Physics you can see.

Work in progress, coming soon.

The next batch, already taking shape.

Everyday maths

• 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.d = v × Δt
• 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.v = πD · (N_c/N_s) · f
• 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.A = P(1 + r/n)^nt
• 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.ΔF = D(1/mpg₁ − 1/mpg₂)
• 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.n = Σb_i·2ⁱ
• 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.P(n) = 1 − ∏(365−k)/365
• 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.A/V = 6/L
• Decibels don't add up — Drag the decibel slider and watch actual sound intensity and perceived loudness pull apart onto two very different curves.dB = 10·log₁₀(I/I₀)

Discoveries

• Why materials are not all arranged alike — Copper, brass, steel, ceramic, plastic and glass may all look solid — but their atoms organise in fundamentally different ways.
• One particle, two slits — Change a double-slit experiment and see wave fringes, individual detection events, and why making the path measurable removes the interference pattern.d sinθ = mλ
• Flush the hot air from a parked car — Open one rear window and swing the opposite front door to see why a pressure pulse clears cabin air faster than one opening alone.
• Why this window is fogging up — Set room temperature, humidity and the glass surface temperature to see exactly when invisible vapour turns into droplets.T_d = bγ/(a − γ)
• How a desert night can make ice — Change air temperature, humidity and cloud cover to see a shallow pool radiate enough heat to freeze while the air stays above 0°C.q_rad = ε_wσ(T_w⁴ − ε_skyT_a⁴)
• A little slower saves a lot of fan power — Turn one speed control and watch airflow fall linearly, pressure by the square, and ideal shaft power by the cube.P₂/P₁ = (N₂/N₁)³
• The room feels colder than the thermostat says — Drag a person around a room box and watch comfort shift with a cold window's radiant pull — even when the air temperature never moves.PMV = [0.303e^−0.036M + 0.028] × (M − L)
• You are seeing the past — Choose a planet and compare where its light began with where that planet is now.s = vd/c
• The pull between worlds — Change mass and distance to feel Newton’s inverse-square law take effect.F = Gm₁m₂/r²
• 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.n₁ sinθ₁ = n₂ sinθ₂
• Why one more passenger costs so much fuel — See why required propellant grows exponentially, not linearly, with the speed change a rocket needs.Δv = v_e·ln(R)
• 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.T = 2π√(a³/(G(M+m)))
• 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.P_loss = I²R
• 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.T = ⁴√(S(1−α)/(4σ))
• 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.r_s = 2GM/c²
• 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.P(D|+) = P(+|D)P(D)/P(+)
• 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.f(t) = (4/π)Σsin(kωt)/k
• 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.v_esc = √(2GM/r)
• 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.N = N₀e^−λt
• 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.f′ = f × v/(v∓v_s)
• Starlight has a barcode — Drag a hydrogen electron's jump to emit one exact colour, then pick a real star and see which elements' dark lines show up in its light.1/λ = R(1/2² − 1/n²)
• Orbit isn't up. It's sideways. — Fire Newton's cannonball harder and harder from a mountain and watch it go from crashing, to orbiting, to leaving Earth for good.v_circ = √(GM/r)
• Straight lines that don't stay straight — Watch a ball roll dead straight across a spinning disc and still look like it curves — then see why it's real for artillery but invisible in your bathtub.y = Ω sinφ · d²/v

Fun physics

• How water climbs — Change a liquid and an ideal glass-tube radius to see what sets capillary height and speed, then test the limits with a simple glass-gap experiment at home.h = 2γcosθ/(ρgr)
• 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.T = 2π√(L/g)
• 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.v = √(2mg/(ρAC_d))
• All the salt in the sea — Evaporate every ocean, spread the leftover salt over dry land, and see how deep the pile gets.h = m/(ρA)
• The ten-metre ceiling — However hard a pump pulls, no vacuum on Earth can lift water past one fixed, unbeatable height.h = P₀/(ρg)
• 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.T(t) = T_a + (T₀ − T_a)e^−kt
• 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.Q = 1/√((1−x²)² + (b̂x)²)
• A string you can actually hear — Change a string's length, tension, and thickness, then press play and actually hear the pitch move.f = 1/(2L) · √(T/μ)
• 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.v = √(kL²/m)
• 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.I ∝ 1/λ⁴
• Why ships float — Load cargo onto a steel hull and watch it settle lower in the water, until it finally floods and sinks.F_b = ρVg
• All animal life, by weight — Stack humans, livestock, and every wild mammal on Earth by total weight, not headcount.M = Σn·m
• 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.h_n = h₀e²ⁿ
• What is a vacuum? — Lower the pressure on one side of a liquid and see why the surrounding air pushes it across — then see why gravity keeps most of Earth's atmosphere from escaping into space.F = ΔP × A