Physics
Fields, forces and energy.
Field lines · the magnetic field
Slide and rotate bar magnets and watch the iron filings, field lines and field-strength map rearrange themselves.
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Orbit · orbital mechanics
A gravity assist like Voyager's, a Hohmann transfer, docking with a space station, Kepler's laws and the Lagrange points. Plus an N-body sandbox with colliding galaxies.
Open the experimentEnergy · kinetic and potential
A skater on a track you build yourself, and a pendulum. Watch live as energy turns from potential into kinetic and friction turns it into heat.
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Chaos · the double pendulum
Release two pendulums from almost exactly the same spot, and a few seconds later they move completely differently. See the butterfly effect and a map of chaos.
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Gas · molecules and pressure
Hundreds of molecules bouncing around in a box. Heat them up, squeeze them with a piston, and test the gas laws and the Maxwell speed distribution.
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Buoyancy · Archimedes' principle
Drop wood, ice and gold into water. See what floats, what sinks and how much water each object displaces. There's also a boat to sink.
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Circuit · current and voltage
Build your own circuit from batteries, bulbs, diodes and switches. Watch the current flow and measure it with an ammeter.
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Radioactivity · glowing mysteries
A Geiger counter, paper and lead shields, atoms decaying live and carbon-14 dating, doses from a banana to a CT scan, and Marie Skłodowska-Curie's polonium and radium.
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Relativity · time that runs differently
A light clock and muons from space, a train struck by lightning and a Minkowski diagram, the twin paradox, E = mc², and gravity that slows down time in GPS.
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Quanta · particles as waves
Electrons passing one at a time through two slits, the photoelectric effect, orbitals in 3D, tunneling, uncertainty, entanglement and the Hamiltonian: draw a potential well and see the allowed energy levels.
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Heat · how a heat pump works
A house through a thermal camera, a fridge and a heat pump step by step, COP in a Polish winter, the Carnot cycle and entropy — or why time runs in only one direction.
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Lightning · charges and sparks
Field lines around charges, a balloon stuck to the wall, an electroscope, a Faraday cage and a capacitor — and then a storm: a stepped leader, thunder and where to take shelter.
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Motion and forces · Newton, live
Newton's laws and adding forces, a projectile shot at a hoop on different planets, friction on a slope and braking distance, collisions and a crash test, a skydiver and circular motion.
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Vibrations and resonance · everything that swings
A spring and a pendulum on an oscilloscope, damping like in shock absorbers, resonance and a game of pumping a swing, coupled pendulums, Chladni figures, buildings in an earthquake, and clocks from the pendulum to cesium.
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Elementary particles · what the world is made of
A journey from a grain of salt down to quarks, the Standard Model table, a collider with a detector and the hunt for the Higgs boson, antimatter, neutrinos and muons from space, and the history of the discoveries.
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Materials and structures · why bridges stay up
A testing machine for 9 materials, a truss-bridge designer with a truck, beams and I-beams, reinforced concrete, buckling and arches, the square–cube law, and lessons from disasters.
Open the experimentLight
Rays, lenses, waves and spectra.
Ray · the optical bench
Lenses, mirrors, prisms and a drop of water. Rays are traced according to Snell's law, including dispersion and total internal reflection.
Open the experimentLens · how an image forms
Move the candle and watch when the image is inverted, magnified or virtual. Look inside the eye, too, and fit glasses for a nearsighted person.
Open the experimentRefraction · light in another medium
Why does a teaspoon in tea look broken? Here you'll see how a wave slows down in water and glass and changes direction because of it.
Open the experimentSpectrum · what stars are made of
Every element has its own “barcode” of spectral lines. Split the light of lamps and of the Sun, then work out what a mystery star is made of.
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Laser · light in step
Stimulated emission and the lasing threshold, types of lasers from helium–neon to femtosecond, powers from a laser pointer to petawatts, and the story of the blue diode, without which there would be no Blu-ray and no white LEDs.
Open the experimentSound and waves
Vibrations we hear, and the math that describes them.
Spectrogram · see sound
Turn on the microphone, whistle or sing, and see your voice as a spectrum, a spectrogram and pulsar-style ridgelines. There's also a tuner and a sound generator for different instruments.
Open the experimentFourier · a sum of sines
Build a square wave from nothing but sine waves and listen to the result. Then draw any shape and watch rotating circles (epicycles) trace it out.
Open the experimentDoppler · when the source moves
Why does an ambulance siren change pitch as it drives past? Break the sound barrier, then measure the redshift of distant galaxies.
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String · standing waves
Pluck a virtual guitar string and listen. See which harmonics make up the sound and how guitarists play natural harmonics.
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Interference · waves on water
Drop two stones into a virtual bathtub and see where the waves reinforce each other and where they cancel out. Then shine a laser through two slits, one photon at a time.
Open the experimentTechnology
Machines that turn heat into motion.
Four-stroke · the combustion engine
Intake, compression, power, exhaust. Look inside the cylinder, turn the crankshaft by hand, and compare a gasoline engine with a diesel on a p–V diagram.
Open the experimentTwo-stroke · power on every turn
A piston that is its own valve. See how the mixture flows through the crankcase and the transfer ports. Finally, compare this engine with a four-stroke.
Open the experimentJet engine · thrust from hot gas
Start a turbofan engine, open the throttle and watch pressure, temperature and thrust rise. In the turbojet version you can switch on the afterburner.
Open the experimentSteam · the steam engine
A boiler, a slide valve, a flywheel and Watt's centrifugal governor. Add coal, change the load and see how the machine keeps its own speed in check.
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Induction · motor and generator
How does current turn into motion, and motion into current? Crank a generator, light a bulb and look inside a motor's commutator.
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Wing · lift
A wind tunnel in your browser. Change the airfoil shape and the angle of attack, watch the pressure, and push the wing into a stall.
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Clock · the mechanism
Gears, an anchor escapement and a pendulum. See how a spring and a few wheels measure out seconds, minutes and hours.
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Power plant · from coal to the wall socket
Follow energy from fuel to the wall socket in 23 types of power plant, from coal-fired to thorium and fusion*. Run the grid through a full day and night without letting the frequency drift away from 50 Hz.
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Computer · from transistor to processor
Build gates from transistors, an adder from gates and memory from flip-flops, then run your own program on a mini processor. Finally, the Enigma and the Polish codebreakers.
Open the experimentSpace
From our own backyard to the scale of galaxies.
Planetarium · the Solar System
The eight planets in their real positions today. You can scroll through time, fly to the planets and switch the distance scale.
Open the experimentGalaxies · islands of stars
Build a spiral galaxy, crash the Milky Way into Andromeda and find out why galaxies would fly apart without dark matter.
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Atmosphere · an ocean of air
A trip upward from the clouds to the auroras, the pressure that holds the Magdeburg hemispheres together, the color of the sky, the greenhouse effect, the halny (a Polish mountain foehn wind) and the atmospheres of other planets.
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Moon · phases, eclipses, saros
Today's phase, eclipses and the saros cycle, the Moon's birth in a collision with Theia, other moons of the Solar System, and the feather and hammer of Apollo 15.
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Seasons · the tilt of the axis
In winter the Earth is closest to the Sun. See where the seasons really come from, along with white nights and the polar day, and what the Great Year is.
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Stars · life and death
Pick a star's mass and live through billions of years with it: from the main sequence to a white dwarf, a neutron star or a black hole.
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Event horizon · the black hole
An image of a black hole computed ray by ray in your browser. See how gravity bends light and slows down time.
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Scale · from Planck to the cosmos
One scroll from the Planck length to the edge of the observable Universe. Plus Zeno's paradox, cosmological horizons, inflation, and a future in which we'll see only our own galaxy.
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Rocket · flight to orbit
Launch from Earth, drop a stage and reach a 400 km orbit. Then perform a Hohmann transfer to geostationary orbit.
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Space propulsion · how to brake in a vacuum
A map of engines from chemical rockets to solar sails, the de Laval nozzle, ion thrusters, nuclear propulsion and the key part: continuous thrust, the flip and braking on the way to Mars.
Open the experimentBiology
The molecules that life is built from.
Helix · the DNA double helix
A rotating 3D model of B-DNA with labeled structure. You can type in your own base sequence and watch an animation of replication.
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Cell · a city on a micro scale
Look inside an animal cell and a plant cell. Follow a protein from its gene to the membrane, and freeze mitosis in metaphase.
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Neuron · the nerve impulse
The Hodgkin–Huxley model, live. Stimulate a neuron, see the action potential and find out how myelin speeds up conduction.
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Heart · the pump of life
Four chambers, four valves and the conduction system. Watch blood flow in sync with an ECG trace.
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Eye · how we see
Rods and cones, color vision and color blindness, a blind spot you can find yourself, optical illusions, and animal eyes from the bee to the octopus.
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Lungs · breathing
The diaphragm and the bell-jar model, the bronchial tree, gas exchange in the alveoli, a virtual spirometer, and why it is CO₂, not a lack of oxygen, that makes us breathe.
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Blood · composition and types
Spin blood in a centrifuge, examine a smear under the microscope, see how hemoglobin releases oxygen, give a transfusion without agglutination and stop a bleed.
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Lymphatic system · the silent army
A second network of vessels, lymph nodes and swelling, macrophages in action, antibodies and immune memory, vaccination and herd immunity.
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Kidneys · bladder and blood pressure
A nephron filters 180 liters a day. Concentrate urine, fill the bladder, take blood pressure with a cuff and see how baroreceptors and the RAA system regulate it.
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Liver · a chemical factory
A liver lobule, blood sugar around the clock, ammonia turned into urea, bile and bilirubin, and the liver's remarkable ability to grow back.
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Nervous system · brain and reflexes
A map of the nerves and the brain, a reflex arc faster than pain, a reaction test in milliseconds, and the “fight or flight” switch.
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Evolution · natural selection
Little creatures with genes for speed, size and color compete for food. Watch their traits change from generation to generation.
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Ecosystem · who eats whom
A forest, a meadow and a stream through the seasons: mice, hares, roe deer, foxes, wolves and buzzards. Remove the wolves and watch a trophic cascade, then compare it all with the equations.
Open the experimentChemistry and matter
Elements and crystals.
Elements · the periodic table
All 118 elements. Each one has an animated Bohr model and its electron configuration, and you can filter by category.
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Crystal · from snowflake to diamond
Grow a snowflake, rotate crystal lattices in 3D, meet the seven crystal systems and quasicrystals, grow a salt crystal and see how X-rays reveal the atoms.
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Molecules · shapes in 3D
Rotate molecules from water to caffeine and fullerene. Build a shape from VSEPR theory and measure the angles between bonds.
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States of matter · solid, liquid, gas
Melt a crystal made of atoms, boil water on Mount Everest and find the triple point on a phase diagram.
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Acids and bases · the colorful pH scale
The pH scale from lemon to bleach, red-cabbage broth as an indicator, a titration with a burette and its curve, and the buffers that hold blood pH steady.
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Batteries · electricity from reactions
Build a voltaic cell and a lemon battery, look inside a lithium-ion battery, split water with electricity and protect a nail from rust.
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Fire · the chemistry of flame
The fire triangle and choosing an extinguisher, the zones of a candle flame, carbon monoxide and incomplete combustion, the flame colors of metals, and why dust can explode.
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Kitchen chemistry · cooking is an experiment
The Maillard reaction on a pork cutlet, a sous-vide egg, yeast and sourdough, pickling cucumbers, mayonnaise that won't split, and water boiling in a pressure cooker.
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Solutions · salt, water and membranes
Water takes a salt crystal apart into ions, solubility curves and “hot ice”, osmosis and desalination, a blood cell in different solutions, salt on the roads, and splitting a marker's ink into its colors.
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Reaction rates · from rust to explosions
Colliding molecules and activation energy, the catalytic converter in a car, enzymes with an optimum temperature, a race of chalk lump versus powder, and equilibrium in a syringe of NO₂.
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Plastics and polymers · chains that changed the world
Polymerization with beads, structure and a tensile test, recycling codes around the house, sorting plastics by whether they float, a recycling line and a deposit-return system, microplastics, and nature's own polymers.
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Air and smog · the chemistry of what we breathe
A jar of air and PM2.5 dust, a town in a valley with a temperature inversion and smoky old stoves, catalytic converters and AdBlue, acid rain, chlorine destroying ozone, and the Keeling curve and ocean acidification.
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Metals · from ore to alloy
The sea of electrons and malleability, the blast furnace and aluminum electrolysis, steel under the microscope and a forge with quenching, an alloy mixer from bronze to stainless steel, and the metals in your phone and their recycling.
Open the experimentMathematics
Simple rules, infinite complexity.
Fractal · the Mandelbrot set
An infinitely complex boundary from one simple formula. Dive a million times deeper and discover Julia sets.
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Life · Conway's game
Four simple rules give rise to gliders, guns and oscillators. Draw your own patterns and change the rules of the game.
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Pi · the number that is everywhere
Estimate π by throwing darts and dropping Buffon's needle, then compute thousands of digits and find your birthday in them.
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Fibonacci · the golden ratio
Why does a sunflower arrange its seeds at an angle of 137.5°? Rabbits, the golden spiral, pine cones, Pascal's triangle, and the Fibonacci sequence hidden in the Mandelbrot set.
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Derivative and integral · change and area
Graph any function you like, watch a secant become a tangent, and find areas with rectangles. See for yourself how π comes out of an integral.
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Trigonometry · the circle that draws waves
Drag a point around the unit circle and watch sine and cosine being born. Solve any triangle, measure the height of a tree, and repeat Eratosthenes' measurement of the Earth.
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Complex numbers · the plane and 3D
Multiplying by i is a 90° rotation. Euler's formula as a spiral in 3D, landscapes of complex functions with pits at the zeros and towers at the poles, and alternating current with phasors.
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Geometry · shapes that prove themselves
Animated proofs of Pythagoras' theorem, areas without memorizing formulas, compass-and-straightedge constructions, triangle centers with the Euler line, and Escher-style tessellations.
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Solids · unfold, measure, build
Unfold a solid into its net and see where surface area comes from. Why a pyramid is ⅓ of a prism, why there are only five Platonic solids, and how to slice a cube into a hexagon.
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Probability · chance has its laws
Dice and the law of large numbers, a Galton board with a bell curve, a playable Monty Hall game, the birthday paradox, a medical test and Bayes, and how to lie with a chart.
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Functions and growth · from a line to an explosion
A line and a parabola with draggable points, shifting graphs, exponential growth from rice on a chessboard to compound interest, logarithms with a working slide rule, and fitting models to data.
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Primes and ciphers · the atoms of arithmetic
The sieve of Eratosthenes and prime factorization, the Ulam spiral and Goldbach's conjecture, clock arithmetic and check digits, a Caesar cipher to crack, RSA step by step, and the HTTPS padlock and passwords.
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Infinity · paradoxes that work
Hilbert's hotel with infinitely many buses, Cantor's diagonal, Achilles and the tortoise, the Koch snowflake and Gabriel's horn, the Banach–Tarski paradox, and infinity in the world and in the computer.
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