Shapes

Gravity pulls from all sides

Why Is Every Planet a Ball?

Planets are round because gravity pulls equally from all sides, and rock cannot hold any other shape at that size.

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A hidden middle

What Keeps Things From Falling Over?

Things stay upright while their centre of gravity stays over their base.

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Bending light on purpose

How Do Lenses Work?

A lens bends light because its curved shape slows different parts of a beam by different amounts.

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A very smooth wall

How Do Mirrors Work?

Mirrors work because their surface is smooth enough to bounce light without scrambling it.

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The same climb, stretched out

Why Are Ramps Easier?

Ramps make lifting easier by spreading the same climb over a longer distance.

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Light coming back

Why Can You See Yourself?

Reflection is light bouncing off a surface at the same angle it arrived.

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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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Light in a straight line

Why Do Shadows Happen?

A shadow is the place light could not reach because something was in the way.

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The same atom, two arrangements

Why Is Diamond Hard and Pencil Lead Soft?

Diamond and pencil lead are the same atom. Only the pattern of the bonds is different, and it changes everything.

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Light finds nothing to grab

Why Can You See Through Glass?

Light goes through glass because there is nothing in it that can absorb visible light, and nothing inside to scatter it.

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Turn, not length

What Is an Angle Actually Measuring?

An angle measures amount of turn between two directions, so longer arms do not make a bigger angle.

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Counting squares, quickly

Why Do We Multiply to Find Area?

Area is the number of squares covering a shape, and multiplying rows by columns counts them fast.

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Counting without counting

Why Are Rows and Columns Useful?

An array arranges things in rows and columns so you can multiply instead of count.

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Two numbers, one place

How Do You Describe Exactly One Square?

Coordinates pin down a place with two numbers: how far across, then how far up.

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Bigger bottom, smaller piece

Why Is a Third Bigger Than a Quarter?

A third beats a quarter because the bottom number counts cuts, and more cuts make each piece smaller.

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Seeing beats reading

Why Draw Numbers as a Picture?

Graphs work because eyes compare lengths and heights far faster than they read columns of numbers.

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Two equal shares

What Does Half Mean?

A half is one of two pieces that are exactly the same size.

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Everything divided by the same number

How Does a Map Fit a Country on a Page?

A map shrinks every distance by the same factor, which is what keeps the shapes right.

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Everyone agreeing

Why Do We Measure With Units?

Measuring means counting how many agreed units something is.

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Can everyone find a partner?

Odd and Even Numbers

Even numbers split into pairs with none left over; odd numbers always leave one.

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Something that repeats

What Is a Pattern?

A pattern is a repeating rule, and finding the rule lets you predict what comes next.

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The fence and the field

How Are Area and Perimeter Different?

Perimeter is the distance round the edge and area is the space inside, and one does not fix the other.

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Every circle's hidden number

What Is Pi and Why Does It Never End?

Pi is the number of diameters that fit around any circle, and it is the same for all of them.

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No rectangle but a line

Which Numbers Refuse to Split?

Primes are numbers that cannot be split into equal groups, so they only ever form one long row.

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One of four

What Is a Quarter?

A quarter is one of four exactly equal shares of a whole.

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Length halves, weight drops by eight

Why Is a Model Never Quite Right?

Scaling changes length, area and volume by different factors, so models never behave like the real thing.

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Sorted by rules

Why Do Shapes Have Names?

Shape names are definitions — a checklist of sides, angles and corners.

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A third direction

What Makes a Shape 3D?

A solid shape adds a third direction to a flat one, which is what gives it faces, edges and corners.

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Two matching halves

What Is Symmetry?

Symmetry means a shape matches itself when folded or turned.

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Sharing between three

What Is a Third?

A third is one of three exactly equal shares — and it never divides evenly in decimals.

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Stacking layers of squares

How Much Does a Box Actually Hold?

Volume is the number of unit cubes that fit inside a space, found by stacking layers of area.

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Atoms in formation

What Is a Mineral?

A mineral is a natural solid with a fixed recipe and a repeating atomic pattern.

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Stiff and springy together

What Are Bones Made Of?

Bone mixes hard mineral with flexible protein, giving strength without brittleness.

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Seven metres of grabbing

Why Are Your Intestines So Long?

Your intestines are long because food is only absorbed at the wall, and length, folds and fuzz all buy more wall.

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Half a tennis court, folded up

Why Are Lungs Spongy Instead of Hollow?

Lungs are spongy because oxygen can only cross where air touches blood, and folding gives an enormous amount of touching.

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A toolkit in your mouth

Why Do Teeth Have Different Shapes?

Teeth have different shapes because cutting, tearing and grinding need different tools.

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Instinct plus practice

How Do Birds Build Nests?

Birds build nests by instinct, and improve at it with practice.

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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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One structure, many jobs

Why Do Birds Have Feathers?

Feathers are branching structures that zip into light, stiff sheets for flight, warmth and display.

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Only some threads are glued

Why Don't Spiders Stick to Their Own Webs?

Spiders avoid sticking because only some web threads are coated in glue.

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Air pushing back

Why Does a Balloon Stay Blown Up?

A balloon stays inflated because air molecules inside push outward against the stretched rubber.

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The laziest possible shape

Why Are Bubbles Always Round?

Bubbles are round because a sphere uses the least surface to hold the air inside.

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Atoms joining a queue

How Do Crystals Grow?

Crystals grow as atoms leave a solution and lock into a repeating pattern.

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Sound coming back

What Is an Echo?

An echo is sound reflecting off a surface and returning to you delayed.

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Far, hard and facing you

Why Do Canyons Echo So Well?

Canyons echo because their walls are far away, hard and steeply angled back at you.

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Nothing left to absorb sound

Why Are Empty Rooms So Echoey?

Empty rooms echo because there is nothing soft left to absorb the reflected sound.

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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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Trading height for distance

Why Does a Paper Plane Glide?

A paper plane glides by falling forward slowly while air pushes up on its wings.

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Colours bending differently

What Does a Prism Do?

A prism splits white light into colours because each colour bends differently.

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Blocking light, close and far

How Do Shadow Puppets Work?

Shadow puppets work because blocked light spreads out, so nearer objects cast bigger shadows.

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Thousands of tiny hooks

How Does Velcro Stick?

Velcro works because thousands of stiff hooks catch in thousands of soft loops.

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Under the floor and back

Where Do Escalator Steps Go at the Top?

Escalator steps never end: they flatten at the top, travel back underneath, and come up again.

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A set of heights, not a shape

Why Does Only One Key Fit?

Only one key fits because each notch must lift its own pin to exactly the right height.

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Two levers and a travelling point

Why Do Scissors Cut When One Blade Cannot?

Scissors cut because two levers meet at one travelling point, squeezing the material from both sides at once.

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Millions of tiny lights

Why Are Pictures Made of Dots?

Screens show pictures as a grid of dots mixing red, green and blue, redrawn fast enough to look like motion.

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A ramp wrapped round a stick

Why Is a Screw So Hard to Pull Out?

A screw is a ramp wrapped round a stick — it turns many easy turns into one enormous squeeze.

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Cones, not lips

Why Do Train Wheels Never Fall Off?

Train wheels stay on because they are cones on a shared axle, so drifting sideways makes them steer back to centre.

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One push, turned sideways

Why Does a Sharp Edge Cut So Easily?

A sharp edge cuts because a wedge turns your downward push into a much larger sideways push that splits things apart.

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A Y-channel and a wedge

What Actually Joins a Zip?

A zip works because the slider forces hooked teeth together one way and wedges them apart the other.

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