Physics you can see.

Small, honest experiments for concepts that are usually hidden inside numbers. Each page starts with one question, then lets you move the quantities yourself.

Everyday maths

Twelve pages

Quantities from an ordinary day — a storm, a car, a bicycle, a bookshelf, a pizza order, a savings account — that you can check against your own life.

01 / Geometry

Why standing up lets you see farther

Earth curves away beneath you — raise your eye height and watch the visible horizon push out from a few kilometres to thousands.

02 / Sound

How far away was that lightning?

Time the gap between the flash and the boom, multiply by the speed of sound, and measure a storm without any instrument.

03 / Motion

Why speed quadruples your stopping distance

Drag the speed slider and watch braking distance grow with the square of speed — and see reaction distance stack on top.

04 / Gearing

Same legs, different gear

Pick a chainring and a sprocket, hold your cadence steady, and watch one pedal stroke buy either speed or a hill you can actually climb.

05 / Bending

A shelf that sags

Load the middle of a plank and watch it bow — then turn the same board on its edge and see one cubed term erase almost all of it.

06 / Growth

The last decade earns more

Watch a fixed interest rate compound year after year, until the dollars added in the final decade outweigh the first three decades combined.

07 / Geometry

One big pizza, or two smaller ones?

Compare a single pizza against two smaller ones sized to true relative area — the diameter that sounds smaller usually wins.

08 / Rates

Miles per gallon is a trap

Drag two mpg values and see how much fuel each gain actually saves — the same 5 mpg jump can save six times more gas depending on where you start.

09 / Number systems

Why computers count in sixteens

Flip eight bit switches and watch a decimal number, a two-digit hex code, and sometimes a letter appear together.

10 / Probability

23 people, a coin flip

Slide the size of a room and watch the odds that two people share a birthday cross fifty-fifty at just 23.

11 / Scaling

Why the big roast takes so long

Resize a cube from a chicken breast to an elephant and watch the ratio of surface to volume decide both cooking time and body heat.

12 / Logarithms

Decibels don't add up

Drag the decibel slider and watch actual sound intensity and perceived loudness pull apart onto two very different curves.

Discoveries

Seventeen pages

The equations that changed what we knew — each one reduced to the quantities you can move yourself.

13 / Speed

Earth to the Moon, at real speed

Watch light cross the Earth–Moon gap, and magnify the tiny first part of the same journey for slower travellers.

14 / Light and distance

You are seeing the past

Choose a planet and compare where its light began with where that planet is now.

15 / Mass and energy

How much energy is in matter?

Turn an ordinary amount of mass into the energy hidden in E = mc².

16 / Gravity

The pull between worlds

Change mass and distance to feel Newton’s inverse-square law take effect.

17 / Geometry

Two sticks measure a planet

Compare shadow angles at two cities a known distance apart, the way Eratosthenes sized up the Earth around 240 BC.

18 / Optics

Why the straw looks bent

Bend a ray of light across the boundary into water or glass, then reverse it and watch the same equation cut the light off entirely.

19 / Propulsion

Why one more passenger costs so much fuel

See why required propellant grows exponentially, not linearly, with the speed change a rocket needs.

20 / Orbits

Why Mercury's year is 88 days

Slide a planet's distance from the Sun outward and watch its orbital period grow even faster than its distance.

21 / Circuits

Why the grid runs at 400,000 volts

Slide the transmission voltage up through real grid standards and watch resistive loss fall with the square of the increase.

22 / Climate

Sunlight in, heat out

Tune Earth's reflectivity and watch the balance settle on a temperature — then see how far the real 33° greenhouse gap sits above it.

23 / Relativity

Squeeze the Earth into a black hole

Pick a real mass, from a mountain to the Sun, and see how small you'd need to crush it before it became a black hole.

24 / Relativity

Moving clocks run slow

Drag a clock's speed toward light itself and watch two ticking dials — one stationary, one moving — pull apart.

25 / Probability

Why a 99%-accurate test can still be wrong

Set a disease's rarity and a test's accuracy, then watch a grid of a hundred people show how many positive results are actually real.

26 / Signals

The overshoot that refuses to leave

Add sine waves one harmonic at a time and watch a square wave emerge — with an overshoot that never quite goes away.

27 / Gravity

Why the Moon lost its atmosphere

Launch something from a real world's surface and see whether your speed clears its escape velocity or falls back down.

28 / Nuclear physics

Reading a bone's age off its isotopes

Pick a real isotope and slide elapsed time in half-lives to see how carbon dating reads a bone's remaining atoms.

29 / Waves

Why a passing siren drops in pitch

Steer a car's speed past a fixed listener and watch the pitch drop the instant it passes.

Fun physics

Fifteen pages

Oddities and quantities too big to picture, taken seriously enough to actually compute.

30 / Fluid flow

Why the straw gives up

See why a long drink straw becomes impossible to sip through while a much longer garden hose stays effortless.

31 / Oscillation

A swing keeps its own time

Pull a pendulum back further and watch its rhythm barely change — until you push past the angle where that stops being true.

32 / Falling

Falling as fast as the air allows

Change body position and mass and watch a skydiver's fixed top speed shift — then open a canopy and watch the same equation slow it to a walk.

33 / Scale

All the salt in the sea

Evaporate every ocean, spread the leftover salt over dry land, and see how deep the pile gets.

34 / Fluid pressure

The ten-metre ceiling

However hard a pump pulls, no vacuum on Earth can lift water past one fixed, unbeatable height.

35 / Heat

Milk now, or milk later?

Add cold milk right away or wait until you're ready to drink — the same physics gives a different final temperature either way.

36 / Oscillation

A small push, badly timed

Sweep a driving frequency past a system's own, and watch a small push turn into a dangerously large swing.

37 / Sound

A string you can actually hear

Change a string's length, tension, and thickness, then press play and actually hear the pitch move.

38 / Waves

Measuring light speed with chocolate

Measure the gap between two melted spots in a microwaved chocolate bar and turn it into an estimate of the speed of light.

39 / Waves

The bottom hasn't heard yet

Let go of a stretched slinky's top and watch the bottom hang motionless until the news of the drop reaches it.

40 / Optics

Why the sky is blue

Slide through the visible spectrum and see why short wavelengths paint the sky blue and long ones paint sunsets red.

41 / Fluids

Why ships float

Load cargo onto a steel hull and watch it settle lower in the water, until it finally floods and sinks.

42 / Scale

All animal life, by weight

Stack humans, livestock, and every wild mammal on Earth by total weight, not headcount.

43 / Scale

Closer to the smallest thing, or the biggest?

Slide from the Planck length to the observable universe on one logarithmic ruler and see where anything — including you — actually falls.

44 / Collisions

Count the bounces

Drop a real ball onto a real surface and watch each rebound keep the same fraction of the last one's height — then turn on a balloon drum and keep counting after your eyes give up.

What's next

More equations, waiting their turn.

The next batch is all kitchen-table science — grab something from around the house, take a real measurement, and check it against the equation.

Everyday maths

Why the spoon feels colder than the table — both are room temperature, but touch metal and wood and your hand disagreese = √(kρc)idea
How deep is the well — drop a stone, count the seconds to the splash, and back out the depthd = ½gt²idea

Fun physics

Melting ice doesn't raise the glass — float an ice cube in a full glass, mark the waterline, and watch it not moveρ_iceV_ice = ρ_waterV_dispidea

Every visual is self-contained, approximate only where stated, and designed to be played with. Each page is a single HTML file with no build step and no external dependencies — open one directly in a browser and it works.