, and guanine only with cytosine, so each strand of DNA can serve as a template for rebuilding its partner when a cell copies its genes.

Which name describes the structure of DNA that Watson and Crick proposed in 1953?

Double helix: two strands wind around each other like a twisted ladder; earlier that year Linus Pauling had proposed a three-stranded model of DNA, which proved wrong.

What sugar is found in each nucleotide of DNA?

Deoxyribose has one oxygen atom fewer than ribose, the sugar in RNA; without that reactive group DNA is the more chemically stable molecule, a good fit for storing genes.

Which plant did Gregor Mendel use for his experiments on heredity?

Pea plants suited Mendel because they come in many distinct true-breeding varieties and their pollination is easy to control, so he could decide exactly which plants crossed.

Which diagram, named after a British geneticist, predicts the ratios Mendel found among offspring?

Punnett square: Reginald Punnett's grid lines up each parent's possible gametes like a multiplication table, so every box shows one combination the offspring could inherit.

Which pair of terms did Mendel coin for traits that appear in hybrids and traits that stay hidden?

Dominant and recessive: Mendel showed a hidden trait can resurface intact a generation later, overturning the common belief that parents' features simply blend in their young.

What name is given to the alternative versions of one gene?

Alleles are inherited in pairs, one from each parent, which is how a person ends up with type AB blood: one allele for A and one for B.

On which ship did Charles Darwin make his five-year voyage?

Darwin sailed on HMS Beagle for nearly five years under Captain Robert FitzRoy, aboard as a gentleman naturalist rather than a paid crew member.

Which phrase did Darwin borrow from Herbert Spencer?

Survival of the fittest was coined by Spencer in 1864, after he had read Darwin's book; Darwin then took it up in the fifth edition of On the Origin of Species, meaning best adapted to the local environment.

Which naturalist sent Darwin an essay in 1858 describing the same idea of natural selection?

Alfred Russel Wallace, writing from the Malay Archipelago, sent Darwin his essay in 1858; the two men's papers were read together at the Linnean Society of London that July.

Where is Charles Darwin buried?

Darwin lies in Westminster Abbey a few feet from Isaac Newton, an honour arranged after the president of the Royal Society telegraphed the Dean to ask for it.

In a food chain, what is another name for an autotroph such as grass or algae?

Producers such as grass and algae make their own food from sunlight, so every animal further up the chain, grazer or hunter, is running on energy they captured first.

What term describes a poison such as DDT growing more concentrated at each step up a food chain?

Biomagnification left DDT most concentrated in birds of prey at the top of the chain, thinning the eggshells of eagles and falcons until the US banned the pesticide in 1972.

What term describes the non-living components of an ecosystem, such as soil?

Abiotic factors such as soil, water, temperature and sunlight are not alive, yet they supply the energy and nutrients living things depend on, so they shape what can live where.

Which organisms release carbon back to the atmosphere by breaking down dead matter?

Decomposers such as fungi and bacteria digest dead matter and release its carbon as carbon dioxide; without them, dead leaves and animals would simply pile up.

Who published the first generally accepted periodic table, in 1869?

Dmitri Mendeleev published his table in 1869, leaving gaps for undiscovered elements and predicting the properties of gallium and germanium before they were found.

How many chemical elements had been officially confirmed as of 2025?

118 elements fill the table's first seven rows exactly: the last four gaps were confirmed in December 2015 and named nihonium, moscovium, tennessine and oganesson in 2016.

Which element has atomic number 1?

Hydrogen is the lightest element, so it once lifted airships; the Hindenburg, filled with it, was destroyed by fire in 1937.

The rightmost column of the periodic table, group 18, holds which family of elements?

Group 18 is the noble gases, helium through radon, whose full outer electron shells make them almost unreactive; group 1 on the far left is the alkali metals.

In chemistry's table of the elements, what are the horizontal rows called?

Rows are periods, each one filling a new electron shell, while columns are groups whose elements tend to behave alike.

Newton's first law expresses which principle?

Inertia means a moving body keeps going unless a force stops it, the reverse of the view that prevailed for nearly 2,000 years, that motion needs a continual push; Galileo deduced it from balls rolling down ramps.

Which astronomer paid to publish Newton's Principia?

Edmond Halley covered the printing costs because the Royal Society had spent its book budget on a lavish history of fishes; it later paid his salary in unsold copies of that book.

In Newton's third law, when two bodies push on each other, the forces are what?

Equal and opposite: the two forces match in size but point opposite ways, which is why a rocket moves forward as its exhaust is pushed backward.

Newton's second law says net force equals mass multiplied by what?

Acceleration: F = ma means the same push speeds up a light object more than a heavy one, which is why an empty trolley is easier to get moving than a full one.

Who proposed the theory of continental drift in 1912?

Alfred Wegener, a German meteorologist, proposed continental drift in 1912, arguing from matching coastlines and fossils that the continents had once been joined in a supercontinent, Pangaea.

What is the process called when one tectonic plate is carried down under another?

Subduction carries one plate down beneath another into the mantle; deep ocean trenches such as the Mariana Trench mark where it happens.

Which plate's 'Ring of Fire' holds most of the world's active volcanoes?

Pacific Plate edges trace much of the Ring of Fire, where ocean floor sinks beneath neighbouring plates and the magma this generates feeds most of the world's volcanoes.

Which technology lets geologists measure tectonic plates creeping a few centimetres a year?

GPS receivers fixed to the ground can track movement to within a fraction of a millimetre a year; they show plates drifting about as fast as fingernails grow.

At which type of plate boundary do plates grind sideways past each other, as along California's San Andreas Fault?

Transform boundaries neither create nor destroy crust; the San Andreas is one of the few on land, as most lie hidden on the ocean floor.

What is an underground layer of rock that holds groundwater called?

Aquifers refill as rain seeps down through the soil, so pumping water out faster than it is replaced runs them down.

What is the name for water vapour released from plants into the atmosphere?

Transpiration is water vapour escaping through leaf pores called stomata; the plant has to open them to take in carbon dioxide, so losing water is the price of feeding itself.

In which Italian city is Romeo and Juliet set?

Verona is where the play opens, with a street brawl between servants of the feuding Montagues and Capulets; Romeo is later banished from the city to Mantua.

At the start of Romeo and Juliet, which girl is Romeo pining for?

Romeo is pining for Rosaline, a niece of Capulet who has sworn off love; he only goes to the Capulet ball hoping to see her there.

Who secretly marries Romeo and Juliet, hoping to reconcile their families?

Friar Laurence marries them in secret hoping to end the feud, and later gives Juliet the sleeping potion that sets up the tragic ending.

Which hot-headed cousin of Juliet challenges Romeo to a duel?

Tybalt, Juliet's cousin, challenges Romeo after the ball; Romeo, now secretly his kinsman by marriage, refuses, and Tybalt kills Mercutio instead.

Whom does Capulet want Juliet to marry?

Capulet wants Juliet to marry Count Paris, a kinsman of the Prince; he first asks Paris to wait two years, then invites him to the ball.

Which musical moved Romeo and Juliet to 1950s New York?

West Side Story (1957) swaps the feuding Montagues and Capulets for two rival street gangs, the Jets and the Sharks.

Who narrates To Kill a Mockingbird?

Scout Finch, Jean Louise, tells the story as an adult looking back, so the book pairs a six-year-old's view of events with a grown woman's hindsight.

In which Alabama town is To Kill a Mockingbird set?

Maycomb is invented, but Harper Lee modelled it on her hometown of Monroeville, where a local cast now stages the story as a play at the old courthouse every May.

Whom does Atticus Finch defend at trial in To Kill a Mockingbird?

Tom Robinson, a Black man, is falsely accused of raping a white woman, Mayella Ewell; Atticus shows her own father is the likelier attacker, yet the jury convicts Tom anyway.

Which award did To Kill a Mockingbird win the year after it was published?

Pulitzer Prize for Fiction, 1961: the winning book was a rewrite, after Harper Lee's editor persuaded her to rebuild an earlier draft around its childhood flashbacks.

What is Dill's real name in To Kill a Mockingbird?

Charles Baker Harris arrives each summer to stay with his aunt; Lee modelled him on her own childhood friend and next-door neighbour, the future writer Truman Capote.

Who wrote Of Mice and Men?

John Steinbeck published Of Mice and Men in 1937, drawing on his teenage summers working beside migrant farm workers in California's Salinas Valley.

In Of Mice and Men, which animals does Lennie dream of tending on the farm?

Lennie dreams of tending the rabbits on the farm he and George plan to buy; he loves petting soft things, which is exactly what gets him into trouble.

The title Of Mice and Men comes from a poem by which writer?

Robert Burns's 'To a Mouse', said to follow his ploughing up a mouse's nest, warns that the best-laid schemes of mice and men 'gang aft agley': often go wrong.

In Of Mice and Men, which ageing ranch hand offers his savings to buy into George and Lennie's farm?

Candy, the one-handed old swamper, offers his savings soon after Carlson shoots his ageing dog, and for a moment the farm looks within the men's reach.

Which stable hand in Of Mice and Men is isolated from the others because he is black?

Crooks, the crippled Black stable buck, lives apart in the harness room; he scorns the farm dream yet asks whether he could hoe a garden patch there.

Odysseus is king of which island?

Odysseus rules Ithaca, yet after ten years at war and ten more getting home he has to slip back into his own palace disguised as a beggar before he can reclaim it.

Which other ancient epic, like the Odyssey, has 24 books?

The Iliad matches the Odyssey's 24 books; Virgil later modelled his Aeneid on the pair in half the space, with six books of wandering like the Odyssey and six of war like the Iliad.

How does Penelope put off the suitors in the Odyssey?

She unweaves a shroud each night: Penelope vows to pick a suitor once the shroud for her father-in-law Laertes is finished, and the trick holds for three years until a maid gives her away.

Which nymph keeps Odysseus on her island for seven years, offering him immortality if he stays?

Calypso holds Odysseus on Ogygia until the gods order her to let him go; he turns down her offer of eternal youth and sets off on a raft, still set on getting home to his wife.

Which of Odysseus's weapons do Penelope's suitors fail to master?

Bow: not one suitor can even string it, but the disguised Odysseus strings it with ease, shoots an arrow through a row of twelve axes and then turns the weapon on the suitors.

What does Ralph use to summon the other boys to meetings in Lord of the Flies?

A conch shell first calls the boys together when Ralph blows it, and whoever holds it may speak; when a boulder finally smashes it, the island's last trace of order goes with it.

Whose glasses do the boys use to start the signal fire in Lord of the Flies?

Piggy's glasses focus the sun to light the fire; later Jack's hunters raid the camp at night to steal them, and the power to make fire changes hands with them.

Which Victorian novel about three shipwrecked boys did William Golding answer darkly with Lord of the Flies?

Golding took R. M. Ballantyne's The Coral Island, thought its cheerful castaways unrealistic, and set out to write the opposite; Ralph and Jack even share names with Ballantyne's heroes.

What was William Golding's job when he wrote Lord of the Flies?

Schoolteacher: Golding taught at Bishop Wordsworth's School in Salisbury, left to serve in the Royal Navy, commanding a rocket-launching craft on D-Day, then returned to the classroom and wrote the novel.

Which two pigs take command after Old Major dies in Animal Farm?

Snowball and Napoleon lead together at first, but while one runs reading classes the other quietly rears nine puppies into the guard dogs that later chase his rival off the farm.

Which of Animal Farm's Seven Commandments ends up alone on the barn wall?

'All animals are equal' is the seventh commandment; by the end it alone remains on the barn wall, amended to 'but some animals are more equal than others'.

What ambitious building project is proposed to modernise the farm in Animal Farm?

A windmill to generate electricity is the plan; when the half-built tower collapses in a storm, the pigs blame sabotage by an exiled rival, though the humans say its walls were too thin.

Which real events did Orwell say Animal Farm reflects?

The Russian Revolution and Stalin's betrayal of it are the fable's targets; several publishers turned the book down in 1944, while the Soviet Union was still a prized wartime ally.

Which pig in Animal Farm serves as the ruling pigs' smooth-talking orator and propagandist?

Squealer, said to be able to turn black into white, explains away every broken rule, and is once found stunned beside a broken ladder under the commandments he has been altering by night.

Who narrates The Great Gatsby?

Nick Carraway narrates as Gatsby's neighbour and Daisy's cousin, which is why Gatsby asks him to invite her to tea and so stage the reunion he has waited five years for.

In The Great Gatsby, in which Long Island village does Gatsby's mansion stand?

West Egg is 'the less fashionable of the two' in the narrator's words, home to new money like Gatsby; Daisy and Tom live across the bay in old-money East Egg.

What colour is the light Gatsby stares at across the bay?

Green is the light at the end of Daisy's dock; Gatsby is first glimpsed stretching his arms toward it across the dark water, and it comes to stand for his longing to win her back.

What is Jordan Baker's sport in The Great Gatsby?

Jordan Baker is a golf champion and a childhood friend of Daisy's from Louisville, rumoured to have moved her ball in a tournament.

Which figure of speech makes an implied comparison, without using 'like' or 'as'?

A metaphor states one thing is another: 'All the world's a stage' is the textbook example, where a simile would say the world is like a stage.

Mesopotamia lay between which two rivers?

Tigris and Euphrates: Mesopotamia is Greek for the land 'between rivers', and canals dug from the two turned a dry plain into farmland that fed some of the world's earliest civilisations.

Which lawgiving king made one city the leading power of Mesopotamia in the 18th century BC?

Hammurabi, sixth king of his dynasty, conquered Larsa, Eshnunna and Mari to bring almost all of Mesopotamia under one rule; his law code survives carved on a tall stone stele.

By tradition, which king first united Upper and Lower Egypt and founded the First Dynasty?

Menes is the unifier named by ancient tradition; he is often identified with Narmer, whose carved palette shows a king wearing the crowns of both Upper and Lower Egypt.

During which period were the Giza pyramids and the Great Sphinx built?

The Old Kingdom's Fourth Dynasty raised the three great Giza pyramids as royal tombs for a father, his son and his grandson, around 2600–2500 BC, long before the New Kingdom.

Which discovery let scholars finally decipher hieroglyphs in the 1820s?

The Rosetta Stone, found in 1799, carries the same decree in hieroglyphs, Demotic and Greek; Thomas Young and then Jean-François Champollion, in 1822, used it to crack the script.

Which pharaoh fought the Hittites at Kadesh and later made peace with them by treaty?

Ramesses II had Kadesh carved on his temple walls as a great victory, though the battle was closer to a draw; years later he sealed one of the earliest surviving peace treaties with the Hittites.

At which 480 BC pass did three hundred Spartans hold off the Persians for days?

At Thermopylae in 480 BC, Leonidas and his 300 Spartans, with several thousand other Greeks, held the narrow pass against Xerxes' army for three days before being outflanked.

The Peloponnesian War was fought between Athens and which rival city-state?

Sparta led the Peloponnesian League against Athens from 431 to 404 BC; a plague early in the war killed the Athenian statesman Pericles.

The ancient Olympic Games were held at Olympia every four years in honour of which god?

Zeus was honoured at Olympia, where the Games are traditionally dated from 776 BC; a sacred truce was proclaimed so that athletes and pilgrims could travel to them in safety.

Which philosopher tutored the young Alexander the Great?

Aristotle tutored Alexander at Mieza from about 343 BC; Plutarch says Alexander kept a copy of the Iliad annotated by Aristotle under his pillow on campaign.

Which Persian king did Alexander overthrow?

Darius III lost to Alexander at Issus in 333 BC and Gaugamela in 331 BC, then fled east and was murdered by his own satrap Bessus in 330 BC.

Which river did Julius Caesar cross with his army in 49 BC, defying the Senate?

Caesar crossed the Rubicon, the boundary between Cisalpine Gaul and Italy, in January 49 BC, starting a civil war; 'crossing the Rubicon' became a phrase for passing a point of no return.

Which senator, pardoned and promoted by Julius Caesar, helped lead his assassination on the Ides of March?

Brutus and Cassius led the senators who stabbed Caesar at a Senate meeting on 15 March 44 BC; meant to save the Republic, the killing instead set off the civil wars that finished it.

With Crassus and Pompey, Caesar formed which informal alliance in 60 BC?

The First Triumvirate, an informal pact of 60 BC, dominated Roman politics until Crassus died at Carrhae in 53 BC and Caesar and Pompey fell out.

Which title did the Senate grant Octavian in 27 BC, making him the first emperor?

Augustus, 'the revered one', was a brand-new honorific; in theory he had restored the Republic and was merely its princeps, or first citizen, while keeping the real power himself.

Under which emperor did Rome reach its greatest territorial extent?

Under Trajan the empire reached its greatest extent in AD 117, after his conquests of Dacia and Mesopotamia; his successor Hadrian gave up the eastern gains.

Which emperor made Byzantium his new imperial capital in 330, a 'New Rome' in the east?

Constantine dedicated the rebuilt city on 11 May 330, and it soon took his own name, Constantinople; he had already legalised Christianity with the Edict of Milan in 313.

What name is given to the two centuries of stability that began under Rome's first emperor?

Pax Romana means 'Roman peace': from 27 BC to AD 180 the empire enjoyed two centuries of relative calm, though its armies kept fighting frontier wars and putting down revolts.

Which English king sealed Magna Carta at Runnymede in 1215?

King John sealed Magna Carta at Runnymede on 15 June 1215; Pope Innocent III annulled it within months, sparking the First Barons' War.

Who holds two of the four surviving 1215 Magna Cartas?

The British Library holds two of the four 1215 originals; the others belong to the cathedrals of Lincoln and Salisbury, which were sent their copies when the charter was issued.

Which bacterium caused the Black Death?

Yersinia pestis is named after Alexandre Yersin, who identified it during a plague outbreak in Hong Kong in 1894; it reaches people mainly through the bites of infected fleas.

Fleas carried by which animals have long been blamed for spreading the Black Death across Europe?

Rats long took the blame, but a 2018 study found the spread fits human fleas and body lice better than rat fleas; either way the plague killed up to half of Europe's people.

Caffa, the Crimean port where plague reportedly reached Europeans in 1347, was a colony of which Italian city?

Genoa ran Caffa as a Black Sea trading post; a besieging Mongol army reportedly hurled plague corpses over its walls, and Genoese ships leaving the port carried the disease on to Sicily.

In which Italian city did the Renaissance begin?

The Renaissance began in Florence in the 14th century, where the wealth of its bankers and the Medici family's patronage funded artists and scholars.

Which Renaissance sculptor reluctantly spent four years painting a chapel ceiling for Pope Julius II?

Michelangelo saw himself as a sculptor, not a painter, and tried to pass the job to Raphael, yet between 1508 and 1512 he covered the Sistine Chapel ceiling with scenes from Genesis.

Which architect built the great cathedral dome after losing the 1401 Baptistery doors contest?

Filippo Brunelleschi lost the 1401 Baptistery doors contest to Ghiberti, then engineered the dome of Florence Cathedral (1420–1436), raised without a wooden centering frame.

Which Renaissance political thinker set out to describe how rulers really behave, not how they should?

Machiavelli wrote The Prince around 1513 as blunt advice on winning and keeping power; its reputation turned his name into 'Machiavellian', a byword for cunning and ruthless statecraft.

What was stormed in Paris on 14 July 1789?

The Bastille, a royal fortress and prison in eastern Paris, was stormed by a crowd seeking its store of gunpowder; 14 July later became France's national day.

Which national anthem was written in Strasbourg in 1792 as a war song for the Army of the Rhine?

La Marseillaise was written overnight by an army captain, Rouget de Lisle; it got its name when volunteer troops from Marseille sang it on their march to the capital.

What did France's Third Estate deputies swear in June 1789 after finding their meeting hall locked?

The Tennis Court Oath of 20 June 1789: locked out of their hall at Versailles, the deputies met in a royal tennis court and vowed not to disperse until France had a constitution.

Who led the radical Jacobins on the Committee of Public Safety during the Terror?

Maximilien Robespierre dominated the Committee of Public Safety from July 1793 until he was guillotined himself on 28 July 1794; about 16,600 people were formally sentenced to death during the Terror.

Which French king was guillotined months after the monarchy was abolished?

Louis XVI was tried by the National Convention as plain 'Citizen Louis Capet' and convicted of treason; his failed flight to Varennes in 1791 had already hardened Parisian hostility to the crown.

In which country did the Industrial Revolution begin around 1760?

The Industrial Revolution began in Great Britain around 1760, driven by coal, canals and steam power, and had spread to continental Europe and the US by about 1840.

Who invented the spinning jenny in 1764?

James Hargreaves, a Lancashire weaver, built the spinning jenny around 1764, letting one worker spin eight threads at once; Arkwright's water frame followed five years later.

Which American inventor patented the cotton gin in 1794?

Eli Whitney's gin made cotton so profitable that it entrenched Southern slavery, yet rivals copied the simple machine so freely that he lost much of his own profit to patent lawsuits.

Which industry was the first to use modern production methods in the Industrial Revolution?

Textiles led the way: spinning and weaving machines moved cotton work out of cottages and into water- and steam-powered mills, and cloth became the era's dominant industry by jobs and output.

Whose assassination in Sarajevo on 28 June 1914 triggered World War I?

Archduke Franz Ferdinand survived a bomb thrown at his motorcade that morning; Gavrilo Princip got his chance only when the archduke's driver took a wrong turn and stopped right in front of him.

What made the United States join the Allies in April 1917?

Germany resumed unrestricted submarine warfare on 1 February 1917, gambling it could starve Britain before American troops arrived; that, plus the Zimmermann Telegram, brought the US declaration of war on 6 April.

On what date did the armistice ending World War I take effect?

11 November 1918 at 11 a.m. is when the guns fell silent, about six hours after the signing in Marshal Foch's railway carriage at Compiègne; fighting went on right up to the deadline.

Which 1919 settlement made Germany lose territory, disarm and pay reparations?

The Treaty of Versailles cut Germany's army to 100,000 men and, in its 'war guilt' clause, made Germany accept the blame for the war; bitterness over those terms shaped German politics for decades.

Which gas did Germany first use at the Second Battle of Ypres in April 1915?

Germany released chlorine from thousands of cylinders at Ypres on 22 April 1915 and let the wind carry the cloud over French lines, the first large-scale use of lethal gas in the war.

Which failed Allied campaign followed the Ottoman Empire joining the Central Powers?

The Gallipoli campaign of 1915–16 tried to force the Dardanelles and knock the Ottomans out of the war after they joined the Central Powers in late 1914; the Allies evacuated in January 1916.

Which 1962 standoff is considered the closest the Cold War came to nuclear war?

The Cuban Missile Crisis of October 1962 began when US spy planes found Soviet missile sites in Cuba; Khrushchev withdrew them for a US no-invasion pledge and the quiet removal of Jupiter missiles from Turkey.

Which Soviet-led alliance was formed in 1955 to match NATO?

The Warsaw Pact was signed in May 1955 by the USSR and seven Eastern Bloc states, days after West Germany joined NATO, which had been founded in 1949.

In Ray Bradbury's Fahrenheit 451, what is Guy Montag's job?

Book-burning fireman Guy Montag starts fires instead of fighting them in Bradbury's 1953 novel; sickened by the work, he flees and joins exiles who each memorise a book to keep it alive.

Elie Wiesel's memoir Night recounts his time with his father in Auschwitz and which other camp?

Buchenwald is where Wiesel's father died in January 1945, less than three months before American troops reached the camp; Elie, then sixteen, was among those liberated.

An element's atomic number equals the number of what in each of its atoms?

Protons define the element: every atom of an element carries the same number of them, while the neutron count can vary, which is what makes different isotopes of that same element.

What attraction holds sodium chloride, table salt, together as a solid?

Oppositely charged ions, Na⁺ and Cl⁻, each pull on six neighbours of the other kind in a rigid lattice, which is why salt forms hard little cubes that melt only at about 800 °C.

Roughly what is Avogadro's number, the number of particles in one mole?

6.022 × 10²³ carries Avogadro's name, but he never knew its value: Jean Perrin, who estimated it from his own experiments, coined the term in 1909, half a century after Avogadro died.

Which formula gives the circumference of a circle with radius r?

Circumference is 2πr; since the diameter is twice the radius, that equals π times the diameter, while πr² gives the area.

Who is the teenage narrator of J. D. Salinger's The Catcher in the Rye?

Holden Caulfield tells his story from what seems to be a California sanatorium, looking back on the days after his expulsion from Pencey Prep, when he drifted around New York rather than go home to his parents.

Which flagship of Columbus's first voyage ran aground and was lost at Christmas 1492?

The Santa María ran aground off Hispaniola on Christmas Day 1492; her timbers went into a fort named La Navidad, and Columbus sailed home to Spain aboard the little Niña instead.

The hertz, the SI unit of frequency, equals one cycle per what?

Second: one hertz is one cycle per second, and the unit honours Heinrich Hertz, who proved in the 1880s that the electromagnetic waves Maxwell had predicted really exist.

Density is defined as the ratio of a substance's mass to its what?

Density is mass divided by volume, which is why a kilogram of feathers takes up far more space than a kilogram of lead.

Osmosis is the net movement of solvent molecules through what kind of membrane?

Osmosis happens across a selectively permeable membrane that lets water through but not dissolved solutes; water moves from lower to higher solute concentration until the two sides even out.

In Great Expectations, which escaped convict accosts young Pip in a graveyard?

Abel Magwitch, an escaped convict from the prison hulks, seizes Pip among the graves on the Kent marshes and later becomes his secret benefactor.