Water

A dirty snowball

What Is a Comet?

Comets are icy leftovers that steam into a bright tail near the Sun.

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Pressure from below

Why Does Water Push Up?

Buoyancy exists because water pressure is greater at the bottom of an object than the top.

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Climbing without a pump

Why Does Water Climb Up a Paper Towel?

Water climbs a paper towel because it grips the fibres more strongly than gravity can pull it back down.

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Heavy for its size

What Is Density?

Density is how much mass is squeezed into a given amount of space.

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Water pushes back

Why Do Things Float?

Things float when the water they push aside weighs more than they do.

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Water breaks the rules

Why Does Ice Float?

Ice floats because freezing forces water molecules into a roomier pattern.

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Light changing lanes

Why Does a Straw Look Bent?

A straw looks broken because light bends when it leaves water and enters air.

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A thin film of water

Why Is Ice So Slippery?

Ice is slippery because its surface always carries a thin film of liquid water to slide on.

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Nothing is pushing it out

Why Does the Water Stay in the Bucket?

Swung water stays in because it keeps moving straight while the bucket curves into its path.

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A skin made of pulling

Why Does a Paperclip Float on Water?

A paperclip floats because water molecules cling to each other, giving the surface a skin that resists being broken.

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A cliff of tiny shells

What Is Chalk Made Of?

Chalk is soft white rock made from the shells of countless tiny sea creatures that settled on an ancient sea floor.

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Flat plates with water between them

Why Can You Shape Clay but Not Sand?

Clay can be shaped because its grains are flat plates that slide on water and stay wherever you leave them.

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It sets by reacting, not by drying

Why Does Concrete Go Hard Under Water?

Concrete hardens by reacting with water rather than losing it, which is why it can set at the bottom of a river.

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Mostly air, in tiny boxes

Why Does Cork Float?

Cork is tree bark full of sealed air-filled cells, which makes it float, squash, and keep bottles shut.

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Some colour dissolves, some just sits there

Why Does Ink Stay on the Paper?

Ink is colour carried in a liquid that then leaves, either soaking into the fibres or drying on top of them.

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Stopping something from rotting

How Does Skin Become Leather?

Leather is animal skin treated so its fibres cannot rot, staying flexible and tough for years.

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Fibres, shaken flat and let dry

How Is Paper Made From a Tree?

Paper is a mat of wood fibres, floated in water, drained flat and pressed until they grip each other.

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Mixed together, not joined together

Why Can You Get the Salt Back Out?

A mixture is stuff jumbled together but not joined, which is why you can always get the pieces back out.

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Two things make a third thing

What Happens When Atoms Join Up?

Atoms join into molecules, and the new thing behaves nothing like the pieces it was made from.

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A rock you are allowed to eat

Where Does Salt Come From?

Salt is a mineral that comes from evaporated seawater or from underground beds left by ancient seas.

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The same temperature, treated gently

Why Do Cooks Simmer Instead of Boil?

Boiling and simmering are the same temperature; boiling only adds violence.

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Fat, turned inside out

How Is Soap Made?

Soap is made by reacting fat or oil with a strong alkali, producing molecules with a water end and a grease end.

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Cooking without soaking

Why Does Steaming Keep the Flavour In?

Steam cooks food at boiling temperature without dissolving its flavour away into water.

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Turning tough into silky

Why Do Cooks Boil Bones for Hours?

Hours of gentle heat turn tough collagen into gelatine, giving stock its body.

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A scale built around water

Why Does Water Freeze at Zero?

Water freezes at zero because the Celsius scale was deliberately built around water's two fixed points.

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A weak layer buried inside

Why Does a Snowy Slope Suddenly Let Go?

Avalanches happen because snow builds in layers, and a weak buried layer can collapse and release the slab above.

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Ice you cannot see

Why Is Black Ice So Dangerous?

Black ice is a clear film of frozen water that looks like wet road and removes almost all grip.

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Water dissolving stone

How Do Caves Form?

Caves form when faintly acidic water slowly dissolves limestone away.

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Reading the sky

Why Do Clouds Have Different Shapes?

Puffy, flat or wispy — a cloud's shape shows how the air under it is moving.

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Droplets too small to fall

How Does Something That Heavy Float?

Clouds float because they are made of droplets so small that air resistance nearly cancels their fall.

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Where the rain never arrives

Why Are Deserts Dry?

Deserts are dry because sinking air, mountains or distance keep the rain away.

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The temperature where air gives up

What Is the Dew Point?

The dew point is the temperature at which air can no longer hold its water as vapour.

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How hard the air pushed

Why Is Some Rain Gentle and Some Rain Heavy?

Heavy rain comes from tall clouds where rising air held drops up until they were huge.

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Rain going missing

What Is a Drought?

A drought is a long stretch of much less water than a place normally depends on.

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Patience with sandpaper

How Do Rivers Carve Canyons?

Rivers cut canyons by dragging sand and stones that grind the rock away.

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Escaping one at a time

Where Does a Puddle Go?

Puddles vanish because fast-moving surface molecules escape into the air as vapour.

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When the ground stops drinking

Why Do Rivers Flood?

Floods happen when rain arrives faster than the soil can soak it up.

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A cloud on the ground

What Is Fog?

Fog is simply a cloud that has formed at ground level.

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Air letting go of water

Why Is the Grass Wet in the Morning?

Dew and frost form because cold surfaces make the air beside them give up water it can no longer carry.

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A kettle with a narrow neck

Why Does the Ground Shoot Boiling Water?

A geyser erupts because pressure holds superheated water back until a small boil triggers a chain reaction.

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Ice that flows

How Do Glaciers Move?

Glaciers are ice piled so deep that it deforms and flows slowly downhill.

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Soaked rock, not caverns

Where Is Water Underground?

Groundwater sits in the tiny spaces between grains of rock, not in hidden lakes.

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Ice going round again

How Does Hail Form?

Hailstones grow by cycling up and down inside a storm, adding a layer each trip.

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When sweat stops working

Why Do Some Hot Days Feel Worse Than Others?

Humid air is already full of water, so your sweat cannot evaporate and cool you.

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A heat engine over warm water

How Do Hurricanes Form?

Hurricanes are giant spinning storms powered by heat released from warm ocean water.

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One-ninth showing

Why Do Icebergs Float So Low?

Ice is only slightly lighter than water, so about nine-tenths of an iceberg is submerged.

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Four different ways

How Does a New Island Appear?

Islands appear in four main ways: volcanic building, coral growth, being cut off, or falling sea level.

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A sea breeze the size of a continent

What Is a Monsoon?

A monsoon is a continent-sized sea breeze that reverses with the seasons.

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Salt arrives and never leaves

Why Is the Sea Salty?

The sea is salty because rivers deliver salt and only fresh water evaporates out.

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Warm and windy beats damp and still

Why Do Puddles Dry Slower Some Days?

Puddles dry fastest in warm, windy air and barely at all in damp air, because molecules land back in as fast as they leave.

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The sky letting go

Where Does Rain Come From?

Rain falls when tiny cloud droplets merge until they are too heavy to float.

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The air arrives empty

Why Is One Side of a Mountain Dry?

Air dumps its rain climbing a mountain, so the far side gets dry wind and no water.

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Raindrops as prisms

How Does a Rainbow Work?

Raindrops bend and reflect sunlight, splitting it into a curved band of colour.

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Erosion on the outside

Why Do Rivers Bend?

Rivers bend because water cuts the outer bank and deposits on the inner one.

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Mountains, eventually

Where Does a Beach Come From?

Sand is what remains after rock is broken down and everything softer has washed away.

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Water eats red light

Why Is the Sea Blue?

The sea looks blue because water absorbs red light quickly and only blue makes it back to your eyes.

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A flake's journey down

Why Does It Sometimes Rain and Snow at Once?

Sleet falls when a snowflake half-melts on the way down and never gets to finish.

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Ice with air in it

Why Is Snow White and Fluffy?

Snowflakes are ice crystals, and snow looks white because of countless surfaces bouncing light.

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Six arms, one journey

Why Is Every Snowflake Different?

Ice always grows six ways, but each flake's journey through the cloud is unique.

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Light not getting through

Why Do Storm Clouds Look Dark?

Storm clouds look dark because they are thick enough to stop light reaching you.

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Wind piling up water

Why Does the Sea Rise in a Storm?

Low pressure lifts the sea slightly and strong wind piles it against the coast.

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The Moon pulling

Why Does the Sea Go In and Out?

Tides happen because the Moon pulls the ocean into bulges that Earth spins through.

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A wave that is all the way down

Why Are Tsunamis So Dangerous?

A tsunami is dangerous because it moves the whole ocean depth, not just the top.

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A loop with no end

Where Does Water Go?

Water evaporates, forms clouds, rains down and flows back to the sea, forever.

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Energy moving, water staying

Do Waves Carry Water Along?

Ocean waves carry energy across the water while the water itself circles in place.

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A windscreen wiper you never think about

Why Do You Blink?

Blinking spreads a fresh layer of tears across your eye, and your brain edits out the moment of darkness.

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Four things in a river

What Is Blood Made Of?

Blood is mostly water, carrying red cells, white cells and platelets around the body.

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Fluid that keeps going

Why Does Spinning Make You Dizzy?

Dizziness happens because the fluid in your ear keeps swirling after you stop, so your ears insist you are still turning.

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Throw it all out, take back what you need

What Do Kidneys Actually Do?

Kidneys clean blood by throwing nearly everything out and carefully taking back the water and salt you need.

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Anchor and straw

What Do Roots Do?

Roots anchor a plant, absorb water and minerals, and trade with soil fungi.

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Cooling by evaporation

Why Do We Sweat?

Sweating cools you because evaporating water takes heat from your skin.

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Three kinds of tear

Why Do We Cry?

There are three kinds of tears: constant maintenance, emergency rinsing, and emotional ones.

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A saltiness detector

How Does Your Body Know You Need a Drink?

Thirst comes from a patch of brain measuring how salty your blood is, not from a dry mouth.

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Some of it — and the sea makes more

Do Trees Make the Air We Breathe?

Trees make oxygen, but tiny ocean plankton produce about half of it.

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A bag that reports on itself

Why Can't You Just Hold It Forever?

Your bladder measures stretch, not volume — which is why the urge comes in waves and why cold makes it worse.

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Both, in a way

Is Coral a Rock or an Animal?

Coral is a colony of tiny animals living inside a stone skeleton they build.

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Legs that bend the wrong way

Why Does a Crab Walk Sideways?

A crab walks sideways because its leg joints only hinge side to side — going sideways is the fast way, not the odd way.

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A pond in a box

Why Do Animals Lay Eggs?

An egg carries water, food and air for a growing animal inside a shell strong enough to sit on and thin enough to breathe through.

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Taking oxygen out of water

How Do Fish Breathe Underwater?

Fish use gills to pull dissolved oxygen out of the water flowing past.

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Two lives, one animal

Why Do Frogs Start as Tadpoles?

Frogs start as water-adapted tadpoles and rebuild into land-adapted adults.

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No brain, no heart, no bones

How Does a Jellyfish Live With No Brain?

A jellyfish has no brain, heart, bones or blood — a ring of nerves and a bag of water do the whole job.

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It is not the bite, it is you

Why Does a Mosquito Bite Itch?

A mosquito's spit stops your blood clotting so it can drink — and your reaction to that spit is the itch.

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Skin that works like a screen

How Does an Octopus Change Colour?

An octopus changes colour with millions of tiny colour bags in its skin, squeezed open and shut by muscle.

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Four layers and a good idea

How Do Penguins Stay Warm in the Snow?

Penguins beat the cold with packed feathers, a fat layer, a clever blood trick in the feet, and taking turns in a huddle.

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Senses you do not have

How Does a Shark Find Its Food?

Sharks hunt with a stack of senses — smell, ripples, and electricity — that reach far past what eyes can do.

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An animal built the wrong way round

How Does a Starfish Grow a New Arm?

A starfish walks on hundreds of tiny water-powered feet, has no brain or blood, and can regrow a lost arm.

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The biggest animal there has ever been

Why Is a Whale Not a Fish?

Whales are warm air-breathers that feed their babies milk, which makes them nothing like the fish they swim beside.

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Water turning to gas inside itself

What Are the Bubbles When Water Boils?

Boiling bubbles are water vapour forming inside the liquid, not trapped air.

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A grain that drinks

Why Does Rice Need Exactly the Right Water?

Rice grains swell by absorbing a set amount of water, so the measure matters more than the time.

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Broken up, not vanished

Where Does Sugar Go in Water?

Dissolving breaks a solid into single molecules spread evenly through the liquid.

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Ice leaving without melting

What Is Freezer Burn?

Freezer burn is ice escaping food as vapour without ever melting, leaving it dry.

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Locking into a pattern

What Happens When Water Freezes?

Freezing locks water molecules into an open pattern that takes up more space.

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Heat always moving in

Why Does Ice Cream Melt?

Ice cream melts because heat always flows from the warmer room into it.

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Lowering the freezing point

Why Does Salt Melt Ice?

Salt lowers water's freezing point, so ice melts at temperatures below zero.

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A liquid that panics

Why Can You Run on Cornflour and Water?

Cornflour mixed with water jams solid when hit and flows when pressed slowly.

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Cloudy water is useful water

Why Do Cooks Save the Pasta Water?

Pasta water carries starch, which thickens a sauce and helps it stick to the pasta.

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Steam bursting out

Why Does Popcorn Pop?

Popcorn pops when trapped water turns to steam and bursts the hard shell.

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Stopping the heat walking out

Why Does a Lid Make Water Boil Faster?

A lid stops steam carrying heat away, so the pan reaches boiling much faster.

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Air losing its grip on water

Why Do Windows Fog Up?

Windows fog when warm moist air touches cold glass and its water condenses.

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Iron combining with oxygen

Why Does Metal Go Rusty?

Rust forms when iron reacts with oxygen and water to make a flaky new substance.

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A molecule with two ends

How Does Soap Clean?

Soap works because each molecule grips grease at one end and water at the other.

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Light bouncing off two surfaces

Why Are Soap Bubbles Colourful?

Bubble colours come from light reflecting off both surfaces of the film and interfering.

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How tightly the molecules hold

Why Are Some Things Solid and Others Runny?

Solids, liquids and gases differ in how tightly their molecules hold together.

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Air pressure pushing from outside

How Does a Straw Work?

A straw works because removing air lets outside air pressure push the drink up.

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Rain, stored on a hillside

How Does a Dam Make Electricity?

A dam holds water high up; letting it fall through a turbine turns the height it lost into electricity.

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Twisting water molecules

Why Does a Microwave Heat Food, Not the Plate?

A microwave heats water by flipping a radio field billions of times a second, so wet food heats and dry plates do not.

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It falls there, mostly

How Does Water Climb to the Tap?

Water reaches your tap because it is stored higher than your house, and height is what makes pressure.

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A siphon, not a plug

Why Does a Toilet Flush by Itself?

A toilet flushes because a sudden rush of water fills the bend behind the bowl, and a full bend pulls the rest away by itself.

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Water carrying straight on

Why Does Spinning Get Clothes Dry?

A spin cycle works because water keeps travelling straight while the drum forces the clothes to turn.

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Pushed from below, never pulled

How Does Water Get Up to the Top Floor?

Water reaches an upstairs tap because a pump pushes it from below — sucking it up stops working after about ten metres.

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