Science Mysteries
Pick a mystery. Have a guess before you peek: that guess is the whole point.
Showing 500 mysteries across 125 topics
Density & Floating
PhysicsWhether something floats depends on density, and you can come at that one idea from four different directions.
- 1
Why does ice float?
Tier 2 · water
- 2
Why does a giant steel ship float when a tiny coin sinks?
Tier 2 · water / forces / density
- 3
Why does a huge, heavy hot-air balloon rise into the sky?
Tier 2-3 · air / forces / density
- 4
Why do you float more easily in the sea than in a swimming pool?
Tier 2 · water / forces / density
Light & Colour
PhysicsLight travels in straight lines until it meets something, then it scatters, bends or splits, and that is where colour comes from.
States of Matter
ChemistryMatter moves between solid, liquid and gas as energy is added or taken away, and gases can even hide dissolved inside liquids.
How Your Body Works
The Human BodyYour body does a great deal without ever asking you: some of it keeps you balanced, some is left over from ancestors who needed it, and at least one of them nobody has explained yet.
Day, Night & Seasons
Earth & SpaceEarth's spin and its tilt, not how close we are to the Sun, create day, night and the changing seasons.
Meet the Microbes
MicrobiologyThe world is full of invisible living things, most harmless or helpful, a few harmful, and understanding them keeps us healthy and even feeds us.
Forces & Motion
PhysicsThings keep doing what they are doing until a force changes them, and how hard that change hits depends on how much motion there was and how quickly you take it away.
- 1
Why do you lurch forward when a car brakes?
Tier 2 · forces / motion
- 2
How can a magician whip a tablecloth away and leave the plates?
Tier 2-3 · forces / motion
- 3
Why do seatbelts and airbags save lives?
Tier 2-3 · forces / motion
- 4
Why is a lorry so much harder to stop than a bicycle?
Tier 2 · forces / motion
Acids & Bases
ChemistryAcids and bases are chemical opposites, measured on the pH scale, and cancelling one with the other explains a surprising amount of everyday life.
- 1
Why does lemon juice make a dull old coin shiny?
Tier 2 · acids / chemistry
- 2
Why do indigestion tablets make a sore tummy feel better?
Tier 2 · acids / chemistry
- 3
Why are fizzy drinks bad for your teeth?
Tier 2 · acids / chemistry
- 4
Why does red cabbage water change colour like magic?
Tier 2 · acids / chemistry
The Moon, Planets & Orbits
Earth & SpaceWatch the Moon and the planets closely and two things explain nearly everything: where the sunlight is falling, and the endless pull of gravity.
Plants & Photosynthesis
BiologyA leaf is a factory that builds a plant out of light, air and water, and almost everything else a plant does is arranged around keeping that factory supplied.
Heat & Temperature
PhysicsHeat flows from hotter things to cooler ones until everything matches, and on the way it makes materials feel different, swell, and refuse to stay hot.
- 1
Why does metal feel colder than wood, even in the same room?
Tier 1-2 · heat / conduction
- 2
How does one flask keep drinks hot AND cold?
Tier 2 · heat / insulation
- 3
Why do bridges and railway lines have gaps in them?
Tier 2 · heat / expansion
- 4
Why does a hot drink always go cold (and a cold drink warm up)?
Tier 1 · heat / energy
Sound
PhysicsSound is a wave travelling through the air: it has a speed, it bounces off surfaces, and its pitch shifts when the source moves.
Stars & the Sun
Earth & SpaceStars are distant suns making their own light, and that light carries their heat, their nature and their distance to us, though our own air muddles it on the way in.
Inside the Cell
BiologyEvery living thing is built of tiny cells, busy chemical factories that move water in and out, speed up reactions, and turn food into energy.
- 1
What is inside a single living cell?
Tier 1-2 · cells / biology
- 2
Why does a slug shrivel up when you put salt on it?
Tier 2 · cells / water / osmosis
- 3
What do enzymes actually do?
Tier 2-3 · cells / chemistry / enzymes
- 4
How does a single cell burn food to get the energy it runs on?
Tier 2-3 · cells / energy / respiration
Electricity & Magnetism
PhysicsElectric charge can sit still or flow, magnetism has a quiet pull of its own, and the deep surprise is that moving one of them conjures up the other.
Atoms & Elements
ChemistryEverything is built from about ninety kinds of atom, and how an atom's electrons are arranged decides how it behaves.
- 1
What is everything made of?
Tier 1-2 · atoms / elements
- 2
Why is the periodic table that funny shape?
Tier 2-3 · periodic table / electrons
- 3
What is it inside their atoms that lets gold shrug the world off when iron cannot?
Tier 2 · atoms / electrons / reactivity
- 4
Why are fireworks different colours?
Tier 2-3 · emission / electrons
Your Brain & Senses
The Human BodyWhat you see and feel is not raw reality but your brain's reading of the signals reaching it, which is why it can be fooled, surprised, or cut off altogether.
The Solar System
Earth & SpaceThe Sun's family of planets, moons and rubble each behave differently because of what they are made of and where they orbit, and that includes our own corner of it.
Genetics & DNA
BiologyYour features are written in DNA, a chemical code passed from your parents and shuffled, so you resemble them yet are unlike anyone else.
The Heart & Blood
The Human BodyYour heart pushes blood around a loop that never stops, and the blood itself, its colour, its leaks and its changing pace, quietly reports what the rest of you is doing.
Pressure & Flight
PhysicsAir and water are always pressing on everything, and differences in that pressure pop your ears, lift a plane and pull a drink up a straw.
- 1
Why do your ears pop on a plane or up a mountain?
Tier 1-2 · air pressure / altitude
- 2
How does a heavy plane stay up in the air?
Tier 2-3 · lift / air pressure
- 3
How does drinking through a straw actually work?
Tier 1-2 · air pressure / suction
- 4
Why does a vacuum cleaner suck things up?
Tier 2 · air pressure / suction
Energy
PhysicsEnergy is never created or destroyed, only passed on and changed from one form to another, and a little always escapes as heat.
- 1
Why is the first hill of a rollercoaster always the biggest?
Tier 2 · energy / motion
- 2
Why does a bouncing ball never bounce back as high?
Tier 1 · energy / motion
- 3
Why can't you build a machine that runs forever?
Tier 2-3 · energy / forces
- 4
Where does all the energy go when a car brakes?
Tier 2 · energy / motion
Weather & Climate
Earth & SpaceHeat and moving air drive our weather: the Sun warms the ground unevenly, water changes state, and the whole sky churns.
Evolution & Adaptation
BiologyLiving things change over generations to suit their world, because the individuals best matched to their surroundings survive to pass on their traits.
- 1
Why are polar bears white?
Tier 2 · evolution / adaptation
- 2
Why did peppered moths turn dark during the age of factories?
Tier 2-3 · evolution / adaptation
- 3
Why do we still have an appendix if we don't need it?
Tier 2-3 · evolution / the body
- 4
Why did cave fish lose their eyes?
Tier 2-3 · evolution / adaptation
Ecosystems & Food Chains
BiologyLiving things depend on each other and on the flow of energy, so what happens to one species ripples through them all.
- 1
Why are there far fewer lions than gazelles?
Tier 2 · ecosystems / energy
- 2
Why does everyone worry so much about bees?
Tier 2 · ecosystems / food chains
- 3
Why can removing one species wreck a whole food chain?
Tier 3 · ecosystems / food chains
- 4
Why are the biggest, fiercest predators always rare?
Tier 2-3 · ecosystems / energy
Mixtures & Solutions
ChemistryHow and why things dissolve (or refuse to), from salt on icy roads to oil that won't mix with water.
- 1
Why does sprinkling salt melt ice on the roads?
Tier 2 · mixtures / solutions
- 2
Why does sugar dissolve faster in hot tea than in iced tea?
Tier 1-2 · mixtures / solutions
- 3
Why won't oil and water mix?
Tier 2 · mixtures / solutions
- 4
How does soap wash away grease that water alone can't shift?
Tier 2-3 · mixtures / solutions
Friction & Grip
PhysicsFriction is the force that grips when surfaces touch: it lets us walk, slows us down, and turns motion into heat.
Why Water Is Special
ChemistryWater molecules cling to one another, and that clinginess explains how water climbs, beads up and holds an insect on its surface, while other liquids behave quite differently.
How a Tree Drinks
BiologyPlants pull water from their roots all the way to their highest leaves, with no pump, just clever physics.
- 1
How does water reach the top of a tall tree?
Tier 2-3 · plants / transport
- 2
Why do cut flowers droop after a few days?
Tier 2 · plants / transport
- 3
Why do leaves have veins running through them?
Tier 2 · plants / transport
- 4
Why does celery change colour when you stand it in dyed water?
Tier 1-2 · plants / transport
Bones & Muscles
The Human BodyYour skeleton is strong yet light, your joints decide how you can move, your muscles can only pull so they work in pairs, and your bones turn out to be alive and busy inside.
Black Holes & Dying Stars
Earth & SpaceStars don't last forever, and how they die, from quiet white dwarfs to blazing supernovae and black holes, shapes the whole universe.
Spinning & Balance
PhysicsSpinning things behave in ways that look like cheating, and working out why sometimes confirms that it is all about angular momentum and sometimes shows the real answer is something else entirely.
- 1
Why does a spinning skater speed up when they pull their arms in?
Tier 2-3 · spinning / motion
- 2
Why doesn't a moving bike fall over?
Tier 2-3 · spinning / balance
- 3
Why does a spinning top stay up when a still one falls over?
Tier 2-3 · spinning / balance
- 4
How do cats twist to land on their feet?
Tier 2-3 · spinning / motion
Your Microbiome
MicrobesYour body is home to trillions of tiny living things, most of them harmless or helpful partners you couldn't live without.
Breathing & Lungs
The Human BodyEvery breath swaps gases your body needs, and your lungs do it about 20,000 times a day without you even thinking.
Everyday Chemical Reactions
ChemistryBrowning apples, rusting iron, burning fuel and fizzing baking soda are all chemical reactions, atoms rearranging into something new.
Cell Division & Growth
BiologyYou grow and heal because your cells copy themselves and split in two, over and over, from a single starting cell.
Skin
The Human BodyYour skin is your biggest organ, a living, waterproof barrier that protects you, cools you and even makes vitamin D.
Eclipses & Shadows
Earth & SpaceWhen the Sun, Earth and Moon line up, one of them throws its shadow onto another, and watching that safely is a piece of science in itself.
Reflection & Mirrors
PhysicsLight bounces off surfaces by a simple rule, and that one rule explains reflections, the great left-right myth, curved mirrors, periscopes and kaleidoscopes.
- 1
Why can you see yourself in a mirror?
Tier 2 · physics / light
- 2
Why does a mirror swap left and right but not up and down?
Tier 2 · physics / light
- 3
Why are you the right way up in a flat mirror but a spoon flips you?
Tier 2 · physics / light
- 4
How do periscopes and kaleidoscopes work?
Tier 2 · physics / light
Vaccines & Fighting Infection
MicrobesYour body has a clever built-in defence team that learns to beat germs and remembers them, and vaccines give that team a safe head start that protects you and the people around you.
- 1
How does your body fight off germs that make you ill?
Tier 2 · microbes / immunity
- 2
Why don't you usually catch the same illness (like chickenpox) twice?
Tier 2-3 · microbes / immunity
- 3
How does a vaccine protect you without making you ill?
Tier 3 · microbes / immunity
- 4
How does protecting yourself help protect other people too?
Tier 3 · microbes / immunity
Seeds, Fruit & New Plants
BiologyA flowering plant makes new plants through one connected story: flowers swap pollen to make seeds, the flower's ovary swells into fruit around them, and the seeds then travel away to grow up somewhere new.
Crystals & Solids
ChemistryWhether a solid is a sparkling crystal, a super-hard diamond or a see-through pane of glass comes down to one thing: how its atoms are arranged, neatly stacked in a repeating pattern, or frozen in a jumble.
- 1
Why do crystals have such perfect flat faces and sharp edges?
Tier 2 · chemistry / solids
- 2
How does a salt or sugar crystal grow?
Tier 2 · chemistry / solids
- 3
Why is a diamond so hard but pencil 'lead' so soft, when both are pure carbon?
Tier 3 · chemistry / solids
- 4
Why isn't glass a crystal?
Tier 3 · chemistry / solids
Digestion
The Human BodyYour food goes on a journey through a long tube, getting broken down by muscles and chemicals so your body can soak up the goodness and tidy away the rest.
Pluto & Dwarf Planets
Earth & SpacePluto was not demoted by mistake: it turned out to be one of a crowd of round icy worlds beyond Neptune, and simply reaching any of them takes decades of patience.
Energy in Reactions
ChemistryEvery change moves energy in or out: pulling things apart costs energy and letting them join hands gives it back, and which way the sum lands decides whether you feel heat or cold.
- 1
Why do some reactions get hot, and others get cold?
Tier 2-3 · chemistry / energy
- 2
How does a hand-warmer get hot without any fire?
Tier 2-3 · chemistry / energy
- 3
How does an instant cold pack go cold on its own?
Tier 2-3 · chemistry / energy
- 4
Where does a reaction's heat actually come from, or go?
Tier 3 · chemistry / energy
Vision & the Eye
PhysicsYour eye is a living camera that focuses light onto the back of itself, and your brain then does the rest, correcting, sharpening and colouring whatever arrives.
Gravity & Falling
PhysicsGravity speeds everything up at the same rate wherever you stand, which is what makes falling feel the way it does; what changes from world to world is the strength of the pull, and what slows things down is the air.
- 1
Why do a feather and a hammer land together on the Moon?
Tier 2 · gravity / falling / air
- 2
Why does your stomach seem to lift on a rollercoaster drop?
Tier 2 · gravity / falling / forces
- 3
How can a thin sheet of fabric slow a falling person so much?
Tier 2-3 · gravity / falling / air
- 4
Why would you weigh less on the Moon but still be made of exactly the same stuff?
Tier 2 · gravity / mass / weight
Simple Machines
PhysicsA simple machine lets you swap a smaller push spread over a longer distance for a bigger force over a shorter one; it never gives free energy, it just rearranges the effort.
- 1
Why is it easier to walk up a long ramp than to climb straight up the same height?
Tier 1 · simple machines / forces
- 2
How can a small child lift a much heavier adult on a seesaw?
Tier 2 · simple machines / levers
- 3
Why does a long spanner loosen a stiff bolt when a short one will not budge it?
Tier 2 · simple machines / levers
- 4
How does a rope looped through pulleys let one person lift a very heavy load?
Tier 3 · simple machines / pulleys
Waves & Vibrations
PhysicsThings that wobble pass their energy on: a wave carries energy across water, string or air without carrying the stuff itself, and a well-timed push can build a wobble up.
- 1
Why do sea waves keep rolling in, when the water itself barely travels?
Tier 2 · waves / energy / oceans
- 2
Why does a plucked guitar string fill a room with sound?
Tier 2 · sound / waves / vibration
- 3
Why do ripples spread out in neat growing rings from a single dropped stone?
Tier 2 · waves / water / energy
- 4
Why does pushing a swing at just the right moment send it sky high?
Tier 2-3 · waves / resonance / motion
What Food Is Made Of
The Human BodyFood is both fuel and building material; carbohydrates, fats, proteins and tiny vitamins each do a different job inside you.
- 1
Why does a sugary snack give you a quick burst of energy, then a slump?
Tier 2 · carbohydrates / energy
- 2
Why does a buttery, fatty meal keep you full for hours?
Tier 2 · fats / digestion
- 3
Why do growing children and healing wounds both need protein?
Tier 2 · protein / growth
- 4
Why do you need some vitamins in only the tiniest amounts, yet cannot live without them?
Tier 2-3 · vitamins / health
Cleaning You From Inside
The Human BodyYour body constantly filters your blood and balances your water, keeping the useful parts and flushing out the waste and the extra.
- 1
What are your two kidneys quietly doing all day and night?
Tier 1-2 · kidneys / filtering / waste
- 2
Why is your pee yellow, and paler on some days than others?
Tier 1 · urine / pigments / hydration
- 3
Why do you suddenly need the toilet more when you get cold?
Tier 2-3 · blood flow / temperature / balance
- 4
Why does your body make you feel thirsty at exactly the right time?
Tier 2 · thirst / brain / water balance
Chemical Messengers
The Human BodyTiny chemical messengers called hormones travel in your blood to switch different parts of your body on and off, often without you noticing.
- 1
Why do you get grumpy and short-tempered when you're really hungry?
Tier 2 · hormones / body
- 2
Why do you start to feel sleepy soon after it gets dark?
Tier 2 · hormones / sleep
- 3
Why does your body slowly change as you grow from a child into an adult?
Tier 2-3 · hormones / growing up
- 4
Why do you actually do most of your growing while you're fast asleep?
Tier 2 · hormones / growth
The Fungus Kingdom
BiologyFungi are their own kingdom of life, neither plant nor animal; they feed by breaking other things down, which makes them both nature's recyclers and our helpers.
- 1
How does a spoonful of yeast make a whole lump of dough puff up?
Tier 1-2 · fungi / microbes
- 2
Why do mushrooms seem to pop up overnight after rain?
Tier 2 · fungi / life cycles
- 3
A mushroom cannot run and cannot make food from sunlight, so what on Earth is it?
Tier 2 · fungi / classifying life
- 4
How did a patch of mould turn into one of the greatest medicines ever?
Tier 2-3 · fungi / medicine
The Big Universe
Earth & SpaceThe universe is unimaginably huge, mostly empty space, and it is still stretching bigger every second.
- 1
A light-year sounds like a stretch of time, so why is it really a distance?
Tier 1 · space / distance / light
- 2
If space is packed with countless stars, why is the night sky mostly black?
Tier 2-3 · space / stars / light
- 3
What exactly is a galaxy, and where does ours fit in?
Tier 2 · space / galaxies / gravity
- 4
Is the whole universe really getting bigger, and if so, bigger into what?
Tier 3 · space / universe / expansion
The Restless Earth
Earth & SpaceEarth's hard surface is cracked into giant slabs that drift on the hot, soft rock beneath, and their slow grinding builds mountains, shakes the ground and feeds volcanoes.
- 1
Why does the solid ground suddenly shake in an earthquake?
Tier 2 · earth / earthquakes
- 2
Why does a mountain suddenly blast out red-hot rock?
Tier 2 · earth / volcanoes
- 3
How do towering mountains rise up from flat ground?
Tier 2 · earth / mountains
- 4
Why do the continents look like they could slot together like a jigsaw?
Tier 2-3 · earth / continents
Fossils & Deep Time
BiologyFossils are the preserved clues of ancient life turned to stone, and the layers of rock they sit in read like the pages of Earth's history book.
- 1
How does a soft, living animal end up as solid stone millions of years later?
Tier 2 · fossils / rock
- 2
Nobody ever saw a living dinosaur, so how do we know they were real?
Tier 1 · dinosaurs / fossils
- 3
Why are tall cliffs often made of neat stripy layers?
Tier 2 · rock / layers
- 4
How can scientists say a fossil is millions of years old?
Tier 2-3 · fossils / deep time
The Sun's Stormy Weather
Earth & SpaceOur calm-looking Sun is a churning ball of superhot gas with storms, dark spots and blasts of particles that can even paint lights across our night sky.
- 1
Why does the blazing Sun have dark spots on its face?
Tier 2 · space / sunspots
- 2
What is a solar flare, and why is it such a huge deal?
Tier 2-3 · space / solar flares
- 3
The Sun seems to just sit there, so how can it have a wind?
Tier 2-3 · space / solar wind
- 4
What makes the sky glow with green and pink northern lights?
Tier 2 · space / auroras
Everyday Materials
ChemistryWhether something bends, snaps, stretches, splits or lets light straight through comes down to how its insides are arranged and held together.
- 1
Why can you bend a metal spoon but a glass one would just snap?
Tier 2 · materials / metals
- 2
Why can you see straight through solid glass but not through a solid wall?
Tier 2-3 · materials / light
- 3
Why can you stretch a rubber band and it springs right back?
Tier 2 · materials / polymers
- 4
Why does wood split easily along its length but not across it?
Tier 2 · materials / wood
Circuits & Batteries
PhysicsElectricity does useful work only when it can flow all the way round a complete loop, and a battery is the pump that keeps it moving.
- 1
Why does a torch only work when everything is joined up just right?
Tier 1 · electricity / circuits
- 2
What is really going on inside a battery to make electricity flow?
Tier 2 · electricity / batteries / chemistry
- 3
How does invisible electricity turn into bright light in a bulb?
Tier 2 · electricity / light / heat
- 4
How can a tiny switch turn a whole light on and off?
Tier 1 · electricity / circuits / switches
Minibeasts & Metamorphosis
BiologyThe tiny creatures around us live astonishing lives, and some completely rebuild their bodies as they grow up.
- 1
How does a crawling caterpillar become a flying butterfly?
Tier 2 · minibeasts / metamorphosis
- 2
How does a spider spin such a perfect, sticky web from its own body?
Tier 2-3 · minibeasts / spiders
- 3
How do ants march in a perfect line straight to a dropped crumb?
Tier 2 · minibeasts / ants
- 4
Why do woodlice always scurry for the dampest, darkest corner?
Tier 2 · minibeasts / woodlice
How Animals Move
BiologyEvery animal's body is shaped for how it gets around, whether that is flying, swimming, climbing or slithering.
- 1
How does a heavy bird lift itself into the air and stay up?
Tier 2 · biology / birds / flight
- 2
How does a fish hang perfectly still in the water without sinking or rising?
Tier 2 · biology / fish / floating
- 3
How does a gecko run straight up a smooth wall and across the ceiling?
Tier 3 · biology / geckos / grip
- 4
How does a snake glide forward with no legs at all?
Tier 2 · biology / snakes / movement
Where Energy Comes From
PhysicsEvery scrap of electricity has to come from somewhere else first, and each source, from wind to buried fuel, arrives with its own long history and its own consequences.
- 1
How does a breezy day at a wind turbine end up as electricity in your home?
Tier 2 · energy / electricity
- 2
How does a flat black panel turn plain sunlight into electricity?
Tier 2-3 · energy / light
- 3
Where did the coal, oil and gas we burn actually come from?
Tier 2 · energy / fossil fuels
- 4
Why does burning fuels for energy end up heating the whole planet?
Tier 2-3 · energy / climate
Kitchen Science
ChemistryA kitchen is a laboratory: heating and cooling food rearranges what it is made of, sometimes permanently and sometimes only until you warm it up again.
- 1
Why does a runny egg turn firm and white when it heats up, and never turn back?
Tier 2 · food / proteins / heat
- 2
Why does pale bread turn golden-brown and smell delicious as toast?
Tier 2-3 · food / cooking / chemistry
- 3
Why does warm liquid jelly turn into a firm wobble in the fridge?
Tier 2 · food / molecules / cooling
- 4
Why does a hard little corn kernel explode into fluffy popcorn?
Tier 1-2 · food / heat / pressure
Colour & Mixing
PhysicsThe colour you see is simply the light that bounces back to your eye, which is why mixing paints and mixing lights follow opposite rules.
- 1
A red apple sits in plain white light, so where does the red come from?
Tier 1 · light / colour
- 2
Why does mixing lots of bright paints together give muddy brown?
Tier 2 · light / colour
- 3
How does a screen make every colour you can imagine from just red, green and blue?
Tier 2 · light / colour
- 4
Why do your clothes look the wrong colour under an orange street lamp?
Tier 3 · light / colour
Space Travel
PhysicsGetting to space, staying alive there and coming down again each need their own answer, and the machines we send up start earning their keep the moment they arrive.
- 1
There is nothing to push against in space, so how does a rocket move at all?
Tier 2 · physics / rockets
- 2
Why can't an astronaut just step outside the spacecraft in ordinary clothes?
Tier 1 · space / spacesuits
- 3
How do machines circling high above you help you every single day?
Tier 2 · space / satellites
- 4
Why is landing softly on the Moon so much harder than landing a plane?
Tier 2 · physics / moon landing
Sleep & Dreams
The Human BodySleep is not switching off; it is when your brain and body do vital repair, sorting and tidying that keep you healthy.
- 1
Why must you spend a third of your whole life fast asleep?
Tier 1 · body / sleep
- 2
Why does your mind play whole made-up films while you sleep?
Tier 2 · brain / dreams
- 3
Why do you feel sleepier and sleepier the longer you stay awake?
Tier 2 · brain / body clock
- 4
Why does your brain feel like mush when you have not slept enough?
Tier 2-3 · brain / focus
Amazing Animal Senses
BiologyAnimals reach the very same world through completely different doors: sound, smell, the faintest light, even electricity.
- 1
How does a bat swoop through pitch darkness without crashing?
Tier 2 · animals / senses / sound
- 2
Why can a dog smell things that you cannot smell at all?
Tier 1 · animals / senses / smell
- 3
How does a cat see in a room that looks pitch black to you?
Tier 2 · animals / senses / sight
- 4
How does a shark find a fish hiding motionless under the sand?
Tier 3 · animals / senses / electricity
Animal Defence & Camouflage
BiologyStaying alive takes a whole toolkit: hiding, bold warnings, convincing fakery, and occasionally an answer nobody saw coming.
- 1
How does an octopus vanish by turning the colour of the rock it sits on?
Tier 2 · animals / camouflage
- 2
Why would a tiny frog be a bright, bold colour instead of hiding?
Tier 2 · animals / defence
- 3
Why do zebras wear such bold black-and-white stripes out in the open?
Tier 2 · animals / patterns
- 4
Why would an animal flop over and pretend to be dead when attacked?
Tier 2 · animals / survival
Plant Defences
BiologyPlants cannot run away, so they defend themselves with stings, spikes, poisons and fiery chemicals.
- 1
How does a plant that cannot move give you such a nasty sting?
Tier 1 · plants / defences
- 2
Why are so many plants covered in sharp thorns and spikes?
Tier 1 · plants / defences
- 3
Why would a plant make its own fruit burn your mouth?
Tier 2 · plants / seeds
- 4
Why are some pretty berries deadly poison to eat?
Tier 2-3 · plants / poison
Gases & Air
ChemistryAir is real stuff made of countless fast-moving invisible particles, and though you cannot see them, they spread, squeeze and push.
- 1
How does the smell of dinner reach your nose two rooms away?
Tier 1-2 · gases / smell
- 2
Why does a blown-up balloon slowly go soft and shrink after a few days?
Tier 2 · gases / particles
- 3
Why does a bike pump grow warm in your hands as you pump hard?
Tier 2-3 · gases / heat
- 4
Why does a spray can turn cold as you use it?
Tier 3 · gases / cooling
Magnets
PhysicsEvery magnet has two opposite ends with an invisible field between them, it is fussy about which metals it will bother with, and electricity can conjure one up out of nothing.
- 1
Why does every magnet have two ends that behave in opposite ways?
Tier 2 · physics / magnets
- 2
Why do two magnets snap together one way but shove apart the other?
Tier 2 · physics / magnets
- 3
Why does a magnet grab the fridge door but ignore the wall right beside it?
Tier 1 · physics / magnets
- 4
How can you make a magnet that turns on and off at the flick of a switch?
Tier 2-3 · physics / magnets / electricity
Water Pressure & Diving
PhysicsWater pushes on everything in it and pushes harder the deeper you go, and that one rule shapes ears, dams, fountains and the hulls of submarines.
- 1
Why do your ears start to ache when you swim down to the bottom of a deep pool?
Tier 2 · water / pressure / body
- 2
Why is a giant dam wall built far thicker at the bottom than the top?
Tier 2 · water / pressure / forces
- 3
Why does water shoot out further from a hole near the bottom of a bottle than a hole near the top?
Tier 2 · water / pressure / forces
- 4
How does a heavy metal submarine choose to sink, then float back up?
Tier 2-3 · water / pressure / density
Ears & Balance
The Human BodyYour ear does more than listen: the same small space keeps you upright, tells your brain how you are moving, and quietly cleans and defends itself.
- 1
How does your ear turn a wobble in the air into a sound you can hear?
Tier 2 · ears / hearing
- 2
Why does the room keep spinning for a moment after you stop twirling?
Tier 2 · ears / balance
- 3
Why does reading in a moving car make you feel so queasy?
Tier 2-3 · body / balance
- 4
Is earwax just gunk, or is it there for a reason?
Tier 1-2 · ears / body
Feelings in Your Body
The Human BodyFeelings are not just in your head; your body joins in, with a racing heart, hot cheeks or butterflies in your tummy.
- 1
Why do salty tears spill out of your eyes when you feel sad?
Tier 2 · the body / emotions
- 2
Why do your cheeks flush bright red when you feel embarrassed?
Tier 2 · the body / skin
- 3
Why do you feel fluttery butterflies in your tummy before something scary?
Tier 2 · the body / nerves
- 4
Why does a really good laugh leave you feeling wonderful?
Tier 2 · the brain / mood
Teeth
The Human BodyYour teeth are living tools built for the job, and looking after them keeps them working for life.
- 1
Why do your first teeth fall out just when you have got used to them?
Tier 1 · the body / teeth / growing
- 2
Why are your front teeth flat and sharp but your back teeth bumpy?
Tier 1 · the body / teeth / eating
- 3
Why do teeth go bad and get holes if you forget to brush them?
Tier 2 · the body / teeth / germs
- 4
Why is the shiny coat on your teeth the hardest stuff your body makes?
Tier 2-3 · the body / teeth / materials
Weather Extremes
Earth & SpaceThe same heat and moving air that make everyday weather can, in the right conditions, whip up wild and violent storms.
- 1
How does a wild spinning tornado drop down out of a storm cloud?
Tier 3 · weather / storms / air
- 2
How does a hurricane grow into a storm hundreds of miles wide?
Tier 2 · weather / storms / oceans
- 3
How do lumps of solid ice fall from a summer sky?
Tier 2 · weather / storms / ice
- 4
What makes a jagged bolt of lightning suddenly leap across the sky?
Tier 2 · weather / electricity / storms
Time & the Calendar
Earth & SpaceOur days and years are not human inventions at all. They are the spin of the Earth and its journey round the Sun, awkward leftover minutes and all.
- 1
Why is a day exactly one day long, and where does that length come from?
Tier 1 · earth & space / time
- 2
Why does a year last 365 days, and not some other number?
Tier 1-2 · earth & space / time
- 3
Why do we bolt an extra day onto February every four years?
Tier 2 · earth & space / time
- 4
How did people know what time it was before clocks and phones existed?
Tier 2 · earth & space / time
Baby Animals & Life Cycles
BiologyAnimals begin life in wonderfully different ways, from eggs to live young, and grow up through changing stages.
- 1
Why do birds lay eggs instead of carrying their babies inside like we do?
Tier 2 · animals / birds / life cycles
- 2
How does a wriggly water tadpole become a hopping land frog?
Tier 2 · animals / amphibians / growth
- 3
Why do baby mammals drink milk before they can eat anything else?
Tier 1-2 · animals / mammals / babies
- 4
Why is a newborn kangaroo tinier than your thumb, and how does it finish growing in a pouch?
Tier 2-3 · animals / mammals / marsupials
Momentum & Collisions
PhysicsA moving object carries a push called momentum, and when things collide that push is passed on or shared out, never simply lost.
- 1
Why does lifting one ball of a Newton's cradle make the ball at the far end jump?
Tier 1 · momentum collisions physics
- 2
Why does a cannon lurch backwards the moment it fires a ball forwards?
Tier 2 · momentum recoil physics
- 3
Why do two ice skaters both glide backwards when only one gives a push?
Tier 2 · momentum forces physics
- 4
Why does catching a hard ball hurt less if you sweep your hands back as you catch it?
Tier 2-3 · momentum impulse physics
Projectiles & Throwing
PhysicsOnce something is thrown, gravity pulls it downward at a steady rate while it keeps moving forward, and those two together bend its path into a curve.
- 1
Why does a thrown ball always arc downward instead of flying in a straight line?
Tier 1 · physics, motion, forces
- 2
Why do a ball you drop and a ball you throw sideways hit the floor at the same moment?
Tier 2 · physics, motion, gravity
- 3
Why must you aim above a faraway target to actually hit it?
Tier 2-3 · physics, projectiles, aiming
- 4
Why does a jet of water from a hose curve down into a lovely arch?
Tier 1-2 · physics, water, projectiles
Going in Circles
PhysicsTo keep moving in a circle, something must be pulled constantly toward the centre; take away that inward pull and it flies off in a straight line.
- 1
Why do you feel flung outwards when a roundabout spins fast?
Tier 2 · forces circular-motion spinning
- 2
Why does the water stay in when you swing a bucket in a full circle over your head?
Tier 2 · forces circular-motion gravity
- 3
Why does a cyclist tip inwards when turning a fast corner?
Tier 3 · forces friction balance turning
- 4
How does a spinning drum get the water out of your wet clothes?
Tier 2 · forces circular-motion water
Heat on the Move
PhysicsHeat gets around by riding along in moving air and water, and by streaming across empty space as light, and between them those two explain most everyday warm-ups and cool-downs.
- 1
How does one small radiator manage to warm a whole big room?
Tier 1-2 · heat, air, convection
- 2
How does the Sun's warmth reach you across space with almost nothing in between?
Tier 2 · heat, sun, radiation
- 3
Why does the breeze at the seaside blow one way by day and the other by night?
Tier 2-3 · heat, wind, weather
- 4
Why do you roast in a black t-shirt but stay cooler in a white one?
Tier 1 · heat, light, colour
Resonance
PhysicsEverything has a natural rhythm it likes to wobble at, and small pushes repeated at exactly that rhythm can build up into a surprisingly big wobble.
- 1
How can a singer smash a wine glass using nothing but their voice?
Tier 2-3 · sound resonance physics
- 2
Why are marching soldiers ordered to fall out of step when crossing a bridge?
Tier 2-3 · forces resonance bridges
- 3
How does a radio pluck one station out of all the signals in the air at once?
Tier 2-3 · radio waves resonance
- 4
Why does a window buzz and rattle when a heavy lorry rumbles by?
Tier 1-2 · sound vibration resonance
Melting & Boiling
ChemistryMaterials change state at temperatures set by how tightly they hold themselves together, though pressure, hidden energy and even the way something was cooled can all shift the number.
- 1
Why does butter melt in a warm hand but a metal spoon needs a furnace?
Tier 2 · melting / particles / bonds
- 2
Why does a pan of water boil at the same temperature every time in your kitchen?
Tier 2 · boiling / heat / temperature
- 3
Why does a drink full of ice stay icy cold right up until the last cube melts?
Tier 2 · ice / cooling / heat
- 4
Why does chocolate go gooey in your warm hand while a pebble stays solid?
Tier 1 · chocolate / melting / temperature
How Fast Reactions Go
ChemistryHow fast a change happens depends on how often the pieces meet and how hard they hit, so heat, surface area and the supply of an ingredient are the levers you can pull.
- 1
Why do small chopped pieces of food cook so much faster than one big lump?
Tier 1 · chemistry reactions cooking heat
- 2
Why does a cold fridge keep food fresh for days longer than a warm cupboard?
Tier 2 · chemistry reactions food cold
- 3
Why does fanning a fire make it roar up instead of blowing it out?
Tier 2 · chemistry reactions fire oxygen
- 4
Why does a fizzy tablet whoosh away far faster in warm water than cold?
Tier 2 · chemistry reactions dissolving heat
Oil & Plastics
ChemistryWe build plastics out of oil dug from the ground, and the very qualities that make them so useful are what make them so hard for the world to be rid of afterwards.
- 1
How does thick black oil from underground become a clear plastic bottle?
Tier 2 · plastic oil chemistry
- 2
Why does a plastic bottle still sit whole in the ground hundreds of years later?
Tier 2-3 · plastic decay environment
- 3
Why is plastic floating in the ocean so harmful to sea creatures?
Tier 1-2 · plastic ocean pollution
- 4
How does putting a bottle in the recycling bin actually help the planet?
Tier 1 · recycling plastic energy
Traits in Families
BiologyYou inherit a shuffled hand of instructions from your parents, and whether a trait hides, skips a generation or appears from nowhere depends on how many instructions have a say and which parent they came from.
- 1
How can two brown-eyed parents end up with a blue-eyed baby?
Tier 2 · genetics inheritance eyes
- 2
Why can a feature vanish in the parents but pop up again in the grandchildren?
Tier 2 · genetics inheritance recessive
- 3
Why are boys far more likely to be colour-blind than girls?
Tier 3 · genetics chromosomes vision
- 4
Why might you end up with your grandmother's nose, skipping your parents?
Tier 2 · genetics inheritance family
Life's Family Tree
BiologyScientists sort every living thing into groups by the features they share, building a giant family tree that shows how all creatures are related.
- 1
Why do scientists bother sorting millions of living things into neat groups?
Tier 1 · classification family tree
- 2
A bat flies like a bird, so why do scientists call it a mammal?
Tier 2 · mammals bats classification
- 3
A whale looks just like a giant fish, so why is it really closer kin to a hippo?
Tier 2 · whales mammals evolution
- 4
How can scientists tell which animals are close cousins on the family tree?
Tier 3 · dna bones classification
How Tiny Is a Germ?
MicrobesGerms are so unimaginably small that millions can sit on a pinhead, which is why we needed microscopes to uncover the hidden world that shapes our health.
- 1
Why can germs make you ill when you cannot see a single one?
Tier 1 · microbes / size / eyesight
- 2
A bacterium is already tiny, so how much smaller still is a virus?
Tier 2-3 · microbes / viruses / scale
- 3
How many germs could be sitting on your fingertip right now?
Tier 2 · microbes / numbers / skin
- 4
How does a microscope let us see a world too small for our eyes?
Tier 2-3 · microbes / microscopes / light
Antibiotics & Superbugs
MicrobesAntibiotics are medicines that kill harmful bacteria, but bacteria can slowly become able to survive them, which is why we must use these medicines with great care.
- 1
How does an antibiotic wipe out the bacteria making you ill without harming you?
Tier 2 · microbes antibiotics medicine
- 2
What exactly is a superbug, and why do they scare doctors?
Tier 2 · microbes superbugs antibiotics
- 3
Why does the doctor tell you exactly how long to take antibiotics for?
Tier 2 · microbes antibiotics medicine
- 4
Why do doctors hold back on antibiotics instead of giving them for every sniffle?
Tier 2-3 · microbes antibiotics viruses
Life in Extreme Places
MicrobesLife turns up in places that ought to kill it, from boiling springs to solid ice to the lightless deep, and every survivor has its own trick for the impossible.
- 1
How can tiny living things survive in water hot enough to cook an egg?
Tier 2 · microbes extreme heat
- 2
How do some tiny creatures live through being frozen solid in ice?
Tier 2-3 · microbes freezing survival
- 3
How does a tardigrade survive being dried out, frozen, and even blasted into space?
Tier 2 · tardigrade extreme survival
- 4
How does a whole world of life thrive around deep-sea vents in total darkness?
Tier 3 · deep-sea microbes darkness
How Genes Build You
BiologyYour DNA is a recipe book, and your cells read its genes to build tiny machines called proteins that carry out nearly every job in your body.
- 1
How does a coil of DNA end up building a whole living body?
Tier 1 · dna and genes
- 2
What are proteins, and why does almost everything in you depend on them?
Tier 2 · what proteins do
- 3
If every cell holds the very same DNA, why is a skin cell so different from a brain cell?
Tier 2 · cells and dna
- 4
How does one cell in a growing baby know whether to become skin, bone or blood?
Tier 3 · growing cells
Editing Life
BiologyScientists can now read and even rewrite the instructions inside living things, which brings amazing powers along with big questions about how we should use them.
- 1
What does it mean when food is called genetically modified?
Tier 2 · genetics / food
- 2
How can scientists actually rewrite the instructions inside a living thing?
Tier 3 · genetics / dna
- 3
What is cloning, and how can two living things be exactly the same?
Tier 2-3 · genetics / cloning
- 4
We can now change the code of life, but does that always mean we should?
Tier 3 · genetics / ethics
How New Species Arise
BiologyWhen groups of the same animal are kept apart for long enough, they change in different ways until they become entirely separate species.
- 1
How does a single kind of animal split into two completely different species?
Tier 3 · how new species form
- 2
Why are the strangest, most unique animals often found on faraway islands?
Tier 2 · island evolution
- 3
Why do the same little finches have such different beaks from one island to the next?
Tier 2 · beaks and evolution
- 4
How do scientists decide that two similar animals are really separate species?
Tier 3 · what a species is
How Plants Live on Land
BiologyPlants had to solve big problems to survive on dry land, from drawing water through roots to standing tall without water to hold them up.
- 1
How did the very first plants manage to leave the water and live on dry land?
Tier 2 · plants / biology
- 2
Beyond somewhere to stand, why do most plants really need soil?
Tier 2 · plants / biology
- 3
Why do some plants trap and eat insects instead of just soaking up sunlight?
Tier 2 · plants / biology
- 4
Why is nearly every plant built from the same three parts: roots, stem and leaves?
Tier 3 · plants / biology
Boom & Crash
BiologyIn the wild, the numbers of hunters and their prey rise and fall together in a never-ending, self-correcting cycle.
- 1
Why do the numbers of foxes and rabbits chase each other up and down over the years?
Tier 2 · predators and prey
- 2
Why cannot a single kind of animal simply keep breeding until it covers the whole land?
Tier 2 · animal populations
- 3
What goes wrong when all the hunters are taken out of a habitat?
Tier 2 · food chains
- 4
With no one in charge, how does the wild keep itself roughly in balance?
Tier 3 · nature in balance
Why Animals Behave
BiologyMuch of what animals do, travelling enormous distances, sleeping through winter, crowding together, signalling to each other, is behaviour shaped to keep them alive and understood.
- 1
Why do some birds fly halfway around the world and back every year?
Tier 2 · migration / survival / food
- 2
Why do some animals sleep right through the whole winter?
Tier 2 · hibernation / winter / energy
- 3
Why do so many animals choose to live crowded together in big groups?
Tier 2 · animal groups / safety
- 4
Why does a dog wag its tail, and what is it trying to tell you?
Tier 1 · animal behaviour / communication
Reading Starlight
Earth & SpaceA star is far too distant to visit, so everything we know about it has to be squeezed out of its light, and out of the instruments patient enough to gather that light.
- 1
How can we possibly know what a star is made of without ever going there?
Tier 3 · starlight and colour
- 2
How do astronomers measure how far away a star is when it is impossibly far?
Tier 2 · measuring the stars
- 3
How can we tell whether a distant star is racing toward us or away?
Tier 2 · moving stars
- 4
How does a telescope reveal faint stars your eyes could never spot?
Tier 1 · telescopes and light
Are We Alone?
Earth & SpaceAstronomers hunt for planets circling other stars and ask whether any could hold life, using careful science rather than guesswork.
- 1
How do we spot planets around distant stars when the stars themselves are mere dots?
Tier 2 · hunting for planets
- 2
What would a faraway planet need to have a real chance of life?
Tier 2 · worlds for life
- 3
Why is finding water the first thing scientists look for when searching for life?
Tier 1 · water and life
- 4
If aliens existed, how could we possibly hear them across space?
Tier 2 · listening for aliens
Your Amazing Brain
The Human BodyYour brain is a living network of billions of tiny cells that store memories, learn new skills and let you think, all using tiny bursts of electricity.
- 1
Where in your head does a memory actually get stored?
Tier 2 · brain and memory
- 2
Why does your brain let some memories slip away completely?
Tier 2 · memory and forgetting
- 3
Why does practising the same thing over and over slowly make you brilliant at it?
Tier 2 · brain and learning
- 4
How quickly do thoughts and signals zip around inside your brain?
Tier 2 · brain signals
Allergies
The Human BodyAn allergy is your body's defence system overreacting to something harmless, treating a peanut or a speck of pollen as if it were a dangerous invader.
- 1
What is really going on inside you when you have an allergic reaction?
Tier 1 · allergies and immunity
- 2
Why does a tiny grain of pollen set off sneezing and itchy, streaming eyes?
Tier 1 · allergies and the nose
- 3
Why can one person eat peanuts happily while they make another person dangerously ill?
Tier 2 · allergies and immunity
- 4
Why do some children have an allergy when young, then lose it as they grow?
Tier 2 · allergies and immunity
Are Viruses Alive?
MicrobesA virus can do nothing whatsoever on its own, yet it hijacks your cells to multiply, and that strange half-alive nature is exactly why it is so hard to catch out, treat or be rid of.
- 1
Is a virus a living creature, or something stranger in between?
Tier 2 · microbes / living things
- 2
A virus cannot even move on its own, so how does it manage to make you ill?
Tier 2 · microbes / your body
- 3
Why can you catch cold after cold, even after having one just last month?
Tier 2 · microbes / immune system
- 4
Why, with all our science, is there still no pill that cures the common cold?
Tier 3 · microbes / medicine
How Outbreaks Spread
MicrobesOne sick person can start a chain that reaches thousands, which is why understanding how germs travel helps us stop them.
- 1
How exactly does a germ get from a sick person into a healthy one?
Tier 1 · how germs travel
- 2
Why does illness race through a packed school or busy city so quickly?
Tier 2 · crowds and spread
- 3
How can a single sick person end up causing thousands of others to fall ill?
Tier 3 · outbreak chains
- 4
When an illness starts to spread, how do we actually stop it in its tracks?
Tier 2 · stopping an outbreak
Microbes at Work
MicrobesMicrobes are hard workers we quietly depend on: they make our food, clean our water, brew our medicines and clear away everything that dies.
- 1
How do invisible microbes turn plain milk into hundreds of kinds of cheese?
Tier 1 · microbes and cheese
- 2
How do microbes help clean the dirty water that leaves our homes?
Tier 2 · microbes clean water
- 3
How can tiny microbes be put to work brewing life-saving medicines?
Tier 3 · microbe medicine makers
- 4
When a plant or animal dies, how do microbes tidy it all away?
Tier 2 · microbe recyclers
The Speed of Light & Relativity
PhysicsLight has a top speed that nothing can ever beat, and chasing that one idea leads somewhere astonishing: space and time themselves stretch and bend.
- 1
Why is there a top speed in the universe that nothing can ever beat?
Tier 3 · light speed limit
- 2
Why would a clock on a super-fast spaceship tick slower than one back home?
Tier 3 · time and motion
- 3
How could a twin who flies to the stars return younger than the twin who stayed home?
Tier 3 · relativity and time
- 4
Why does light rush past you at the same speed whether you chase it or flee from it?
Tier 3 · the speed of light
The Quantum World
PhysicsZoom in far below atoms and the everyday rules break down: the tiniest bits of the universe act as both waves and particles, and behave in ways that seem impossible.
- 1
Is light a spread-out wave, or a stream of tiny separate bits?
Tier 3 · quantum light
- 2
Why can the electrons in an atom only hold certain fixed amounts of energy, never the amounts in between?
Tier 3 · atoms and energy
- 3
If you kept zooming in past the atom, what would you finally find?
Tier 3 · particle physics
- 4
Why do even brilliant scientists say the quantum world is downright weird?
Tier 3 · quantum weirdness
Radioactivity & Nuclear Power
PhysicsDeep inside every atom sits a tiny core packed with enormous energy, and learning to unlock it gave us both radioactivity and nuclear power.
- 1
What is radioactivity, the invisible thing that ticks on a Geiger counter?
Tier 3 · invisible atomic energy
- 2
Why are some atoms perfectly steady while others slowly fall apart?
Tier 3 · wobbly atomic cores
- 3
How does splitting tiny atoms end up lighting a whole city?
Tier 3 · splitting atoms for power
- 4
Could we build a tiny star on Earth to power the whole world cleanly?
Tier 3 · a star on earth
Bridges & Buildings
PhysicsBuilders beat gravity with clever shapes and clever balance, so that arches, towers and cranes can carry loads far heavier than themselves.
- 1
Why can a curved stone arch hold up a heavy bridge without any glue?
Tier 2 · forces and shapes
- 2
Why are cranes, bridges and towers packed full of triangle shapes?
Tier 1 · shapes and structures
- 3
Why is it safer for a skyscraper to sway in the wind than to stand rock-solid?
Tier 2 · forces and materials
- 4
How does a towering crane lift enormous weights without tipping straight over?
Tier 3 · balance and forces
How Everyday Gadgets Work
PhysicsThe everyday machines around you run on hidden science: moving heat about, bouncing invisible waves, and reading tiny electric signals.
- 1
How does a fridge make the inside cold when there is no ice or snow in it?
Tier 2-3 · heat / energy
- 2
How does a microwave heat your dinner without getting hot itself?
Tier 2 · waves / heat
- 3
How does a glass touchscreen know exactly where your finger taps?
Tier 2-3 · electricity
- 4
How does a speaker turn a stream of electricity into music you can hear?
Tier 2-3 · electricity / sound
Rivers & Erosion
Earth & SpaceWater is a patient sculptor: given enough time, rivers and rain carve deep valleys, cut caves, and grind solid rock down into sand.
- 1
How does a gentle river slice a deep valley through solid rock?
Tier 1 · rivers and erosion
- 2
Why does a waterfall very slowly creep upstream, year after year?
Tier 2 · waterfalls and erosion
- 3
How do huge caves hollow out deep inside solid rock underground?
Tier 2 · caves and rock
- 4
Where do all the countless grains of sand on a beach actually come from?
Tier 1 · beaches and erosion
Rocks & the Rock Cycle
Earth & SpaceRocks are not forever: heat, pressure and weather remake them endlessly, and how a rock was made decides whether you can build with it or crumble it in your hand.
- 1
Rocks seem like they have always just been there, so how are new ones made?
Tier 2 · how rocks form
- 2
Why are pebbles in a river so smooth and round when mountain rocks are jagged?
Tier 1 · rivers and erosion
- 3
How can a soft, crumbly rock slowly turn into hard, sparkling stone?
Tier 2 · rocks under pressure
- 4
Why is one rock tough enough to build with while another crumbles to dust?
Tier 2 · what makes rock strong
The Oceans
Earth & SpaceThe ocean is a vast, restless, salty world with slow rivers running through it, a black and freezing floor, and crowds of life packed into the few places that suit.
- 1
Why is the sea so salty when the rivers and rain that fill it are not?
Tier 1 · oceans and salt
- 2
Why does the ocean flow in enormous rivers-within-the-sea called currents?
Tier 3 · ocean currents
- 3
Why is the bottom of the deep ocean pitch black and freezing cold?
Tier 2 · the deep sea
- 4
Why does a coral reef bustle with more creatures than almost anywhere in the sea?
Tier 2 · coral reefs
Trees & Forests
BiologyA tree keeps a record of its own life and has its own plan for winter, and gathered into a forest, trees become both a habitat and a set of lungs the whole planet leans on.
- 1
How can the rings inside a cut tree tell you exactly how old it was?
Tier 1 · trees / growth
- 2
Why do pine trees stay green all winter while oak trees go bare?
Tier 2 · trees / winter
- 3
Why does a single forest shelter such an enormous number of different creatures?
Tier 2 · forests / biodiversity
- 4
Why do people call forests the lungs of the planet, worth protecting everywhere?
Tier 3 · forests / climate
The Science of Music
PhysicsMusic is science you can hear: the size, shape and material of an instrument decide the notes it plays and the special voice it sings with.
- 1
Why does the very same note sound so different on a piano and a violin?
Tier 3 · sound and music
- 2
Why does a huge double bass rumble low while a tiny violin sings high?
Tier 2 · sound and pitch
- 3
How does whacking a stretched drum skin fill the room with a boom?
Tier 2 · sound and vibration
- 4
How does blowing across the top of an empty bottle make a note?
Tier 2 · sound and air
Reading the Night Sky
Earth & SpacePeople have read patterns and guides into the night sky for thousands of years, and simple stargazing still shows how the sky turns, what wanders across it, and where your own eyes deceive you.
- 1
Why do the stars seem to join up into pictures like a hunter or a bear?
Tier 2 · stars and sky
- 2
Why does one star stay put all night while the rest slowly circle around it?
Tier 2 · stars and sky
- 3
Why does the Moon look enormous near the horizon but small high in the sky?
Tier 1 · moon and sky
- 4
Why do a few bright dots slowly drift against the fixed pattern of stars?
Tier 2 · planets and sky
Exercise & Your Body
The Human BodyHard exercise sets your whole body scrambling, and what follows, the stitches, the aches and the slow gain in strength, is the body answering back.
- 1
Why do athletes always warm up first instead of just going flat out?
Tier 1 · exercise and muscles
- 2
Why do you sometimes get that sharp stabbing stitch in your side when running?
Tier 2 · breathing and exercise
- 3
Why does doing sport again and again slowly make you fitter and stronger?
Tier 2 · fitness and training
- 4
Why are your muscles most sore the day AFTER a tough workout, not during it?
Tier 3 · muscles and recovery
Animal Teamwork
BiologyAll across nature, wildly different living things strike deals with one another, and these partnerships hold together only for as long as both sides come out ahead.
- 1
Why does a little clownfish make its home inside a deadly stinging anemone?
Tier 1 · ocean life
- 2
Why do small birds happily perch and peck all over a giant buffalo or rhino?
Tier 1 · grassland animals
- 3
Why does a big fish let a tiny cleaner fish swim right inside its mouth unharmed?
Tier 2 · coral reef life
- 4
How do threads of hidden fungi team up with plant roots deep underground?
Tier 3 · plants and fungi
Metals & Alloys
ChemistryMetals share a hidden arrangement of their atoms that makes them shiny and able to carry electricity, and beyond that each has its own character: how it corrodes, what it will mix with, whether a magnet cares about it at all.
- 1
Why are nearly all metals shiny, and why can they carry electricity so well?
Tier 2 · metals and electricity
- 2
Why do we so often mix metals together instead of using them pure?
Tier 2 · mixing metals
- 3
Why do gold and silver keep their shine for centuries while iron crumbles into rust?
Tier 1 · rust and reactivity
- 4
Why does a magnet grab iron and steel but ignore copper, gold and aluminium?
Tier 3 · magnetic metals
Animal Colours & Glow
BiologyAnimals get their dazzling colours, and even their own glow, in surprising ways: from the food they eat, from chemistry inside them, and from tricks of light on their skin.
- 1
Why are flamingos a beautiful pink when their chicks hatch out grey?
Tier 1 · animal colours
- 2
How does a firefly switch on its own little lantern on a summer night?
Tier 2 · bioluminescence
- 3
Why do so many creatures in the pitch-black deep sea make their own light?
Tier 2 · deep sea life
- 4
Why do some butterfly wings flash and shift colour as they tilt in the light?
Tier 3 · structural colour
Lasers & Light Tech
PhysicsA laser is a very special, tidy kind of light, and learning to tame light like this now powers barcode scanners, the internet and much more.
- 1
How is a laser beam so different from the light of an ordinary torch?
Tier 2 · laser light
- 2
How does the little red beam at a shop till read those black-and-white stripes?
Tier 2 · barcodes and light
- 3
How can the whole internet zoom down a hair-thin thread of glass as flashes of light?
Tier 3 · fibre optics
- 4
How does a flat shiny sticker hold a picture that looks solid and 3D?
Tier 3 · holograms and light
Taste & Smell
The Human BodyTaste and smell team up to give food its flavour, using tiny detectors that also keep you safe and stir up powerful memories.
- 1
Why does your favourite food taste of almost nothing when your nose is blocked?
Tier 1 · taste and smell
- 2
Why can one whiff of a smell suddenly throw you back to a moment years ago?
Tier 2 · smell and memory
- 3
Why are we born loving sweet tastes but screwing up our faces at bitter ones?
Tier 2 · taste and survival
- 4
Why does the herb coriander taste fresh to some people but like soap to others?
Tier 3 · taste and genes
Amazing Animal Powers
BiologyAnimals have evolved astonishing real-life superpowers, from regrowing lost body parts to holding their breath for the best part of an hour.
- 1
How can a lizard drop its tail to escape, then simply grow a brand new one?
Tier 2 · regrowing body parts
- 2
How can a seal or a whale stay underwater for the best part of an hour on one breath?
Tier 2 · holding your breath
- 3
How can a tiny ant carry a crumb many times heavier than its whole body?
Tier 3 · strength and size
- 4
How does a cheetah reach the speed of a car in just a few strides?
Tier 1 · built for speed
Living in Space
Earth & SpaceOn a space station nothing ever feels heavy, so the simplest daily things have to be rethought, and a body that is never asked to hold itself up quietly begins taking itself apart.
- 1
How do astronauts eat a meal and sip a drink when everything just floats away?
Tier 1 · eating in space
- 2
Why do astronauts come back from space with weaker bones and muscles?
Tier 2 · the body in space
- 3
How does an astronaut go to sleep when there is no bed to lie down on?
Tier 1 · sleeping in space
- 4
Why do astronauts have to spend hours exercising every single day in space?
Tier 2 · keeping fit in space
The Air We Breathe
ChemistryThe air is a real mixture of gases, and following the oxygen through it, into fires, into bodies and back out again, explains a great deal, including what makes air dirty.
- 1
What is the air really made of, beyond just the oxygen we breathe?
Tier 1 · gases in air
- 2
Why do a crackling fire and a running child both need the very same oxygen?
Tier 2 · burning and breathing
- 3
Why is the air you puff out not the same as the fresh air you breathed in?
Tier 2 · breathing out
- 4
What actually is air pollution, and why does breathing clean air matter so much?
Tier 2 · air pollution
Forecasting the Weather
Earth & SpaceForecasting means reading the signs the sky, the air and the sea give off, some of them with a glance upward and some with the biggest computers on Earth.
- 1
How can anyone possibly know what the weather will do tomorrow?
Tier 2 · weather / forecasting
- 2
How can the clouds in the sky give you a clue about the weather to come?
Tier 2 · weather / clouds
- 3
How does an old-fashioned barometer hint that a storm is on its way?
Tier 2 · weather / air pressure
- 4
Why does living near the sea change the weather you get?
Tier 2 · weather / oceans
500 mysteries across 125 topics, and the collection keeps growing.