Interactive principle library
See each step. Understand why.
Watch the explanation, then change the model yourself.FOLLOW YOUR CURIOSITY
What will you see differently?
Familiar things. Unexpected explanations.
125 topics
About the age guide
Cards suggest a starting age for following the main explanation, not a measure of ability. Younger viewers can watch with someone; equations and technical detail are optional.
Mechanisms & motion
Bicycle gears
Why does changing gear make pedaling easier?
Light & waves
Rainbows
Why does a rainbow appear in that direction?
Mechanisms & motion
Zipper
How does a zipper close with one pull?
Earth & astronomy
Moon phases
Why does the Moon change shape?
Electricity & magnetism
Laser printing
How does a beam of light become a printed word?
Light & waves
Active noise control
Can adding sound make things quieter?
Mechanisms & motion
The pendulum
Where does a pendulum keep time?
Computing & communication
JPEG compression
When a photo shrinks, what survives?
Mechanisms & motion
Four-stroke engine
How does combustion become rotation?
Math & systems
Higher dimensions
What does one more dimension add?
Electricity & magnetism
Lithium-ion battery
What does a rechargeable battery store?
Computing & communication
Training & generation
How does a model learn the next token?
School safety
What can we play at break?
Find the right place for your game
School safety
What can I do after causing harm?
Stop the harm, then make a real repair
School safety
When you see someone being hurt
Skip the crowd. Find an adult who can help.
School safety
When someone says stop
Playing together takes two willing people
School safety
School stairs
Do not give that push on the stairs
School safety
Hallway corners
Who is around the corner?
School safety
Leave the chair in place
A steady seat for a friend
School safety
Keep feet out of the way
I was only joking
Mechanisms & motion
Metro Construction
How is a metro built beneath a city?
Heat & fluids
Aquarium air pump
How does oxygen in air enter the water?
Heat & fluids
Sewer
The water drains away. Why does the smell stay out?
Heat & fluids
Whirlpools
From a bathtub to an ocean: why does water swirl?
Mechanisms & motion
Trams
Why does a tram wear a little ponytail on its roof?
Mechanisms & motion
The Metro
In the dark underground, how does a metro find its way?
Mechanisms & motion
Bike Balance
Why doesn't a moving bicycle fall over?
Mechanisms & motion
Petrol engine
How does one drop of petrol push a whole car?
Electricity & magnetism
Electric Cars
Without drinking fuel, where does an electric car get its strength?
Mechanisms & motion
Trains
How does a train of thousands of tonnes run so fast?
Mechanisms & motion
Tunnel Boring
Who digs the metro tunnels underground?
Mechanisms & motion
Sea tunnel
How do you build a tunnel under the sea?
Mechanisms & motion
Sea bridge
How does a sea bridge stand in the water?
Mechanisms & motion
Airports
Why does an airport need to be so big?
Mechanisms & motion
Bearings
Why does a ring of steel balls make wheels spin so freely?
Light & waves
Ear thermometer
Reading heat without sending a beam
Electricity & magnetism
Body fat scale
How do four metal pads become a body-fat reading?
Heat & fluids
Jellyfish
Why can a jelly keep gaining speed after its bell stops?
Light & waves
Instant camera
A darkroom inside the sheet
Light & waves
SLR & mirrorless
Before capture, how do we see?
Light & waves
Myopia-control lenses
Why add another optical signal after correcting the blur?
Computing & communication
eSIM
Without a SIM tray, where did the SIM go?
Computing & communication
CPU, GPU and NPU
Why do we need three kinds of processor for one task?
Computing & communication
Cells and handover
Why doesn't a call drop while you move?
Computing & communication
4G and 5G
Where does 5G speed come from?
Computing & communication
Mobile roaming
Abroad, how does your phone still know who you are?
Mechanisms & motion
Gyroscope
How does a phone know it has turned?
Electricity & magnetism
Computer touchpad
How does a light glide become a cursor movement?
Heat & fluids
Capillary action
Why does water climb a paper towel on its own?
Heat & fluids
Evaporation and condensation
Where does the water on a window come from?
Light & waves
Pitch
Why are some sounds high and others low?
Mechanisms & motion
Spinning tops
Why doesn't a spinning top fall over?
Electricity & magnetism
Simple circuits
How does one switch light up a bulb?
Mechanisms & motion
Pulleys and ropes
How does a little wheel at the top raise a flag?
Electricity & magnetism
Static electricity
Why can a rubbed comb pick up paper bits?
Heat & fluids
Thermal expansion
Why do rails have gaps and thermometers move?
Heat & fluids
Dissolution
Where does a spoonful of sugar go in water?
Light & waves
Echo
Why does your voice come back after you shout?
Electricity & magnetism
Compass
Why does a compass needle keep returning to one direction?
Heat & fluids
How plants move water
Without a heart or pump, how does a plant lift water to its leaves?
Mechanisms & motion
Earthquakes and buildings
Why can a building sway more than the ground?
Mechanisms & motion
Seesaw
How can sitting farther out lift someone heavier?
Electricity & magnetism
Magnet
How can a magnet pick up a paper clip through paper?
Light & waves
Shadow
Why is a shadow sometimes long and sometimes short?
Heat & fluids
Floating and sinking
How can the same clay float after changing shape?
Mechanisms & motion
Keyboard switches
One press. What changes inside a switch?
Weapons & safety
Landmines
Why can danger outlast a war?
Weapons & safety
AK-47
How does a pulse of gas become a return journey?
Mechanisms & motion
Helicopter
How does a wing take off without a runway?
Weapons & safety
Hydrogen bomb
Why can joining light nuclei release energy?
Weapons & safety
Atomic bomb
How can one nuclear fission lead to the next generation?
Electricity & magnetism
NFC
How does a tag answer without a battery?
Light & waves
Double-slit interference
Why does a second slit make some places darker?
Mechanisms & motion
Excavator
How does oil lift a bucket of earth?
Earth & astronomy
Tides
Why does water bulge on the far side too?
Computing & communication
Packet routing
How do packets cross a changing network?
Heat & fluids
Diffusion
Why does color spread without a current?
Heat & fluids
Brownian motion
Why does a particle move in a still fluid?
Computing & communication
Database index
How does a database find a row without reading the whole table?
Mechanisms & motion
Clock escapement
How does an escapement give a clock its beat?
Computing & communication
Logic gates
Logic gates: how voltage becomes zero and one
Computing & communication
Public-key cryptography
How can a public key help keep a message private?
Electricity & magnetism
Solar panels
How do solar cells send sunlight into a circuit?
Heat & fluids
Convection
How does heat set a fluid in motion?
Electricity & magnetism
Rectifier
Why does the load keep its polarity when AC reverses?
Mechanisms & motion
Sewing machine
How does one needle interlock two threads?
Electricity & magnetism
Induction cooktop
Why does heat begin in the pan?
Computing & communication
Hash
Why can one changed bit alter an entire digest?
Electricity & magnetism
Buck converter
How do pulses become a steady lower voltage?
Light & waves
Compound microscope
Does a bigger image always reveal more detail?
Heat & fluids
Airfoil lift
Air has no appointment at the trailing edge
Computing & communication
QR Code
How does a tiny grid hold an entire URL?
Light & waves
Speaker
How does a speaker turn current into sound?
Electricity & magnetism
Wireless charging
Wireless charging: how does power cross a gap?
Mechanisms & motion
Pin-tumbler lock
How does a small key let a lock cylinder turn?
Light & waves
Ultrasound imaging
How do echoes become an image of the inside?
Mechanisms & motion
Car differential
Why can driven wheels turn at different speeds?
Computing & communication
Error correction
How can a flipped data bit find its way back?
Heat & fluids
Flow speed and pressure
Does faster water always mean lower pressure?
Light & waves
Doppler effect
Why does the pitch change when the source keeps its beat?
Electricity & magnetism
Induction motor
Induction motor: why stay slightly behind?
Light & waves
Wave interference
When the string is straight, where are the waves?
Heat & fluids
Water hammer
Why can a sudden valve closure jolt a water pipe?
Mechanisms & motion
Car suspension
Does a softer suspension always ride better?
Light & waves
Diffraction
Why does light spread out after a narrow slit?
Computing & communication
Memory and cache
Why can a cache miss when there is still empty space?
Electricity & magnetism
Electric generator
Why does a turning loop generate electricity?
Heat & fluids
Siphon
How can water climb before flowing downhill?
Mechanisms & motion
Ball bearing
How does a ball help a shaft turn freely?
Earth & astronomy
Seasons
How does a tilted axis create the seasons?
Light & waves
Polarization
How can adding a polarizer let more light through?
Computing & communication
CPU instruction pipeline
If one instruction is no faster, why is the program faster?
Electricity & magnetism
Electrical transformer
The wires never meet. How does voltage cross?
Mechanisms & motion
Hydraulic brakes
How does a squeeze grip a distant rotor?
Computing & communication
Binary addition
How do zeros and ones add up?
Light & waves
Optical fiber
What keeps light inside a glass fiber?
Mechanisms & motion
Planetary gearing
How can one gearset give different speeds?
Light & waves
Camera lenses
How does light become an image?
Light & waves
Aperture and depth of field
Where does background blur happen?
Heat & fluids
Refrigeration
Where does the heat in a fridge go?
Math & systems
GPS positioning
How do satellites find you?
Computing & communication
Loading a webpage
What happens after you press Enter?
Math & systems
Lift scheduling
Why are we still waiting for the lift?
Math & systems
Phantom traffic jams
No accident. So why the traffic jam?
Heat & fluids
Humidifier
How does water fly into dry winter air?
A different path to something new.
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