HoW

The observable universe has a diameter of about 93 billion light-years and contains an estimated 2 trillion galaxies. Despite being 13.8 billion years old, the expansion of space makes it much larger.

Earth rotates at about 1,670 km/h at the equator, completing one full rotation every 23 hours, 56 minutes, and 4 seconds (a sidereal day). The rotation is gradually slowing.

A human can typically survive 3–5 days without water under normal conditions. The brain is 75% water, and just 2% dehydration impairs cognitive function. Temperature and exertion shorten this dramatically.

An adult human has 206 bones. Babies are born with approximately 270 bones, but many fuse together during growth. The smallest bone is the stapes (stirrup) in the ear — just 3 mm long.

Military submarines typically operate at ~300–600 meters. The deepest crewed dive reached 10,928 meters — the DSV Limiting Factor piloted by Victor Vescovo in the Mariana Trench in 2019.

GPS uses a constellation of 24+ satellites that each broadcast precise time signals. Your device calculates its distance from at least 4 satellites via signal travel time, determining your position to within 1 meter.

The Sun is approximately 4.603 billion years old — nearly halfway through its main-sequence lifetime. It will continue fusing hydrogen for another ~5 billion years before expanding into a red giant.

Only about 20% of the ocean floor has been mapped to high resolution, and far less has been directly explored. The ocean covers 71% of Earth's surface and contains 97% of all water on the planet.

Airplanes fly because their wings generate lift — the shape and angle of the wing push air downward, and the air pushes the wing up, overcoming gravity.

The internet breaks data into small packets that travel across a global web of cables and routers, reassembling at the destination using shared protocols like TCP/IP.

Vaccines train your immune system by showing it a harmless piece or version of a germ, so it can recognize and fight the real infection quickly if you are exposed.

Glass is made by melting sand (silica) with soda ash and limestone at about 1,700°C, then cooling the molten mixture quickly so it hardens without crystallizing.

Batteries store energy chemically and release it as electricity through reactions that push electrons from one terminal to the other via an external circuit.

A microwave oven heats food by bombarding it with microwaves that make water molecules vibrate rapidly, and that molecular motion is heat generated throughout the food.

Rainbows form when sunlight enters raindrops, bends, reflects off the back, and splits into its colors. You see them when the Sun is behind you and rain ahead.

The heart is a muscular pump with four chambers that pushes blood through the body, beating about 100,000 times a day to deliver oxygen and remove waste.

Earthquakes happen when stress built up along faults in Earth's crust is suddenly released, sending out seismic waves that shake the ground.

Nuclear power splits heavy atoms like uranium in a chain reaction, releasing enormous heat that boils water into steam to spin turbines and generate electricity.

Plants make food through photosynthesis, using sunlight, water, and carbon dioxide to produce sugar and release oxygen.

The brain works through billions of nerve cells that pass electrical and chemical signals, forming the networks behind thought and memory.

Tides are caused mainly by the Moon gravity pulling on Earth oceans, creating bulges of water that rise and fall as the planet rotates.

A refrigerator keeps food cold by pumping a special fluid around a loop that absorbs heat from inside and releases it outside.

Muscles work by contracting — their fibres slide together to shorten the muscle, pulling on bones to create movement.

Wi-Fi sends data through the air using radio waves, letting devices connect to the internet without cables.

We hear when sound waves enter the ear, vibrate the eardrum, and are converted into nerve signals the brain interprets as sound.

A camera captures an image by focusing light through a lens onto a sensor or film that records the pattern of light.

Digestion breaks food down into nutrients the body can absorb, as it travels through the mouth, stomach, and intestines.

Magnets work because the electrons in certain materials align, creating a magnetic field that attracts or repels other magnetic objects.

The Sun produces energy through nuclear fusion, fusing hydrogen into helium in its core and releasing enormous amounts of light and heat.

Clouds form when warm, moist air rises and cools, causing water vapour to condense into tiny droplets around dust particles.

Most modern touchscreens sense the tiny electrical charge in your finger, detecting exactly where you touch the glass.

The heart pumps blood in a continuous loop, delivering oxygen and nutrients to the body and returning to collect more oxygen from the lungs.

A compass works because its magnetised needle aligns with Earth magnetic field, pointing toward the magnetic north pole.

Magma rises from deep within the Earth when pressure builds, eventually breaking through the surface as lava, ash, and gas.

Birds navigate using a combination of the Sun, stars, Earth magnetic field, landmarks, and even smell to travel thousands of kilometres between breeding and wintering grounds.

A nuclear reactor generates energy by sustaining a controlled chain reaction of uranium fission, using the heat to produce steam that drives turbines.

Holograms record the interference pattern between a reference laser beam and light reflected from an object, reconstructing a 3D image when illuminated.

Electric cars use rechargeable lithium-ion battery packs to power electric motors that drive the wheels, replacing the internal combustion engine.

3D printing builds objects layer by layer from a digital model, depositing or fusing material one thin slice at a time.

Antibodies are Y-shaped proteins produced by B cells that bind to specific antigens on pathogens, marking them for destruction by the immune system.

Sonar sends sound pulses through water and measures the echoes that bounce back from objects to determine their distance and location.

Cone cells in the retina contain pigments sensitive to red, green, or blue light; the brain combines their signals to perceive the full spectrum of colours.

Steel is made by heating iron ore in a blast furnace and then refining the molten iron by reducing its carbon content to between 0.2% and 2.1%.

Photovoltaic (PV) solar panels convert sunlight directly into electricity using semiconductor materials that release electrons when struck by photons.

An airplane generates lift because the wing shape and angle deflect air downward, and by Newton third law, the air pushes the wing upward.

Glaciers form when accumulated snow compresses over decades into dense ice that begins to flow under its own weight.

Memory foam is a viscoelastic polyurethane that softens with body heat, moulding to your shape, then slowly returns to its original form when pressure is removed.

Carbon dating measures the remaining radioactive carbon-14 in organic material; since C-14 decays at a known rate, the amount left reveals the age.

Hurricanes form over warm tropical oceans when moist air rises, creating a low-pressure centre that organises into a rotating storm.

A laser produces an intense, coherent beam of light by stimulating atoms to emit photons in phase, through a process called stimulated emission.

Vaccines train the immune system by exposing it to a harmless version of a pathogen, prompting it to produce antibodies and memory cells.

Submarines control their buoyancy by flooding ballast tanks with seawater to dive and blowing compressed air into the tanks to surface.

Trees communicate through underground fungal networks ("wood wide web"), chemical signals in the air, and root-to-root contact.

Radar emits radio waves that bounce off objects; by measuring the time, direction, and frequency shift of the return signal, it determines distance, position, and speed.

MRI uses powerful magnets and radio waves to align and then detect hydrogen atoms in the body, creating detailed images of soft tissues.

Seeds germinate when water, warmth, and (sometimes) light trigger the embryo inside to break dormancy, absorb water, and grow a root and shoot.

Stellar black holes form when a massive star exhausts its nuclear fuel and its core collapses under gravity to an infinitely dense point.

Different metal salts produce specific colours when heated: strontium for red, barium for green, copper for blue, and sodium for yellow.

Tectonic plates move due to convection currents in the mantle, slab pull at subduction zones, and ridge push at mid-ocean ridges.

Miners use powerful computers to solve complex mathematical puzzles; the first to solve one validates a block of transactions and earns newly minted cryptocurrency.

The immune system uses two lines of defence: innate immunity (fast, general barriers and cells) and adaptive immunity (targeted antibodies and memory cells).

Chocolate is made by fermenting, roasting, and grinding cacao beans into cocoa mass, then mixing with sugar and cocoa butter.

Encryption converts readable data into scrambled ciphertext using a mathematical algorithm and a key; only someone with the correct key can decrypt it back.

Solar panels convert sunlight directly into electricity using the photovoltaic effect — photons from sunlight knock electrons free in semiconductor material (usually silicon), creating an electrical current.

A pin tumbler lock contains spring-loaded pins of varying lengths; when the correct key is inserted, its ridges push each pin to exactly the right height to align at the "shear line," allowing the cylinder to rotate and open the lock.

Tsunamis travel at speeds proportional to the square root of ocean depth — in deep ocean (4 km deep), they move at about 720 km/h (the speed of a jet airliner), because the entire water column from surface to seafloor participates in the wave.

Active noise-cancelling (ANC) headphones use tiny microphones to detect ambient sound and instantly produce an "anti-noise" signal — a sound wave that is the exact opposite (180 degrees out of phase), which destructively interferes with the noise and cancels it.

A magnetic compass needle is a small magnet that aligns itself with Earth magnetic field — since the field lines run roughly north-south, the needle north-seeking pole points toward Earth magnetic north.

Coral reefs form over thousands of years as tiny coral polyps secrete calcium carbonate skeletons that accumulate layer upon layer; symbiotic algae (zooxanthellae) living inside the polyps provide most of the energy needed for this construction.

Nuclear weapons release enormous energy through uncontrolled nuclear fission (splitting heavy atoms like uranium-235 or plutonium-239) or a combination of fission and fusion (thermonuclear/hydrogen bombs), converting a small amount of mass directly into energy via E=mc2.

Electric eels generate electricity using specialised cells called electrocytes — thousands of disc-shaped cells stacked like batteries in series, each producing a small voltage that combines to deliver shocks of up to 860 volts.

General anaesthesia renders patients unconscious by disrupting neural signalling in the brain — anaesthetic drugs enhance inhibitory neurotransmission (mainly via GABA receptors) or block excitatory signalling, though the exact mechanism of unconsciousness is still not fully understood.

Geysers erupt when underground water heated by magma reaches boiling point under pressure in a narrow, constricted plumbing system — a chain reaction of steam formation rapidly expels the water column in a spectacular jet.

Carbon capture and storage (CCS) involves capturing CO2 from industrial emissions or directly from the atmosphere, compressing it, and storing it underground in geological formations to prevent it from contributing to climate change.

Chameleons change colour by actively tuning nano-crystals in specialised skin cells called iridophores — by spacing these crystals closer or farther apart, they change which wavelengths of light are reflected.

Bluetooth uses short-range radio waves in the 2.4 GHz ISM band to wirelessly connect devices, rapidly hopping between 79 channels 1,600 times per second to avoid interference from other devices using the same frequency band.

Desalination removes salt and minerals from seawater to produce fresh water, primarily using reverse osmosis (forcing water through semi-permeable membranes under high pressure) or thermal distillation (boiling and condensing water vapour).

Antibiotics kill bacteria or stop their growth by targeting essential processes unique to bacterial cells — such as cell wall synthesis, protein production, DNA replication, or metabolic pathways — while ideally leaving human cells unharmed.

3D printers build objects layer by layer from a digital model, typically by extruding melted plastic filament (FDM), curing liquid resin with UV light (SLA), or fusing powder with a laser (SLS) — a process called additive manufacturing.

A thermos (vacuum flask) keeps liquids hot or cold by minimising all three modes of heat transfer: a vacuum between double walls eliminates conduction and convection, while reflective surfaces reduce radiation.

Freeze-drying (lyophilisation) preserves materials by freezing them solid, then reducing the surrounding pressure so the frozen water sublimates directly from ice to vapour, bypassing the liquid phase entirely and leaving a dry, lightweight product that retains its original structure.

A heat pump moves heat from a cooler space to a warmer one using a refrigeration cycle — compressing and expanding a refrigerant fluid to absorb heat outside and release it inside, achieving 300-500% efficiency because it moves heat rather than generating it.

Most bats navigate using echolocation: they emit high-frequency ultrasonic calls (typically 20-200 kHz) and listen for the returning echoes to build a detailed "sound map" of their surroundings, detecting objects as thin as a human hair.

Car airbags deploy in about 20-30 milliseconds: crash sensors detect sudden deceleration, triggering an electrical signal to an inflator that ignites a chemical propellant (sodium azide), rapidly generating nitrogen gas that fills the nylon bag.

Oxygen is produced as a byproduct of the light reactions of photosynthesis, when chlorophyll absorbs light energy and uses it to split water molecules (H2O), releasing O2 and freeing electrons and hydrogen ions to power sugar synthesis.

Bridges transfer the load of traffic and their own weight to the ground through structural elements that manage two fundamental forces: compression (pushing together) and tension (pulling apart), using designs like beams, arches, suspension cables, and trusses.

A microwave oven uses a magnetron to generate electromagnetic waves at 2.45 GHz that cause water molecules in food to rapidly oscillate, converting electromagnetic energy into thermal energy through molecular friction.

Fingerprints form during fetal development (around weeks 10-17 of pregnancy) when basal skin cells grow faster than the surrounding layers, buckling into the unique ridge patterns of loops, whorls, and arches that persist for life.

Stephen Hawking theorised in 1974 that black holes slowly lose mass and energy through Hawking radiation — quantum effects near the event horizon create particle-antiparticle pairs, with one falling in and the other escaping, gradually shrinking the black hole over unimaginably long timescales.

Plants sense gravity through specialised cells called statocytes, which contain dense starch granules (statoliths) that settle downward under gravity, triggering asymmetric distribution of the hormone auxin that directs roots downward and shoots upward.

A catalytic converter uses precious metals (platinum, palladium, rhodium) coated on a honeycomb ceramic substrate to catalyse chemical reactions that convert toxic exhaust gases (CO, NOx, hydrocarbons) into less harmful CO2, N2, and water vapour.

CRISPR-Cas9 uses a guide RNA to direct the Cas9 protein to a specific DNA sequence, where it makes a precise double-strand cut; the cell natural repair mechanisms then either disable the gene or allow insertion of new DNA.

A spinning gyroscope maintains its orientation due to conservation of angular momentum — the faster it spins, the more it resists changes to its axis of rotation, a property exploited for navigation, stabilisation, and inertial guidance.

Vaccines expose the body to a harmless piece of a germ so the immune system learns to fight it.

GPS receivers time signals from multiple satellites and use the delays to triangulate position.

Batteries store energy chemically and release it as electricity through controlled reactions.

The Sun evaporates water, which condenses into clouds and falls as rain, then flows back to the sea.

Plants release oxygen as a by-product of photosynthesis, splitting water using sunlight.

A refrigerator moves heat out of its interior by evaporating and compressing a refrigerant.

Tsunamis form when underwater earthquakes or landslides suddenly displace huge volumes of water.

Sound travels as vibrations that ripple through air, water or solids as pressure waves.

Most modern touchscreens sense the tiny electrical change your finger makes on a charged grid.

A jet engine sucks in air, compresses and burns it with fuel, and blasts hot gas out the back for thrust.

Wings generate lift by deflecting air downward and creating lower pressure above the wing.

Microwaves make water molecules in food vibrate rapidly, generating heat from within.

Solar panels convert sunlight into electricity when light knocks electrons loose in silicon cells.

Blood clots when platelets plug a wound and proteins weave a fibrin mesh to seal it.

A hologram records the interference pattern of laser light to recreate a 3D image.

A 3D printer builds a solid object layer by layer from a digital design, most commonly by melting plastic and depositing it in thin successive layers that fuse and harden into the final shape.

A battery stores energy in chemical form and converts it to electricity through reactions that push electrons from one terminal to the other through a circuit.

A typical car engine burns fuel and air in cylinders to create small controlled explosions that push pistons, and this up-and-down motion is converted into the rotation that turns the wheels.

A traditional hard drive stores data as tiny magnetised regions on spinning metal disks, with a read-write head magnetising and detecting these spots to record and retrieve information as binary code.

A hydroelectric dam generates electricity by using the force of falling or flowing water to spin turbines, which drive generators that convert the motion into electrical power.

A microwave oven cooks food by emitting microwaves that make water molecules in the food vibrate rapidly, and this molecular motion generates heat throughout the food.

A parachute works by dramatically increasing air resistance, creating enough drag to slow a falling person or object to a safe landing speed.

A rainbow forms when sunlight enters raindrops and is bent, reflected inside, and split into its component colours, which spread out to create an arc of colour in the sky.

A seismograph detects and records ground shaking from earthquakes by using a suspended mass that stays relatively still while the ground and instrument move around it, tracing the motion.

A solar panel converts sunlight directly into electricity using photovoltaic cells, in which light knocks electrons loose in a semiconductor material, creating an electric current.

A submarine dives and surfaces by changing its buoyancy, filling ballast tanks with water to sink and forcing the water out with compressed air to rise.

A vaccine trains the immune system to recognise and fight a specific germ by exposing the body to a harmless version or piece of it, so the body can respond quickly if it meets the real threat later.

A wind turbine generates electricity by using the wind to turn large blades, which spin a shaft connected to a generator that converts the rotation into electrical power.

Anesthesia works by using drugs to block nerve signals, either numbing a specific area or, in general anesthesia, causing a reversible, controlled loss of consciousness so a patient feels no pain during surgery.

Echolocation works by producing sounds and listening to the echoes that bounce back from objects, using the timing and direction of those echoes to build a mental map of the surroundings.

Airplanes stay up because their wings generate lift, an upward force created as air flows over and under the wing at high speed.

Honeybees communicate mainly through a waggle dance and through chemical scents, telling each other where to find food.

Most black holes form when a very massive star runs out of fuel and collapses under its own gravity at the end of its life.

Most large caves form as slightly acidic water slowly dissolves soluble rock such as limestone over thousands or millions of years.

Natural diamonds form deep inside the Earth under extreme heat and pressure, then are carried toward the surface by volcanic eruptions.

Fish breathe by passing water over their gills, which extract dissolved oxygen from the water and pass it into the blood.

Glaciers move slowly downhill under their own weight, sliding on meltwater at their base and deforming internally like a very slow, thick fluid.

Muscles grow when exercise causes tiny damage to muscle fibres, which the body then repairs and reinforces, making the fibres thicker over time.

The northern lights form when charged particles from the Sun collide with gases high in Earth atmosphere, making them glow.

A pearl forms when an irritant gets inside an oyster or mussel, which then coats it with layer after layer of a smooth substance called nacre.

Satellites stay in orbit by moving sideways so fast that they continually fall toward Earth while the planet curves away beneath them.

Spiders spin webs by producing liquid silk from glands in their abdomen and drawing it out through nozzles called spinnerets, where it hardens into thread.

Tornadoes form within powerful thunderstorms when rising warm air and changing winds set the air spinning into a violent, funnel-shaped column.

Volcanoes form where molten rock from deep inside the Earth rises to the surface, usually at boundaries between tectonic plates or over hotspots.

Camels survive long periods without water by storing fat in their humps, tolerating big changes in body temperature, and losing very little water.

Plants draw water up from the soil through their roots and lift it to the leaves mainly by the pull created as water evaporates from the leaves.

Seeds sense gravity, so roots grow downward and shoots grow upward, using special cells and plant hormones to guide the direction.

Snakes swallow prey much larger than their heads because their jaws are loosely connected and can spread wide apart, letting them walk their mouth over the meal.

Rivers carve canyons by slowly eroding rock with the force of flowing water and the grit and stones it carries, cutting downward over millions of years.

Waterfalls usually form where a river flows over a band of hard rock lying above softer rock, which erodes faster and leaves a steep drop.

Health authorities suggest a total daily water intake of about 3.7 litres for men and 2.7 litres for women, including water from food.

Adults need at least 7 hours of sleep a night, teenagers 8 to 10 hours and school-age children 9 to 12 hours.

There are 195 countries in the world: 193 United Nations member states plus 2 observer states, the Holy See and Palestine.

The Moon is on average about 384,400 kilometres from Earth, a distance light covers in about 1.3 seconds.

The Sun is on average about 149.6 million kilometres from Earth, a distance called one astronomical unit.

Earth is about 4.54 billion years old, based on radiometric dating of meteorites and ancient rocks.

The body breaks stored fat into fatty acids and glycerol and burns them for energy, releasing most of the mass as carbon dioxide you breathe out.

A credit card lets you borrow money from a bank to pay for purchases, which you repay later, with interest if you do not pay the full balance on time.

Search engines crawl the web with automated bots, store pages in a giant index, and rank results using hundreds of signals.

Facial recognition detects a face, measures its unique features, turns them into a mathematical faceprint and compares it with stored faces.

Self-driving cars use cameras, radar and lidar to sense their surroundings, and AI software to predict what others will do and plan a safe path.

A pregnancy test detects the hormone hCG, which the body starts producing after a fertilised egg implants in the uterus.

Hurricanes are named from rotating alphabetical lists set by the World Meteorological Organization, with names of very destructive storms retired.

US presidents are chosen by 538 electors allocated to states, and a candidate needs 270 electoral votes to win.

A polygraph records blood pressure, pulse, breathing and skin sweat, assuming that lying causes stress, but it cannot directly detect lies.

Alcohol is absorbed into the blood, slows the brain by boosting calming signals, and is broken down by the liver at about one standard drink per hour.

Sunscreen uses mineral or chemical filters to reflect or absorb ultraviolet rays before they can damage skin cells.

A trip to Mars usually takes about seven months, depending on the planets positions and the spacecraft route.

An octopus has three hearts: two pump blood through the gills and one pumps it around the rest of the body.

Daylight saving time moves clocks forward one hour in spring and back one hour in autumn to shift daylight into the evening.

About 8.2 billion people live on Earth, according to United Nations estimates for 2025; the world passed 8 billion on 15 November 2022.

Around 7,100 living languages are spoken today, according to Ethnologue, though about 40 percent are endangered.

Astronomers estimate the observable universe holds roughly 200 billion trillion stars, or about 2 followed by 23 zeros.

Most dogs live 10 to 13 years; the idea that one dog year equals seven human years is a myth, since dogs age much faster early in life.

Around 7,000 to 8,000 steps a day gives most of the health benefits; the famous 10,000-step goal began as a 1960s Japanese marketing slogan.

Adults usually have 32 permanent teeth, including four wisdom teeth, while children have 20 baby teeth.

An average adult has about 5 litres of blood, making up roughly 7 to 8 percent of body weight.

An average adult has about 30 to 37 trillion human cells, plus a similar number of bacterial cells living mostly in the gut.

An air conditioner pumps heat out of a room by circulating a refrigerant that absorbs heat indoors as it evaporates and releases it outdoors as it condenses.

Tattoo needles place ink in the dermis, the skin layer below the surface, where immune cells capture the pigment and hold it in place for years.

They read hundreds of thousands of genetic markers from your saliva and compare them with reference groups and other customers to estimate origins and find relatives.

Scalp hair grows about 1 to 1.25 centimetres per month, or around 15 centimetres a year.

A black box is actually two bright orange recorders, one storing flight data and one recording cockpit sounds, built to survive crashes and help investigators.

The Sun’s surface is about 5,500 degrees Celsius, while its core reaches about 15 million degrees Celsius.

ChatGPT is a large language model that predicts the next word-piece in a sentence, trained on vast amounts of text and then fine-tuned with human feedback.

UK health guidelines suggest about 2,000 kilocalories a day for an average woman and 2,500 for an average man, though needs vary with age, size and activity.

Fingernails grow about 3.5 millimetres a month on average, while toenails grow much more slowly, at about 1.6 millimetres a month.

For most healthy adults, health agencies such as the US FDA and the European Food Safety Authority say up to 400 milligrams of caffeine a day is safe.

The best-known scientifically observed record is 264 hours, about 11 days, set by 17-year-old Randy Gardner in San Diego in 1963–64.

A calculator turns each key press into binary numbers, then uses tiny electronic switches called transistors, arranged as logic gates, to add, subtract, multiply and divide.

Most elevators in tall buildings hang from steel ropes that run over a motor-driven wheel, balanced by a heavy counterweight on the other side.

X-rays are high-energy light waves that pass easily through soft tissue but are absorbed by dense materials such as bone, creating a shadow image on a detector.

A barcode stores numbers as a pattern of black bars and white spaces of different widths, which a scanner reads by measuring reflected light.

A marathon is 42.195 kilometres, or 26.2 miles, a distance officially standardised in 1921.

The Population Reference Bureau estimates that about 117 billion humans have been born since modern humans appeared around 200,000 years ago.

Earth’s mass is about 5.97 × 10²⁴ kilograms, or roughly 6 septillion kilograms.

About 1.3 million Earths could fit inside the Sun by volume.

Soap molecules pry apart the fatty outer layers of many germs and trap dirt and microbes in tiny bubbles called micelles, which rinse away in water.

Ships float because their hulls push aside a weight of water equal to their own weight, a rule known as Archimedes’ principle.

Rockets push hot exhaust gas downwards at great speed, and by Newton’s third law the rocket is pushed upwards, climbing past the 100-kilometre Kármán line into space.

Birds fly by flapping wings shaped like aerofoils that create lift and thrust, helped by hollow bones, powerful chest muscles and feathers that form a smooth flight surface.

Dolphins sleep with one half of the brain at a time, keeping the other half awake so they can surface to breathe and watch for danger.

Many ants lay chemical trails called pheromones between food and the nest, and nestmates follow and reinforce the strongest trails.

Inside the chrysalis, the caterpillar breaks down much of its body into a cell-rich fluid and rebuilds itself as a butterfly using groups of cells called imaginal discs.

A snake flicks its forked tongue to collect scent particles and presses them to the Jacobson’s organ in the roof of its mouth, which analyses the chemicals.

Whales are mammals that breathe air through blowholes on top of their heads, surfacing to exhale and inhale quickly before diving again.

Maglev trains use powerful magnets to lift the train slightly above the track and to push it forward, removing wheel friction and allowing very high speeds.

A helicopter’s spinning rotor blades act as rotating wings that create lift, and the pilot tilts them to move in any direction, including hovering.

An escalator is a loop of linked steps pulled by chains driven by an electric motor, with guide tracks that flatten the steps at each end.

Burners heat the air inside the balloon, making it less dense than the cooler air outside, so the balloon rises like a bubble in water.

Most smartwatches shine green LED light into the skin and measure how much is reflected back, which changes as blood pulses through the vessels.

Contactless cards and phones use near-field communication (NFC), a short-range radio link of a few centimetres, to send a one-time encrypted code to the payment terminal.

A speaker turns electrical signals into sound by using a magnet and a coil to vibrate a cone, which pushes air into pressure waves.

Fibre optic cables send data as pulses of light through thin glass strands, where total internal reflection keeps the light bouncing along the core over long distances.

Thermometers measure temperature using something that changes predictably with heat, such as a liquid expanding in a tube, a metal’s electrical resistance or infrared radiation.

A washing machine combines water, detergent, heat and mechanical movement of a rotating drum to loosen dirt, then spins at high speed to remove water.

A motor-driven fan creates low air pressure inside the vacuum, so higher-pressure air outside rushes in through the nozzle, carrying dust and dirt with it.

A lightning rod gives lightning a safe path to the ground through a thick conductor, so the current bypasses the building instead of causing fire or damage.

Geothermal power plants tap heat from deep underground, using hot water or steam to spin turbines that generate electricity.

Taste receptor cells in taste buds detect five basic tastes (sweet, sour, salty, bitter and umami) and send signals to the brain, which combines them with smell to create flavour.

Odour molecules bind to receptors in the upper nose, which send signals to the brain’s olfactory bulb, closely linked to areas for memory and emotion.

Broken bones heal in stages: a blood clot forms, then a soft callus of cartilage bridges the gap, hardens into bone and is slowly remodelled over months.

Common painkillers like ibuprofen and aspirin block enzymes that make pain-signalling chemicals called prostaglandins, while opioids act on receptors in the brain and spinal cord.

Each kidney contains around a million tiny filters called nephrons that remove waste and excess water from blood, producing urine.

When the diaphragm contracts, the lungs expand and draw in air; oxygen then passes through millions of tiny air sacs called alveoli into the blood, while carbon dioxide passes out.

The liver processes nutrients from digestion, filters toxins from the blood, makes bile to digest fats and stores energy, performing hundreds of vital jobs.

The average adult has about 100,000 hairs on their scalp, with the exact number depending largely on natural hair colour.

An average human heart beats roughly 2.5 to 3 billion times over a lifetime of about 80 years.

There is no exact figure, but the Oxford English Dictionary contains over 500,000 words and senses, and estimates of all English words reach about a million.

There are eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune; Pluto was reclassified as a dwarf planet in 2006.

Astronomers estimate the observable universe contains roughly 100 billion to 2 trillion galaxies, with most recent estimates in the hundreds of billions.

About 2 million species have been named, but scientists estimate there may be around 8.7 million species of plants and animals, and far more if microbes are included.

A 2015 study estimated there are about 3 trillion trees on Earth, roughly 400 for every person.

A 2022 study estimated there are about 20 quadrillion ants on Earth — roughly 2.5 million for every person.

Pet cats typically live about 12 to 18 years, and indoor cats often live longer than outdoor cats.

The ISS orbits Earth at about 28,000 km/h, circling the planet roughly every 90 minutes.

Deep space far from stars has a background temperature of about 2.7 kelvin, or roughly −270 °C, set by the cosmic microwave background.

A day on Mars, called a sol, lasts about 24 hours and 39 minutes, while a Martian year lasts about 687 Earth days.

Lava usually erupts at between about 700 °C and 1,200 °C, depending on its chemistry.

Snowflakes form when water vapour freezes onto a tiny particle in a cold cloud, growing into six-sided ice crystals whose shape depends on temperature and humidity.

Hail forms inside thunderstorms when strong updrafts carry raindrops high into freezing air, where they collect layers of ice until they are too heavy and fall.

Most mountains form when tectonic plates collide and push the crust upward, while others form from volcanic activity or blocks of crust rising along faults.

Islands form in several ways, including volcanic eruptions from the seabed, coral reefs growing on sunken volcanoes, and land separated from continents by rising seas.

Paper is made by breaking wood or recycled fibres into a watery pulp, spreading it into thin sheets, then pressing and drying them.

Cheese is made by curdling milk with bacteria and rennet, separating the solid curds from liquid whey, then pressing, salting and often ageing the curds.

Green coffee beans are soaked in water and then treated with a solvent, activated carbon filters or pressurised carbon dioxide to remove most of the caffeine before roasting.

Most plastic is made from oil and natural gas, which are refined into small molecules called monomers and then linked into long chains called polymers.

The pyramids were built by thousands of skilled paid workers using copper tools, ramps, sledges and levers to cut, move and place millions of stone blocks.

There are five named oceans: the Pacific, Atlantic, Indian, Southern and Arctic, though they all connect as one global ocean.

The most common answer is seven: Asia, Africa, North America, South America, Antarctica, Europe and Australia, but some countries teach five or six.