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Matter

32 articles

Acids and bases

Lemon juice tastes sour and soap feels slippery. Acids and bases differ in the ions water carries, and pH counts them in powers of ten.

Alkali and alkaline earth metals

Sodium fizzes in water and caesium explodes. Compare the two most reactive families of metals, row by row, and see why.

Alloys

Pure gold bends in your fingers, yet 18-carat gold, a quarter copper and silver, keeps its shape for decades. Why does a mix of metals beat either one?

Atoms

Everything is built from atoms, and one number decides which kind. Add protons one at a time and watch hydrogen become carbon, oxygen, and neon.

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Brownian motion and random walks

A speck in still water jiggles forever with nothing alive to drive it. Unseen molecules explain why, and why its spread grows only as √time.

Carbon allotropes

Diamond and pencil lead are both pure carbon. Rearrange the same atoms and you get the hardest natural material, a slippery solid or a molecular football.

Catalysts

A car's exhaust is cleanest once the engine is warm. A catalyst offers a reaction an easier path with a lower barrier, and is never used up.

Chemical bonding

Salt shatters, copper bends and diamond scratches glass. Slide one layer of atoms over the next and see how the way atoms hold on decides which.

Chemical equilibrium

A sealed flask of brown gas pales in ice and darkens in hot water. A reaction that runs both ways settles where its two rates match.

Chemical reactions

Milk sours faster on a warm day. Molecules react only when they collide hard enough and the right way round, and warmth makes that happen more often.

Combustion

A flame needs fuel, oxygen and heat. Take any one away and it dies. Why those three, and how can a little water put out a fire?

Compounds

Hydrogen burns and oxygen feeds fire, yet together they make water. Why does a compound always hold its elements in exactly the same ratio?

Conductors, insulators and semiconductors

Copper carries current, diamond does not, and silicon sits in between. Widen the gap between energy bands and heat the crystal to see why.

Crystals

Salt grains are tiny cubes and snowflakes have six arms. Zoom to the atoms a crystal for its repeating pattern, and see why slow cooling grows big ones.

Electrochemistry

Dip two different metals in salt solutions, join them with a wire, and a current flows. Where does that voltage come from, and why does it sag?

Gas laws and kinetic theory

Squeeze a gas and its pressure rises; heat it and it rises again. Tiny particles in a box show why, and why their speeds follow one curve.

Halogens and noble gases

Chlorine attacks almost anything; argon, one proton heavier, reacts with nothing. Bring sodium near each and see what one gap in a shell does.

Hydrogen, oxygen, nitrogen

A burning splint flares in oxygen, dies in nitrogen and pops at hydrogen. Test all three, then look inside at the bonds that make the difference.

Isotopes

Every carbon atom has six protons, but not every one has six neutrons. Add neutrons to a nucleus and find out why only a few mixes last.

Metalloids

Silicon shines like a metal, shatters like glass and conducts better as it warms. Heat six in-between elements and look inside their crystals.

Mixtures and solutions

Stir salt into water and it disappears, yet it is still there. Find out where it went, why hot water takes more, and what happens when the water is full.

Molecules

Atoms rarely travel alone. They join in small fixed groups whose shape decides how they behave. Pick a molecule, heat it, and see it as a chemist does.

Natural materials

Wood, bone, shell and silk are built from a few weak ingredients, yet rival steel per kilogram. Bend them to breaking and zoom inside.

Non-metals

Most non-metals are gases, one is a liquid and a few are solids. Warm a cabinet of them and see how their molecules decide which.

Organic chemistry and hydrocarbons

Methane is a gas, petrol a liquid and candle wax a solid, yet all are carbon chains. Grow one, swap its end, and watch the boiling point move.

Polymers and plastics

A carrier bag stretches and stays stretched; a rubber band springs back; a plug socket cracks. All three are long chains. Pull them and see why.

Radioactive decay

No one can say when a single unstable nucleus will decay, yet a large sample halves on a clockwork schedule. Watch randomness turn into a rule.

States of matter

An ice cube. A drop of water. Invisible vapor. Explore how the same molecules make three very different worlds.

Superconductivity

Cool some materials far enough and their electrical resistance vanishes. Then they push a magnet's field away, and the magnet floats.

Surface tension and capillarity

Water climbs up a thin glass tube on its own, and climbs higher the thinner the tube. Change the tubes and the liquid, and see why.

The periodic table

The elements fall into rows of 2, 8, 18 and 32. Add them one proton at a time and watch the table build its own lopsided shape.

Transition metals

Copper sulfate dissolves blue, nickel salts green, zinc salts clear. Why do transition-metal ions colour water, and why do a few not?

Energy and forces

46 articles

Angular momentum and gyroscopes

A skater pulls in her arms and spins faster. A spinning top circles instead of falling. Both follow one rule about things that turn.

Atomic spectra

Pass a spark through hydrogen and a prism splits its glow into four thin lines, not a rainbow. Why does every element shine with its own barcode?

Blackbody radiation

Heat a lump of metal and it glows dull red, then orange, then white. Why does a hotter thing shine in a different colour, not just more brightly?

Capacitors

Two metal plates and a gap store charge and energy from a battery. Why does a narrower gap, or a sheet of glass, let them hold more?

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Charged particles in magnetic fields

A magnet cannot speed an ion up or slow it down, yet it can bend its path into a perfect circle. How does that circle weigh atoms?

Circuits in series and parallel

Three bulbs in a row glow dimly, but side by side they blaze. Follow the current as it splits and the voltage as it falls round every loop.

Circular motion

Whirl a ball on a string and it goes round; let go and it flies off. Find what keeps it turning, and which way it really escapes.

Diffraction

You can hear someone around a corner but not see them. Send straight waves through a gap and watch how its width decides whether they spread.

Doppler effect

An ambulance siren drops in pitch the moment it passes you. Move a source through its own waves and see the crests bunch up ahead and stretch out behind.

Electric fields and potential

Charges push and pull across empty space. Field lines show which way, and a landscape of voltage shows why a charge rolls the way it does.

Electricity

A battery, a wire and a bulb. Push harder or get in the way, and watch what the current does. Then open the wire and see what it is made of.

Electromagnetic induction

Move a magnet near a coil of wire and a current flows. Push it, spin it, add turns, and see how motion becomes electricity in every generator.

Electromagnetic spectrum

Radio, microwaves, light, X-rays: one kind of wave at different lengths. Slide across fifteen powers of ten and see what changes, and what does not.

Electromagnets

A coil of wire becomes a magnet the moment current flows, and stops when it does. Change the current, the turns and the core, and watch what it lifts.

Entropy and heat engines

A flame can turn a wheel, but never with all of its heat. Why must every engine give some heat away, and how much can become work?

Floating and buoyancy

A steel ship floats while a steel nail sinks. Change what a cube is made of and what it sits in, and see what decides.

Fluid flow and Bernoulli

Narrow a pipe and the water inside speeds up. Glass columns on top show its pressure falling exactly where it runs fastest. Why?

Friction

A box on a ramp stays put until, at one particular angle, it suddenly slides. Tilt a board and change its surface to find that angle.

Gravity

Every mass pulls on every other. Change how heavy two bodies are and how far apart they sit, and watch the pull set their dance.

Heat and temperature

Heat one end of a bar and watch warmth creep along it, particle by particle. Then swap the metal for wood and see why it stops.

Interference

Two sets of ripples cross without bumping into each other, yet together they draw lines of perfectly still water. Where do the calm lines come from?

Kinetic and potential energy

A roller coaster has no engine after the first hill, yet it races round a loop. Change where the car starts and watch its energy change form.

Laws of motion

A shopping trolley is easy to start empty and hard to start full. Push a fan cart along a track to see the three rules that govern every push and pull.

Lenses

A magnifying glass can enlarge a page or throw a tiny upside-down picture of a window onto a wall. Slide a lit arrow along a bench to see why.

Magnetism

A magnet reaches out through empty space. Bring two together and see the invisible field that pulls them close or pushes them apart.

Momentum and collisions

A rolling cart hits a parked one. Some crashes stick and some bounce. Change the masses and the bounce, and find what no crash can change.

Motion graphs

A cart rolls, slows, stops and comes back. Three graphs of that one trip tell you where it was, how fast it went and how its speed changed.

Nuclear fission

One neutron splits a uranium nucleus, which frees two or three more. Whether that chain fizzles, holds steady or runs away comes down to a single number.

Nuclear fusion

The Sun shines by fusing light nuclei at 15 million kelvin. To fuse on Earth we need ten times hotter. Heat a plasma and see why.

Particle physics and the Standard Model

A proton is three quarks, yet they make up only about 1% of its mass. Open one up, try to pull a quark out, then see every known particle on one chart.

Pendulums

A weight on a string keeps steady time. Change the length, the gravity and the swing, and find out what really sets the beat.

Photoelectric effect

Light knocks electrons out of a metal, but only above a threshold frequency. Why does the colour of the light decide this, not its brightness?

Polarisation

Turn one polarising filter over another and the view through them fades to black. Why, and how can adding a third filter bring the light back?

Pressure

A gas pushes on everything around it, and the push is made of nothing but tiny collisions. Squeeze the cylinder and heat the gas to feel why.

Prisms and rainbows

Sunlight looks white, yet a prism or a raindrop fans it into colours. Trace a beam through glass and water to find out why a rainbow sits at 42°.

Projectile motion

A thrown ball follows a curve you can predict. Change the angle, the speed and the air, and find which launch flies farthest.

Quantum tunnelling

A ball can't roll through a hill too high to climb, but an electron can pass through a thin wall. The thicker the wall, the less of it gets through.

Refraction

A straw looks snapped where it enters water. Tilt a beam into glass and out again to see why light bends, and when it cannot escape at all.

Resonance

Small pushes at just the right rhythm can build a huge swing. Push a pendulum fast, slow and in step, and see why timing beats strength.

Sound

Sound is a squeeze that travels. Push the air at one end, and a pattern of crowding and spreading runs down the tube while the air itself stays put.

Special relativity

Light always moves at the same speed, whoever measures it. Follow that rule onto a fast train and moving clocks must run slow.

Springs and simple harmonic motion

A weight on a spring bounces in perfect time, big bounce or small. Change the spring and the mass, and see what sets the beat.

Standing waves and music

A string or pipe rings only at notes whose waves fit its length. See the ladder of harmonics, and why a guitar and a flute sound different.

Static electricity

Rub a balloon on your hair and it lifts scraps of paper that carry no charge at all. How can a charge pull on something neutral?

Wave–particle duality

Fire electrons at two slits one at a time. Each lands as a single dot, yet thousands draw stripes only waves can make. What is an electron?

Waves

Tap still water and rings spread out, yet the water stays put. What travels, and what sets how far apart the crests are?

Space

18 articles

Black holes

Squeeze enough mass into a small enough space and not even light gets out. See how a black hole bends light into a dark shadow ringed with fire.

Comets and asteroids

Comets and asteroids are both leftovers from the birth of the planets, yet only a comet grows a glowing head and two tails near the Sun. Why?

Dark matter and rotation curves

Stars at a galaxy's edge orbit as fast as those near its middle. Weigh the galaxy by its spin, and most of its mass turns out to be invisible.

Earth and Moon

The Moon changes shape every night, drags the oceans about, and now and then blots out the Sun. One orbit under one light explains all three.

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Exoplanets

Most planets beyond the Sun are found without being seen. When one crosses its star, the starlight dips slightly, and that dip is the clue.

Galaxies

The Milky Way is one of hundreds of billions of galaxies. Their shapes tell their histories, and their spin points to matter no one can see.

Gravitational lensing

A heavy galaxy bends the light of a galaxy far behind it. Line them up, and the one behind is stretched into arcs, four images or a ring.

Gravitational waves

Two black holes circling each other shake space itself. Watch the ripples spread, then see them stretch a detector on Earth by less than a proton's width.

Lagrange points

A probe can keep pace with Earth round the Sun at five special places. Find the balance points, and why space telescopes park at L2.

Nebulae

Some clouds in space glow pink, some shine blue and some are black shapes against the stars. What decides which one a cloud becomes?

Neutron stars and pulsars

A dead star's core, the size of a city, spins up to hundreds of times a second. Why does it reach us as a steady tick of radio pulses?

Orbits and Kepler's laws

Planets do not go round in circles, and they do not keep a steady speed. Stretch an orbit and find the rule that keeps time anyway.

Star life cycle

Stars are born, burn for millions or trillions of years, and die in ways set on the day they form. Pick a starting mass and scrub through a whole life.

The cosmic distance ladder

No tape measure reaches a star. Astronomers reach the far galaxies on a ladder of methods, each rung calibrated by the one below it.

The cosmic microwave background

A faint microwave glow fills the whole sky. It is light from the Big Bang's fiery fog, freed 380,000 years in and stretched ever since.

The expanding universe

Almost every galaxy is moving away from us, faster the farther it is. That does not put us at the centre. Space itself is stretching.

The Solar System

One star, eight planets, and a lot of empty space. Run the clock and see why the inner planets race while the outer ones crawl.

The Sun

Every eleven years the Sun's face breaks out in dark spots, then clears again. Cut the Sun open and follow the magnetic field that makes them.

Earth

21 articles

Auroras

Curtains of green and red light ripple over the poles when the solar wind shakes Earth's magnetic field. Turn up a solar storm and watch them spread.

Climate

Sunlight comes in, heat goes out, and a few gases in the air decide how much gets away. Change their amount and watch the ground warm.

Earth's magnetic field

A compass points north because liquid iron churns 3,000 km down. Run time back to watch the field flip, and the sea floor record each flip.

Earthquakes and seismic waves

No drill has gone deeper than about 12 km, yet we know the Earth's core is liquid. Earthquake waves crossing the planet gave it away.

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El Niño

Every few years the warm water of the Pacific slides east and the rain follows it, from Indonesia to Peru. Weaken the trade winds and watch it go.

Erosion and weathering

Rain and rivers wear whole mountains away, grain by grain. Run two million years of rain over an upland and see where its rock goes.

Glaciers and ice sheets

Snow that outlasts the summer piles up into ice that flows like a slow river. How does an ice sheet grow, move, bend the ground and drain the sea?

Groundwater and aquifers

Dig deep enough almost anywhere and the hole fills with water. Where does it come from, and what happens to it when a well starts pumping?

Ice ages and Milankovitch cycles

Ice sheets have grown and melted for 400,000 years in step with slow wobbles in Earth's orbit. How can such small changes start an ice age?

Layers of the atmosphere

Climb a mountain and the air gets colder. Keep climbing and it warms again, cools, then turns hot. Rise through the air and see why.

Ocean currents

The Gulf Stream is pushed by the wind. The deep ocean moves for another reason, cold, salty water sinking near the poles. Change the water and see.

Plate tectonics

The ground under your feet is drifting a few centimetres a year. Over millions of years that opens oceans, raises mountains and shakes cities.

Radiometric dating and the age of the Earth

A zircon crystal smaller than a grain of sand has kept time since it grew. Count its uranium and its lead, and read off its age, and the Earth's.

Rocks and the rock cycle

Granite crumbles to sand, sand hardens into sandstone, and sandstone buried deep turns to gneiss and melts. Follow one rock all the way round.

Seasons

Earth is closest to the Sun in January, yet that is midwinter in the north. A tilted axis, not distance, makes summer and winter.

Storms and weather

One summer afternoon ends with a few white puffs, another in a thunderstorm. Heat the ground, add moisture and wind, and see which one grows.

The Coriolis effect

Throw a ball across a turning carousel and its path curves. On a spinning planet the same turn bends the winds and sets storms spinning.

The ozone layer

A gas spread so thin it would make a layer 3 mm thick shields life from the Sun's ultraviolet. See how chlorine tore a hole in it each spring.

The water cycle

The rain on a mountain was seawater about a week before. Follow one droplet up into a cloud and back, and see why a warmer sea makes heavier rain.

Tsunamis

A tsunami crosses the open ocean as fast as a jet, yet barely a metre high. Why does the same wave rear up and flood the land at the coast?

Volcanoes

Hawaii's volcanoes pour out rivers of lava, while Mount St Helens blew itself apart. What decides how a volcano erupts?

Life

50 articles

Animal reproduction

A cod lays a million eggs; a red deer has one calf. Yet each leaves about as many grown young. Follow four broods from birth to adulthood.

Antibiotic resistance

A drug that cleared an infection last year can fail this year. Dose a colony and watch the few resistant cells survive and take over in days.

Bacteria

One bacterium in warm broth can become millions by morning. Open one up, watch it split in two, and see why penicillin makes it burst.

Body systems

Your heart, lungs, gut and nerves never stop working, and none can work alone. See how eleven organ systems share the job of keeping one body alive.

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Breathing and gas exchange

You take about 20,000 breaths a day. Follow one down to an air sac to see how oxygen gets into your blood, and why mountain air leaves you breathless.

Cancer

Your cells divide billions of times a day and almost never go wrong. Add mutations one at a time and watch the controls fail until a lump grows and spreads.

Cell division

Your body makes millions of new cells every second. Step through a dividing cell to see how it copies, sorts and splits its chromosomes.

Cells

Every living thing is built from cells, tiny bags of chemistry with the same working parts. Cut one open and look at what each part does.

Cellular respiration

Every breath you take feeds a furnace inside your cells. Follow one sugar molecule into a mitochondrion, then cut the oxygen and see what it costs.

Circulation

Your heart beats 100,000 times a day. Cut one open to see how four chambers and four valves drive blood round two loops, and why it races when you run.

CRISPR and gene editing

A bacterial protein can cut DNA at one chosen spot among billions of letters. How does Cas9 find its target, and how does a cut change a gene?

Cycles of matter

Life has used the same atoms for billions of years. Follow carbon and nitrogen round a meadow for a year, then stop the rot and watch the cycle jam.

Diffusion and osmosis

Molecules wander at random, yet sugar spreads out and water climbs through membranes. See how random motion moves water into cells or out of them.

Digestion

A meal is eaten in minutes but digested over hours. Follow one from mouth to colon to see how food gets small enough to pass into your blood.

Ecosystems and population dynamics

Rabbits multiply, then the foxes that eat them do, then both crash. See why predator and prey go round the same loop, and what sets its average.

Embryonic development and stem cells

Every body starts as one cell. Follow its first four weeks, from a hollow ball to layers to a body, as its cells narrow what they can become.

Enzymes

Chew bread for a while and it starts to taste sweet. Enzymes, life's protein catalysts, are at work, but only within a narrow window of warmth.

Epidemics and the SIR model

One ill person in a crowd can start an outbreak that reaches most of it, or none. One number, R₀, says which, and how many must be immune to stop it.

Feeding strategies

A cow grinds, a cat slices, a whale strains the sea. See how teeth, beaks, tongues and guts are shaped by what an animal eats and how it gets it.

Flocking and collective behaviour

Thousands of starlings swirl at dusk like one creature, yet no bird is in charge. How does a flock steer itself with no leader?

Food chains

A heron eats fish that ate smaller fish that ate plankton. Follow a lake's energy up the chain and see why so little of it reaches the top.

From DNA to protein

A gene is a string of letters, but a cell runs on proteins. Watch one gene get copied, read and folded, then change a single letter.

Fungi

Mushrooms pop up overnight after rain. Wash the soil away to see the fungus they grow from, a web of threads that rots leaves and feeds trees.

Genetics and DNA

A twisted ladder of four letters carries the instructions for every living thing. Change the mix, then unzip it and watch it copy itself.

Habitats and biomes

Rainforest, desert or tundra? A place's temperature and rainfall go a long way to deciding what grows there. See how, and why the rain alone is not enough.

Hearing

A whistle and a bass drum reach the same small ear. How does a coiled tube of fluid tell one pitch from another and pass it to the brain?

Homeostasis

Walk from a frosty street into a heatwave and your core stays within a degree of 37 °C. See how a thermostat in your brain holds it there.

Hormones and the endocrine system

Eat a bowl of pasta and your blood sugar hardly moves. See how two hormones from the pancreas tell the liver and muscles to hold it steady.

Immune system and vaccines

The first time a virus gets in, your body needs a week to answer it. A vaccine is a rehearsal, so the real meeting is over before you feel ill.

Inheritance and Punnett squares

Two purple pea plants can have white-flowered young. Cross them, fill in the Punnett square, then count seedlings until the 3 to 1 ratio appears.

Locomotion

A dog pushes the ground, a trout the water, a pigeon the air. Speed each one up to see what pushes back, and what every metre costs.

Metamorphosis

A caterpillar becomes a butterfly and a tadpole a frog. Watch one change day by day, cut it open, and find out what tells it when to change.

Microscopic life

A drop of pond water looks empty, yet it is full of hunters and grazers. Zoom in from the whole drop to 1,000× and see how small each one is.

Movement and muscles

Your biceps pulls far harder than the weight in your hand. Load an arm, bend the elbow, then zoom into the muscle to watch its filaments slide.

Natural selection

Peppered moths turned black as soot darkened England's trees. Change the bark and the birds' appetite, and watch a population's colour evolve.

Nervous system

Your body runs on tiny electrical pulses racing along cells a metre long. Push a neuron past its threshold and watch a signal fire.

Nutrition

Food is fuel, building material and a few small helpers. Follow a day's carbohydrate, fat, protein, vitamins, minerals, water and fibre into the body.

Photosynthesis

Plants build themselves out of air, water and light. Cut open a leaf to see the factory, then starve it of light or carbon and watch it slow.

Plant reproduction

Every seed in a tomato or an apple began as one pollen grain landing on a flower. Follow the pollen down into the flower and watch the fruit grow around it.

Plant structure and tropisms

A plant on a windowsill leans towards the glass. Move the lamp or tip the box, and watch a seedling steer by growing one side faster than the other.

Plant transpiration

A tree lifts hundreds of litres of water a day with no pump. See how evaporating leaves pull it up, and why dry, sunny air pulls harder.

Proteins and folding

A protein is a chain that folds itself into one exact shape, and a little heat undoes it. Watch a chain collapse round its oily core, then melt it.

Senses

Touch, warmth, smell and sight all start the same way, with a cell that turns one kind of stimulus into nerve signals. Watch it happen in a fingertip.

The brain

Your brain is 2% of your weight and burns a fifth of your energy. See which parts light up when you look, listen, move or speak.

The fossil record

A fish dies on a Jurassic sea floor. Will anything of it last 183 million years? Watch it rot, sink into mud, turn to stone and weather out of a cliff.

The microbiome and symbiosis

Your colon holds about as many microbes as your body has cells. See what fibre does for them, and what they give you back in return.

Threatened species

Cut a forest into patches and its animals can vanish while trees still stand. See why small, cut-off groups die out, and what helps them recover.

Viruses

A virus is a packet of genes in a protein coat, far smaller than a bacterium. See how one breaks into a cell and turns it into a virus factory.

Vision

Your eye focuses by changing the shape of a lens. Move a card, try short and long sight and glasses, then zoom in to the cones the image lands on.

What is life

A candle flame feeds, breathes and grows. A virus does none of that, yet it evolves. Check six things against seven signs of life and see where life begins.

Technology and engineering

27 articles

Batteries

A phone battery runs all day and refills overnight. Open a lithium-ion cell and follow the lithium that carries its charge back and forth.

Cameras and image sensors

A camera turns light into numbers. Why does a wide aperture blur the background, a slow shutter smear motion, and a high ISO add grain?

Desalination

Seawater is everywhere and undrinkable. Press it against the right membrane hard enough and fresh water comes out. How hard is hard enough?

Electric motors

A fan, a drill and an electric car all turn because a current sits in a magnet's field. What pushes the coil round, and why does it never reverse?

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Electronics

Every phone and computer is built from billions of switches with no moving parts. Flip one with a small voltage and watch it light a bulb.

Engines

A car engine turns thousands of times a minute, pushed by burning fuel. How does a small fire in a metal cylinder become a turning wheel?

Feedback and control

Balancing a broom on your hand means watching it and moving all the time. Teach a motor to do it, and find out how hard it should push back.

Flight

A wing tilted slightly into the wind holds up a plane weighing tonnes. Watch smoke flow past a wing to see where lift comes from, and how it can vanish.

Fusion reactors

A fusion plasma is ten times hotter than the Sun's core. No wall can touch it, so a magnetic field holds it. Why does that field need a twist?

GPS

Your phone finds itself on a map to within a few metres, with no signal sent back. How do clocks 20,000 km up tell it where it is?

Hydraulics

In a garage, one push on a small pump lifts a car. Change the sizes of two pistons and see how oil multiplies a force, and what it charges for it.

Lasers

A torch beam spreads out in a few metres, but a laser's stays a thin bright line across a room. What makes laser light march in step?

Materials technology

Bend a paper clip and it stays bent; a carbon-fibre rod springs straight back. Pull five materials apart and see what each is doing inside.

Medical imaging

An X-ray squashes the whole body into one shadow. A CT scanner takes hundreds from all around and works out a single slice. How?

Microscopes

A light microscope shows bacteria but never the viruses on them, however much it magnifies. Why does light run out, and how do electrons see further?

Particle accelerators and detectors

The LHC is a 27-kilometre ring. Why does it have to be so big, and how does a detector tell which particles came out of a collision?

Refrigerators and heat pumps

Heat flows from hot to cold, yet a fridge keeps food cold in a warm kitchen. How does it push heat uphill, and why is the back warm?

Robotics

A factory robot arm puts each part on the same spot, every time. Turn its joints yourself, and see why its controller has to work backwards.

Rockets and spaceflight

A rocket the weight of a building lifts off to put a car-sized load in orbit. Why is a rocket almost all fuel, and why does it drop pieces on the way up?

Simple machines

A crowbar, a pulley and a bicycle's gears all let a small push move a heavy load. Try three machines and find the catch each of them hides.

Solar cells

A solar panel makes electricity with no fuel and no moving parts. Tilt one under the Sun and see how light pushes electrons round a circuit.

Sonar and echolocation

Shout at a cliff and the echo comes back late. Ships time echoes to map the seabed, so why can't one pitch show both fine detail and deep water?

Structures and bridges

A plank sags when you stand on it, yet a steel bridge carries lorries over a river. Four bridge shapes, one job. Where does the weight go?

Telecommunications

An old car radio hisses as you drive away from the station; a digital one plays perfectly, then cuts out. Why do they fail so differently?

Telescopes

Through a telescope, faint stars appear and one star splits into two. Is that magnification, or something else? Compare a lens and a mirror.

Transformers and the power grid

Power lines carry electricity across the country at hundreds of thousands of volts. Why not send it at the voltage the generator makes?

Wind turbines

A breeze barely turns a wind turbine, yet a gale makes it stop. Push the wind speed and see why its power rises so steeply, and where it has to be capped.

Computing and information

15 articles

3D graphics and ray tracing

Films and games draw 3D worlds by working out the colour of every pixel. How does following rays of light backwards from a camera make a picture?

Algorithms and sorting

Sorting eight blocks by hand is easy. Sorting a million takes a method. Why do some methods finish in a blink while others take hours?

Binary and logic gates

Every computer is built from switches that are either on or off. How can a handful of on-off switches do arithmetic?

Cellular automata and the Game of Life

Cells on a grid that only count their neighbours make blinkers, gliders and guns nobody designed. How can such a simple rule do so much?

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Cryptography

Everything you send online crosses wires that strangers can read. How can two people agree on a secret key while someone hears every word?

Digital images and colour

Zoom into any photo on a screen and it breaks into squares of colour. How few numbers can a picture be made of before you notice?

Error-correcting codes

Noise flips bits on every wire and radio link. How can a receiver find a wrong bit and fix it without asking for the message again?

How a CPU works

A processor only ever moves numbers between a few boxes, one clock tick at a time. So how does that add up to running a program?

Information and entropy

A fair coin flip is pure surprise; a rigged one barely tells you anything. Why does predictable data shrink when you compress it?

Large language models and attention

A chatbot writes its answer a word or part of a word at a time, each a guess at what comes next. How does it decide which earlier words matter?

Networks and the internet

A message to a server on the far side of the world arrives in a blink, even when cables break. How does it find its way?

Neural networks

Nobody writes the rules a neural network follows. It starts with random guesses and learns from examples. How does guessing turn into knowing?

Quantum computing

A qubit can be 0 and 1 at once, yet reading it gives only one bit. So how can a quantum computer find an answer faster than guessing?

Search and PageRank

A search engine finds thousands of pages with your words on them. Which should come first? Let the links between pages vote.

Turing machines and computability

A machine that only reads, writes and moves along a tape can compute whatever a computer can. Can it always tell whether a program will stop?

Mathematics

24 articles

Calculus: rates and areas

How steep is a curve at one point, and how much area lies under it? Narrow the slices and see how the two answers undo each other.

Chaos

Two pendulums released a hair apart swing as one, then suddenly go separate ways. Find out why some motion can never be predicted for long.

Complex numbers

Multiplying by i turns a point a quarter of the way round. Repeat any multiplication and it spirals, which leads straight to Euler's formula.

Conic sections

A planet's orbit, a thrown ball's arc and a dish antenna's curve are all slices of one cone. Tilt the cut and watch one shape turn into another.

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Exponential growth and logarithms

Doubling looks slow, then explosive. Stack up repeated growth, then switch to a log scale and watch the hockey-stick curve turn into a straight line.

Fibonacci spirals

Count the spirals in a sunflower and you nearly always get two numbers from the Fibonacci sequence. One angle explains why.

Fourier series

Spin circles on circles and the tip traces any repeating wave, even a square one. Add more circles and the corners sharpen, but each jump keeps a spike.

Fractals

A snowflake edge that grows longer forever but fences in a finite area. Zoom into a fractal and the same picture keeps coming back.

Functions and their graphs

A rule that turns each x into one y draws a picture. Push the three numbers of a parabola and see one quantity decide if it meets the axis.

Game theory

In a single game, betraying always pays more. So why do selfish players who meet again and again end up cooperating?

Graph theory

Can you stroll through a town crossing each of its bridges exactly once? In 1736 Euler settled it by counting, and graph theory began.

Higher dimensions

A flat creature can only know a cube by its shadow and its slices. Turn a four-dimensional cube and slice it, the way it would know ours.

Knots

Tie a knot in a rope and join the ends. Some tangles then fall apart with a little pulling; others never will. How can you tell which?

Non-Euclidean geometry

On paper a triangle's angles add up to 180°. Draw one on a ball or a saddle and they don't. Bend the surface and watch the sum change.

Platonic solids

Dice come in only five perfectly fair shapes. Press a corner flat, count corners, edges and faces, and see why a sixth can never exist.

Prime numbers

Wind the counting numbers into a spiral and the primes, which only 1 and themselves divide, fall into odd lines. How do you find them, and do they ever run out?

Probability and the bell curve

Drop one ball through a field of pegs and nobody can say where it lands. Drop hundreds and the same hump appears every time. Why?

Pythagoras and geometry

Put a square on each side of a right triangle and the two small ones exactly fill the big one. Slide the pieces across and see why.

Sequences and series

Add the same step each time and a staircase climbs in a straight line; multiply and it curves. Stack the steps to see when an endless sum has a total.

Statistics and regression

Twenty measurements scatter around a hidden rule. Find their middle and their spread, then the one line that misses them least, and how well it fits.

Symmetry

Snowflakes, starfish and floor tiles all repeat one shape by turning or reflecting it. Change the turns and mirrors and see which patterns can exist.

Topology and the Möbius strip

Give a paper loop a half-twist and it has only one side. Cut it down the middle and it stays in one piece. Topology explains why.

Trigonometry and the unit circle

A point going round a circle rises and falls, and swings left and right. Unroll those two motions and you get the sine and cosine waves.

Vectors and transformations

Every shape a computer draws is moved by a matrix. Push two arrows and the whole grid follows, and one number says how much every area changes.

Cross-cutting

8 articles

Bayesian reasoning and evidence

A 90% accurate test says you have a disease that 1 in 100 people have. The chance you do is far below 90%. Count a crowd of a thousand to see why.

Classifying life

Is a bat a kind of bird? Is a whale a fish? Sort eleven living things by looks, then rebuild the tree by shared ancestry and see who is kin.

Models and uncertainty

Time a falling ball and every drop gives a slightly different g. How sure is the average, and what error can no number of drops remove?

Scale of the universe

From an atom to a galaxy in six steps. Each stop is a world of its own, and every one of them is built from the one before.

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Scaling and the square–cube law

Make a table or an animal twice as big and it weighs eight times as much, but its legs are only four times as strong. See why giants need thick legs.

The scientific method

A good guess makes a prediction that could fail. Test three ideas about pendulums and see why one clear miss outweighs any number of agreements.

Timeline of life

Squeeze Earth's 4.5 billion years into one day and microbes have it to themselves until evening. We arrive in the last six seconds.

Units of measurement

One litre of water is 10 cm, 1000 cm³, 61 cubic inches and 1 kg all at once. What is a unit, and what fixes how big a metre is?

Learning by doing

A little less abstract.
A lot more “aha.”

Every ViewWiki article pairs an interactive 3D scene with a clear explanation. Start with what you can see, experiment with what you can change, then connect the pieces. Curiosity does the rest.