Pushes & pulls

Leftover bricks

What Are Asteroids?

Asteroids are rocky leftovers from when the planets were being built.

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Not what you think

Why Do Astronauts Float?

Astronauts float because they and their ship are falling around Earth together.

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Gravity turned all the way up

What Is a Black Hole?

A black hole is matter packed so tightly that light cannot escape its pull.

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An island of stars

What Is a Galaxy?

A galaxy is an enormous gravity-bound island of stars, separated from other galaxies by near-total emptiness.

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Yes, lots

Is There Gravity in Space?

Gravity fills all of space; it just weakens with distance and never quite stops.

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A true space story

Where the Moon Came From

A giant smash long ago threw up the rock that became our Moon.

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Leave most of the ship behind

How Did the Astronauts Get Back Off the Moon?

Getting off the Moon needed only a small rocket, because lunar gravity is weak and there is no air to fight.

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A star nursery

What Is a Nebula?

Nebulae are giant space clouds where stars are born and where they die.

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Falling without ever landing

What Is an Orbit?

An orbit is a permanent fall: move sideways fast enough and the ground curves away as fast as you drop towards it.

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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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Pushing on nothing

How Do Rockets Launch?

Rockets fly by hurling hot gas downward — the recoil lifts them.

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Fast enough to miss

How Do Satellites Stay Up?

Satellites stay up by moving sideways so fast they keep missing Earth.

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Billions of orbiting snowballs

What Are Saturn's Rings Made Of?

Saturn's rings are billions of separate ice chunks orbiting individually, not a solid hoop.

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Falling forever

Why Planets Orbit the Sun

Planets fall toward the Sun but move sideways fast enough to keep missing it.

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A shell of debris

What Happens to Old Satellites?

Old satellites become debris that keeps orbiting, and at eight kilometres a second even tiny fragments are lethal.

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Home at 28,000 km/h

Living on the Space Station

Life on the space station means everything you do has to be redesigned for free fall.

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An invisible ocean

Air Is Pressing on You

Air has weight, and the whole atmosphere presses down on everything.

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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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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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Passing motion along

What Happens When Things Crash?

In a collision, movement is passed between objects and never simply vanishes.

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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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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.

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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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Why things stop

What Is Friction?

Friction is the grip between two surfaces that turns motion into heat.

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Trading speed for strength

How Do Gears Work?

Gears let you trade speed for force by pairing wheels of different sizes.

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The pull you never notice

What Is Gravity?

Gravity is the pull every object with mass has on every other object.

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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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Nothing changes for free

Why Do Things Keep Moving?

Inertia is an object's refusal to change speed or direction on its own.

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Trading distance for force

How Do Levers Work?

A lever lets a small push move a big load by trading distance for force.

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Invisible reach

How Do Magnets Work?

A magnet works because its atoms are all lined up in the same direction.

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Our planet is a magnet

Why Does a Compass Point North?

Earth's liquid iron core makes a magnetic field that swings compass needles north.

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Mass times speed

Why Are Heavy Things Hard to Stop?

Stopping something depends on both its mass and its speed, and spreading the stop over time reduces the force.

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Air shoved out of the way

How Does a Parachute Slow You Down?

A parachute slows a fall by making you shove far more air aside, and that air pushes back hard.

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A reliable swing

Why Does a Pendulum Keep Time?

A pendulum keeps time because its swing length depends only on the string, not the size of the swing.

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Force, spread out

What Is Pressure?

Pressure is force divided by area — a small area concentrates the same push.

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Sharing the load

How Do Pulleys Help?

Pulleys split a heavy load across several rope sections so each pull is lighter.

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Newton's third law

Every Push Has a Push Back

Forces always come in pairs — push anything and it pushes you back.

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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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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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Storing a push

How Do Springs Work?

A spring stores energy when squashed and gives it back when released.

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Rubbed the wrong way

Why Do You Get Shocks?

Static shocks happen when rubbing moves electric charge, and it jumps back all at once.

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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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Empty space cannot push

What Does Nothing Actually Do?

A vacuum does nothing at all; the interesting effects all come from the pressure of whatever surrounds it.

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Wobbling back to the middle

Why Do Things Vibrate?

Vibration happens when something springy is pushed out of shape and overshoots on the way back.

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Rolling beats dragging

Why Are Wheels So Good?

Wheels work because rolling replaces sliding friction with almost none.

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Wrong-sized atoms get in the way

Why Is Pure Gold Too Soft for a Ring?

Mixing metals makes them stronger, because odd-sized atoms jam the neat rows that let metal bend.

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Twist turns short fibres into long ones

How Does Fluff Become Thread?

Thread is short fibres twisted until friction holds them together as one continuous strand.

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Flow into every crevice, then stop flowing

How Does Glue Hold Two Things Together?

Glue must first be runny enough to fill every tiny pit in both surfaces, and then stop being runny.

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A thread made from nothing that grew

Why Was Nylon Invented?

Nylon is a made fibre: long molecule chains pulled straight, giving thread that is strong, endless and rot-proof.

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Twist, and twist again

Why Is a Rope Stronger Than Its Threads?

A rope is strong because twisting makes every fibre squeeze its neighbours, so pulling only tightens the grip.

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Tangled springs

Why Does Rubber Bounce Back?

Rubber springs back because its long tangled molecules straighten when pulled and coil up again when let go.

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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.

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A bundle of drinking straws

Why Does Wood Split One Way?

Wood splits along the grain because it is a bundle of water-carrying tubes, easy to part and hard to cut across.

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Size and heaviness are separate

Why Is a Big Thing Not Always Heavy?

Big does not mean heavy, because weight depends on how tightly matter is packed, not on size.

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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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Because it was one

Why Does the Map Look Like a Jigsaw?

South America and Africa fit together because they really were joined, and the sea floor between them is still growing.

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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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Rock finally slipping

Why Does the Ground Shake?

Earthquakes happen when stuck slabs of rock suddenly slip past each other.

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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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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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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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Crust crumpling

How Do Mountains Grow?

Mountains form where colliding plates crumple the crust upward.

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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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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 spin tipped upright

How Does a Tornado Form?

A tornado is a horizontal rolling column of air tipped upright and stretched by a storm.

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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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Pressure finding a way out

Why Do Volcanoes Erupt?

Volcanoes erupt when buoyant molten rock and expanding gas force their way to the surface.

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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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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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A backstop for your fingertip

What Are Fingernails For?

Fingernails are a hard backstop that lets your soft fingertip press against something, making fine touch and picking things up possible.

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Only ever pulling

How Do Muscles Move You?

Muscles move you by pulling, which is why they come in opposing pairs.

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Blasting the nose clear

Why Do We Sneeze?

A sneeze is an automatic blast of air that clears irritants from your nose.

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Several senses at once

How Does Touch Work?

Touch is several different senses working together in your skin.

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Everything about it is built for lightness

How Does a Bird Stay Up?

A bird flies on curved wings that bend passing air downwards, carried by hollow bones and enormous chest muscles.

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Seven bones, same as yours

Why Is a Giraffe's Neck So Long?

A giraffe reaches leaves nothing else can, and needs an extraordinary heart and valves to pump blood that high.

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Getting your energy back

Why Does a Kangaroo Hop?

A kangaroo's tendons store and return energy like springs, so hopping costs it barely more at speed than at a crawl.

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One foot, one shell, no hurry

How Does a Snail Carry Its House?

A snail glides on a single muscular foot over a trail of slime, inside a shell that grew from its own body.

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A whole body doing the work of feet

How Does a Snake Move With No Legs?

A snake moves by pressing its body against the ground and pushing sideways, with ribs and scales doing the work of legs.

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Nobody is in charge

How Does a Flock Turn All at Once?

A flock, shoal or swarm moves as one because each animal follows a few simple rules about its nearest neighbours.

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One part, a dozen jobs

What Is a Tail For?

Tails do whatever an animal most needs — steering, balancing, gripping, signalling or keeping warm.

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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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A magnet inside a bigger magnet

How Does a Compass Work?

A compass needle is a magnet that lines up with Earth's magnetic field.

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A skin that shoves the air

How Does a Drum Make a Sound?

A drum's stretched skin is hit, shudders, and shoves the air — with the shell shaping how long and low it rings.

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Ridges that grip and feel

Why Do We Have Fingerprints?

Fingerprint ridges improve grip on wet surfaces and sharpen your sense of touch.

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A squashed cable

Why Does Your Foot Go to Sleep?

A squashed nerve stops sending signals, and pins and needles are those signals restarting.

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Iron, made temporarily magnetic

Why Do Magnets Stick to the Fridge?

Magnets stick to fridges because the door's steel becomes temporarily magnetic itself.

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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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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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Tangled chains straightening out

Why Do Rubber Bands Snap Back?

Rubber snaps back because stretching straightens its tangled molecule chains.

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All the force in one line

Why Is a Sharp Knife Safer Than a Blunt One?

A sharp knife needs less force because all the push lands on a very thin edge.

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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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Pushing in time

How Do You Make a Swing Go Higher?

Pumping works because small pushes timed to a swing's natural rhythm build up over many arcs.

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Your brain saw it coming

Why Can't You Tickle Yourself?

You cannot tickle yourself because your brain predicts your own touch and cancels the surprise.

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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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Throwing air downwards

Why Does a Wing Hold a Plane Up?

A wing holds a plane up by deflecting air downward; the air pushes back, and that push is lift.

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Constant, invisible steering

Why Does a Moving Bike Stay Up?

A moving bike stays up because tipping steers the front wheel into the fall, and the curve pushes it upright again.

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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.

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A see-saw with a concrete end

Why Doesn't a Crane Tip Over?

A crane stays up because it is a see-saw: concrete on the short arm balances the load on the long one.

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Oil that refuses to be squashed

How Does a Digger Lift So Much?

A digger is strong because oil cannot be squashed, so a small piston pushing hard becomes a big piston pushing enormously.

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Only lifting the difference

Why Does a Lift Need a Counterweight?

A lift uses a counterweight so the motor only has to lift the difference, not the whole car.

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Stopping the cabin spinning

Why Does the Little Tail Rotor Matter?

A helicopter needs a tail rotor because turning the main blades twists the body the opposite way.

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Sheets that slide off

Why Does a Pencil Leave a Mark?

A pencil writes because graphite is carbon in flat, slippery sheets, and rough paper scrapes them off as you drag it.

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Two pushes and a leftover

How Does a Boat Sail Into the Wind?

A sailboat goes upwind because the sail pushes sideways, the keel blocks sideways, and the leftover is forward.

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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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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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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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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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The room does the pushing

Why Does Suction Pick Things Up?

Nothing sucks: a vacuum cleaner lowers the pressure inside, and the room's own air pushes dust in.

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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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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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