Topic
Heat & cold
Hot, cold, and how warmth moves about — 84 tiny stories from every shelf.
Not a star at all
What Is a Shooting Star?
Shooting stars are specks of dust burning up as they slam into our air.
Let’s go →Both, and neither
Is Space Hot or Freezing?
Space is not really hot or cold, because temperature needs particles and space has almost none.
Let’s go →Not burning at all
What Is the Sun Burning?
The Sun is not burning: crushing pressure fuses hydrogen into helium and releases enormous energy.
Let’s go →A blanket that will not lift
Why Is Venus Hotter Than Mercury?
Venus beats Mercury for heat because its thick atmosphere traps warmth that Mercury simply radiates away.
Let’s go →Jostling passed along
Why Does a Metal Spoon Get Hot?
A metal spoon heats up because vibrating atoms pass their jostling along, and metals pass it exceptionally well.
Let’s go →It never goes anywhere
Where Does Energy Go When Things Stop?
Energy never disappears when something stops; it has simply turned into heat, sound or something else.
Let’s go →Why things stop
What Is Friction?
Friction is the grip between two surfaces that turns motion into heat.
Let’s go →Everything is shaking
What Is Heat?
Heat is the movement of atoms — the faster they jiggle, the hotter it is.
Let’s go →Water breaks the rules
Why Does Ice Float?
Ice floats because freezing forces water molecules into a roomier pattern.
Let’s go →It makes nothing — it slows
Does a Coat Make You Warm?
A coat does not warm you. It traps air and slows the escape of the heat your body already produces.
Let’s go →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.
Let’s go →The part that would not burn
What Is Left When Something Burns?
Ash is the mineral part of the fuel — the bit that could not burn, left sitting there when everything else left as gas.
Let’s go →Fire welds the grains together
Why Does Baking Mud Make Stone?
A brick is mud baked so hot that its grains fuse at the edges and become, in effect, a new stone.
Let’s go →Where roast smells come from
Why Does Food Turn Brown When It Cooks?
Above about 140 °C, sugars and proteins react to make brown colour and roasted flavour.
Let’s go →Burning wood twice
Why Does Charcoal Burn Hotter Than Wood?
Charcoal is wood heated without air until only carbon is left, which then burns hotter and almost smokelessly.
Let’s go →A narrow window of heat
Why Does Custard Suddenly Scramble?
Egg proteins unfold and thicken custard, but a little more heat makes them clump.
Let’s go →Mostly air, held in a shape
Why Is Foam So Light?
Foam is mostly trapped air, which is why it is so light and such a good insulator.
Let’s go →Oil goes far hotter than water
Why Does Frying Taste Different From Boiling?
Oil reaches far higher temperatures than water, so frying browns food that boiling only softens.
Let’s go →A mesh built from fruit
Why Does Jam Set?
Jam sets when pectin from fruit forms a mesh that traps the sugary liquid.
Let’s go →Melted, then cooled too fast to crystallise
How Do You Turn Sand Into a Window?
Glass is melted sand, cooled so fast that the atoms freeze in place before they can form crystals.
Let’s go →How hard the atoms hold on
Why Do You Need a Furnace to Melt Iron?
Metals melt at wildly different temperatures because their atoms grip each other with wildly different strength.
Let’s go →The same temperature, treated gently
Why Do Cooks Simmer Instead of Boil?
Boiling and simmering are the same temperature; boiling only adds violence.
Let’s go →The bits that did not get to burn
Why Does a Fire Make Smoke?
Smoke is fuel that never finished burning — tiny solid specks, lifted away by the rising hot air.
Let’s go →Cooking without soaking
Why Does Steaming Keep the Flavour In?
Steam cooks food at boiling temperature without dissolving its flavour away into water.
Let’s go →A pinch of carbon changes everything
What Makes Steel Stronger Than Iron?
Steel is iron with a small, carefully controlled amount of carbon, which jams the metal's layers and makes it strong.
Let’s go →The wick drinks its own fuel
Why Does a Candle Burn for Hours?
A candle burns steadily because the flame melts the wax and the wick draws exactly as much as it can burn.
Let’s go →Glowing gas, not glowing wood
What Actually Is a Flame?
A flame is gas driven out of the fuel, glowing hot as it joins with oxygen from the air.
Let’s go →It is mostly trapped air
Why Is Wool So Warm?
Wool keeps you warm because its kinked fibres trap still air, and still air is very bad at carrying heat away.
Let’s go →The line carries on
How Can a Number Be Less Than Nothing?
Negative numbers exist because the number line does not stop at zero; it carries straight on.
Let’s go →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.
Let’s go →Escaping one at a time
Where Does a Puddle Go?
Puddles vanish because fast-moving surface molecules escape into the air as vapour.
Let’s go →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.
Let’s go →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.
Let’s go →A blanket that lets light in
How Does the Air Keep Earth Warm?
Greenhouse gases let sunlight in but trap the heat radiating back out, keeping Earth far warmer than it would be.
Let’s go →Air that will not leave
What Makes a Heatwave?
A heatwave happens when sinking, stuck air blocks clouds and lets heat build day after day.
Let’s go →Sorted by weight
What Is Inside the Earth?
Earth has layers because heavy metal sank to the centre while it was still molten.
Let’s go →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.
Let’s go →Nothing is permanent
Can a Rock Turn Into a Different Rock?
Rocks continually change type, as heat, pressure and weathering recycle them into one another.
Let’s go →Land and sea disagree
Why Is It Windy at the Beach?
Land warms faster than water, so air rises over the land and pulls a breeze in from the sea.
Let’s go →The ground is still catching up
Why Is the Hottest Month Not the Longest Day?
The hottest weeks come after midsummer because land and sea are still absorbing more heat than they lose.
Let’s go →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.
Let’s go →Pressure finding a way out
Why Do Volcanoes Erupt?
Volcanoes erupt when buoyant molten rock and expanding gas force their way to the surface.
Let’s go →Fire as a gardener
Why Do Some Forests Need to Burn?
Some forests depend on regular small fires, and preventing them lets fuel build until the fire is catastrophic.
Let’s go →Air evening things out
What Makes Wind Blow?
Wind is air flowing from high pressure to low pressure because the Sun heats unevenly.
Let’s go →Losing your warm coat of air
Why Does Wind Make You Colder?
Wind blows away the warm layer of air your skin has heated, so you lose heat much faster.
Let’s go →The one blush you cannot fake
Why Do You Go Red When You Are Embarrassed?
Blushing is blood vessels in your face opening on their own — a signal you cannot start, stop, or fake.
Let’s go →A reflex for fur you lost
Why Do You Get Goosebumps?
Goosebumps are tiny muscles pulling your hairs upright, a leftover reflex from furry ancestors.
Let’s go →Muscles working for the heat, not the movement
Why Do You Shiver When You Are Cold?
Shivering makes your muscles do pointless work on purpose, because most of what a muscle produces is heat.
Let’s go →More than a wrapper
What Does Your Skin Do?
Skin keeps things out, controls temperature, senses the world and repairs itself.
Let’s go →Cooling by evaporation
Why Do We Sweat?
Sweating cools you because evaporating water takes heat from your skin.
Let’s go →A comb and a scraper
How Does a Cricket Chirp?
A cricket sings by scraping a row of ridges on one wing with a hard edge on the other, and hears with its knees.
Let’s go →A nose with forty thousand muscles
What Can an Elephant Do With Its Trunk?
An elephant's trunk is a boneless nose and upper lip with tens of thousands of muscles, used to breathe, drink, grab, smell and talk.
Let’s go →Holding onto still air
Why Do Animals Have Fur?
Fur works by trapping a layer of still air against the skin, and animals fluff it, shed it and grow it back as the seasons change.
Let’s go →Turning the engine down
Why Do Animals Hibernate?
Hibernating animals slow their whole body down to survive winter without food.
Let’s go →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.
Let’s go →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.
Let’s go →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.
Let’s go →A wire crossed
Why Does Ice Cream Give You a Headache?
Brain freeze is a cold reflex in the roof of your mouth that your brain reports as head pain.
Let’s go →Ice leaving without melting
What Is Freezer Burn?
Freezer burn is ice escaping food as vapour without ever melting, leaving it dry.
Let’s go →Locking into a pattern
What Happens When Water Freezes?
Freezing locks water molecules into an open pattern that takes up more space.
Let’s go →Heat always moving in
Why Does Ice Cream Melt?
Ice cream melts because heat always flows from the warmer room into it.
Let’s go →Lowering the freezing point
Why Does Salt Melt Ice?
Salt lowers water's freezing point, so ice melts at temperatures below zero.
Let’s go →It steals heat faster
Why Does Metal Feel Colder Than Wood?
Metal feels colder because it conducts heat away from your hand much faster than wood.
Let’s go →Waves that overlap themselves
Why Does a Microwave Heat Unevenly?
Microwaves bounce off the metal walls and overlap, creating fixed hot and cold spots.
Let’s go →Steam bursting out
Why Does Popcorn Pop?
Popcorn pops when trapped water turns to steam and bursts the hard shell.
Let’s go →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.
Let’s go →Making water boil hotter
How Does a Pressure Cooker Cook Faster?
A sealed pot raises the pressure inside, so water boils hotter and food cooks faster.
Let’s go →Air losing its grip on water
Why Do Windows Fog Up?
Windows fog when warm moist air touches cold glass and its water condenses.
Let’s go →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.
Let’s go →Metal and protein shaking hands
Why Does Food Stick to the Pan?
Proteins bond to hot metal and release only once a crust has formed underneath.
Let’s go →Sugars and proteins reacting
Why Does Toast Go Brown?
Toast browns because heat makes sugars and proteins react into new flavour compounds.
Let’s go →Cooling and catching
Why Do We Yawn?
Yawning appears to cool the brain, and it spreads contagiously between people.
Let’s go →Turning speed into heat
How Does Rubbing Stop a Car?
Brakes stop a car by squeezing pads onto a spinning disc, turning the car's movement into heat.
Let’s go →A shove converted to a spin
How Does a Bang Turn a Wheel?
A car engine burns fuel to shove a piston, and a crankshaft converts that straight push into a spin.
Let’s go →Carrying heat out, not cold in
How Does a Box Make Itself Cold?
A fridge does not make cold: it carries heat out of the box using a gas that is squeezed hot and expanded cold.
Let’s go →Something has to break first
Why Do Fuses Blow?
A fuse is a thin wire built to melt when too much electricity flows, breaking the circuit before anything else can burn.
Let’s go →A fan and a hot wire, in that order
What Is Inside a Hairdryer?
A hairdryer is a fan and a coil of thin wire — and hair dries because moving air carries water away, not because the air is hot.
Let’s go →The same bag, holding less
Why Does Hot Air Lift a Balloon?
A hot-air balloon rises because heating the air drives some of it out, leaving the balloon lighter than the air around it.
Let’s go →Steam that flips a switch
Why Does a Kettle Switch Itself Off?
A kettle stops because steam runs down a hidden tube to a strip of two metals, which bends and snaps the switch open.
Let’s go →A wire too hot to stay dark
How Does Electricity Become Light?
An old bulb glows because a thin wire resists the current and gets white-hot; an LED makes light directly.
Let’s go →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.
Let’s go →Splitting atoms to boil a kettle
How Does Nuclear Power Work?
Nuclear power splits heavy atoms to release heat, which boils water and drives a turbine like any other station.
Let’s go →Almost all of them boil water
How Does a Power Station Work?
Most power stations burn or split something to boil water, and the steam spins a turbine that turns a generator.
Let’s go →A switch that feels the room
How Does a Heater Know When to Stop?
A thermostat is just a switch that temperature opens and closes, which is why a room drifts slowly above and below the number you set.
Let’s go →