Playground ·
A harmonograph drawing machine
Four decaying pendulums steer a pen; frequencies near simple ratios draw the spirograph-like curves Victorian harmonographs were famous for.
Physics
Mechanics, electricity, waves, and the physics behind the builds.
Exploration ·
How a brushless motor spins
From magnets and coils to a quadcopter in the air: how a brushless motor is wound, how an ESC switches it in six steps, how it finds the rotor without sensors, what field-oriented control does better, and what happens when you bolt four of them to a frame — with the simulators running alongside.
Exploration ·
How a jet engine makes thrust
Follow a parcel of air through a jet engine — squeezed, burned, expanded, thrown out of the back — with the cycle worked out live at every step, then see why airliner fans keep growing and why a car's turbocharger is a little gas turbine.
Tool ·
Jet engines and gas turbines
How jet engines work and what their numbers mean: an animated cutaway of turbojet, turbofan, turboprop, turboshaft, ramjet and afterburning engines with numbered stations; ideal and real Brayton cycle analysis at any Mach and altitude — thrust, TSFC, efficiencies, T–s and P–v diagrams and trade studies; compressor stages, draggable velocity triangles and a compressor map with surge margin; approximate figures for real engine families; and fuel, run time and start-up for model turbojets.
Playground ·
N-body: a small solar system, timed
The same five-body gravity simulation in fifteen languages, each timing itself — a hands-on look at how much the runtime matters when the program is all floating-point arithmetic in a tight loop.
Tool ·
Marble tilt
Roll a steel marble through a maze on a tilting 3D board — holes, railed and narrow bridges, moving platforms, bumpers and checkpoints — by tilting your phone, dragging, or with keys or a gamepad. Twelve designed levels, endless levels from a seed, and best times.
Tool ·
Earthquakes, live
Earthquakes from the USGS live feeds (past hour to past 30 days) or any date range from its catalogue, on a world map with plate boundaries — sized by magnitude, coloured by depth or age — with a filterable list, details (PAGER alert, felt reports, tsunami flag, ShakeMap), distance from you and when the P and S waves reach you, a Gutenberg–Richter plot with the b-value, and what each step of magnitude means in energy.
Tool ·
Eclipses and meteor showers
Every solar and lunar eclipse from 2020 to 2050 with its times and how much you'll see from your place — contacts, magnitude, obscuration, the path of totality on a world map — and the meteor showers of the IMO list, with the rate you can expect tonight after the radiant's height, your sky and the moon.
Tool ·
Observing planner
What's worth looking at tonight: the Messier and Caldwell objects and some showpiece stars ranked for your place, sky and telescope through the dark hours, each with an altitude chart; the night's cloud, transparency and dew forecast; a saved observing list, a session log you can download, and the Messier marathon's best night and running order.
Tool ·
Phone seismograph
Your phone's accelerometer as a seismograph: a live three-axis trace with gravity and tilt filtered out, a helicorder (drum) view, an STA/LTA trigger with an event log, peak ground acceleration in g with the approximate Modified Mercalli intensity, a spectrum to see what is shaking (footsteps, a washing machine), and recordings saved as CSV or WAV. A demo mode makes synthetic earthquakes on a desktop.
Tool ·
Planet details
The planets in your eyepiece, drawn to scale at your magnification and flipped the way your telescope shows them: Jupiter's four big moons and their transits, shadows, eclipses and occultations, and when the Great Red Spot crosses; Saturn's ring tilt and its moons; Mars's central meridian and markings; Venus's and Mercury's phases.
Tool ·
Planet events and alignments
Conjunctions of planets with each other, the Moon and bright stars, planet "parades", oppositions, greatest elongations, stations and retrograde loops, Mars's closest approach and lunar occultations — for the next year or twenty, filtered to what you can actually see from your place, each with a picture of the sky at the best moment and an .ics file for your calendar.
Tool ·
Skew-T sounding
A Skew-T log-P diagram for any place from Open-Meteo's forecast, or for a radiosonde sounding pasted from the University of Wyoming — temperature and dewpoint, dry and moist adiabats, mixing-ratio lines, wind barbs, a surface, mixed-layer or most-unstable parcel with CAPE and CIN shaded, LCL, LFC and EL, lifted index, precipitable water, freezing level, shear, storm motion and helicity, a hodograph, and a plain-English reading.
Tool ·
Sky darkness
Convert between the Bortle class, sky brightness in mag/arcsec² (an SQM reading), naked-eye limiting magnitude and how much brighter than natural your sky is; see what each class shows and a simulated star field at that darkness; and estimate tonight's limiting magnitude by altitude with the Moon up.
Tool ·
Sky tonight
A star chart for your place and time — the whole sky as a dome or a zoomable view, with stars to magnitude 6.5, constellations, the Milky Way, Messier objects, the planets and the Moon's phase; a time slider, search, rise/transit/set for anything you tap, a red night mode, and a mode that shows what your phone is pointing at.
Tool ·
Telescope mount
Polar alignment (where Polaris or σ Octantis sits on your polar-scope reticle right now, and drift alignment), setting circles (RA/Dec to altitude and azimuth and back, hour angle, sidereal time), and a GoTo controller over Web Serial for Celestron NexStar, Sky-Watcher SynScan and Meade LX200 mounts — connect, read where it points, slew, sync, nudge and stop. It refuses to slew near the Sun.
Tool ·
Heat loss and HVAC sizing
A room-by-room heat-loss and cooling-load estimate in the style of Manual J (not Manual J): U- or R-values and areas, air leakage, design temperatures for a few US cities with sources, window solar gain from the sun's position, and heat-pump sizing with the balance point — in imperial or metric.
Tool ·
Ocean lab
Predict tides from NOAA harmonic constituents and check them against NOAA's own predictions; solve the wave dispersion relation, grow wind waves, shoal and break them; compute TEOS-10 seawater properties with a T–S diagram and CTD profiles; work out Coriolis, Ekman and geostrophic currents; and plot NDBC buoy observations.
Tool ·
Beams, columns and trusses
Beam solver for simply supported, cantilever, propped, fixed and overhanging beams with point, uniform, triangular and moment loads — shear, moment, slope and deflection diagrams, stresses from a section-property calculator, steel, aluminium, wood and 3D-printed materials — plus Euler and Johnson column buckling and a drawable 2-D truss solver with tension, compression and member buckling.
Tool ·
Lasers and fibre optics
Gaussian beams (waist, Rayleigh range, divergence, w(z), R(z), Gouy phase, M²), focusing to a spot and beam expanders, ABCD q-parameter propagation through a train of lenses with an animated full-screen envelope plot, two-mirror cavity stability on the g₁g₂ diagram, fibre NA, V number, modes, cutoff and Marcuse mode field diameter, a dB link budget, modal and chromatic dispersion, approximate laser-safety MPE and NOHD, and photon arithmetic.
Tool ·
Lens design bench
A sequential lens design bench: build a prescription of spherical and conic surfaces in N-BK7, N-SF11, F2, N-SK16, fused silica, CaF₂ and plastics (Sellmeier data), trace paraxial and real rays, get the cardinal points, Seidel aberrations and longitudinal colour, spot diagrams, ray fans and an MTF estimate, bend a singlet, design an achromatic doublet, and export the prescription as CSV or JSON — with a full-screen layout.
Tool ·
Linkages and mechanisms
Mechanisms you can play with — an animated four-bar linkage with the Grashof check, its type, the coupler curve and the transmission angle; slider-cranks with stroke and quick return; disc cams with uniform, harmonic, cycloidal and 3-4-5 motion, pressure angle and undercut check; a 2- or 3-link robot arm you drag by the hand, with both inverse-kinematics solutions; and differential-drive kinematics and odometry for small robots.
Tool ·
Mode S and ADS-B decoder
Decode 1090 MHz Mode S and ADS-B messages field by field — CRC and parity, callsign, altitude, CPR positions with the maths shown, velocity, Gillham codes and Comm-B — from pasted hex, AVR or Beast frames, or live from your receiver over a WebSocket.
Tool ·
Model rocketry
Simulate a model rocket's flight from real motor thrust curves — altitude, speed and acceleration, apogee, the right ejection delay, launch-rod speed and descent under the parachute — check its stability with the Barrowman centre of pressure and a side-view drawing, size the parachute, and look up motor classes and the NAR/Tripoli safety codes.
Tool ·
Polarization
Polarised light, interactively: the polarisation ellipse from a Jones vector, an optical train of polarizers, waveplates and rotators you drag and turn (Jones calculus), Malus's law and the three-polarizer paradox, Stokes parameters on a draggable 3-D Poincaré sphere, the Fresnel equations with Brewster's angle and total internal reflection, calcite's double image, waveplate thickness, computed interference colours with a Michel-Lévy chart, photoelastic stress fringes, and how sunglasses, LCD pixels and 3-D glasses work.
Tool ·
Sensor data logger
Log a sensor for a science project from an Arduino, ESP32, Pico or micro:bit over USB (Web Serial) or Bluetooth, or from a simulated source: CSV, name:value, JSON and Serial Plotter lines plotted live with zoom and scroll, markers, per-channel statistics, units and calibration, the sample rate, recordings saved in your browser, CSV/JSON export, and example programs to copy.
Tool ·
Telescopes and optics
Telescope and eyepiece arithmetic (magnification, focal ratio, exit pupil, true field, useful power, Dawes and Rayleigh limits, limiting magnitude, Barlows and reducers), a camera on a telescope (arcseconds per pixel and sampling), binoculars, an interactive ray-tracing bench where you drag lenses and mirrors and watch images form, the lensmaker's equation and Snell's law with total internal reflection.
Tool ·
Wave optics lab
An interactive wave-optics lab: Young's slits and gratings, thin-film colours of soap bubbles and coatings computed spectrally (transfer-matrix method, CIE 1931 colour), Michelson and Fabry–Pérot interferometers, Newton's rings, the slit and Airy patterns with the Rayleigh criterion, any aperture's diffraction pattern by 2-D FFT (draw your own), Fresnel diffraction with the Cornu spiral, a grating spectrometer, and a ripple tank simulation.
Tool ·
CT and MRI lab
CT reconstruction from scratch (projections, sinograms, Poisson noise, back-projection, FBP and SART), Hounsfield units with window/level, k-space masking, MRI spin-echo contrast, and how a segmentation threshold moves a measured dimension.
Tool ·
Diffusion, dialysis and clearance
Diffusion time t ≈ x²/2D and surface-to-volume 3/r; fit a diffusion coefficient from your own dye-in-agar measurements; dialyser clearance and Kt/V; a week of kidney filtration against haemodialysis; and an animated co-current against counter-current exchanger. Educational simulation only.
Tool ·
Heart, vessels and oxygen
Cardiac output, ejection fraction, MAP and pulse pressure; ΔP = Q × R for the systemic and pulmonary circuits with a pressure cascade; Poiseuille's r⁴ for a vessel, a stenosis or a strap; Dalton, Henry and cylinder arithmetic; and the oxygen–haemoglobin dissociation curve with temperature, CO₂ and pH shifts. Educational simulation only.
Tool ·
Test lung and breathing mechanics
A simulated test lung: pressure, flow and volume waveforms from the equation of motion in volume and pressure control, time constants and breath stacking, a lung-volumes spirogram, dead space, airway radius to the fourth power, and Laplace's law. Educational simulation only.
Tool ·
Ultrasound, Doppler and dose numbers
Pulse-echo depth, wavelength, depth limit and frame rate; reflection at impedance boundaries; the Doppler shift and how an angle error moves the velocity; ultrasonic ranging in air; effective dose against natural background; Beer–Lambert, inverse square, and √N counting noise.
Tool ·
Fluid flow and pipe pressure drop
Reynolds number and Darcy–Weisbach pressure drop with Colebrook, Swamee–Jain, or Haaland friction factors and fitting losses; Hagen–Poiseuille laminar flow with an r⁴ sensitivity plot; pipe sizing from flow and velocity; Bernoulli solver; hydrostatic pressure and buoyancy; pump power and orifice flow — with unit-aware inputs.
Tool ·
Orbital mechanics
An n-body gravity simulator with presets (Sun–Earth–Moon, inner planets, the figure-eight three-body orbit, a binary star, a Jupiter Trojan), plus Hohmann transfer, Kepler's-law, escape-velocity, and orbital-element calculators.
Tool ·
Physics calculators
Physical constants and calculators for kinematics, projectiles with air resistance, oscillations, forces on an incline, collisions, waves and sound, lenses and refraction, the eye in dioptres (far point, accommodation by age, reading add), heat, gases, and orbits.
Tool ·
Room acoustics and sound
Decibel addition and background correction, inverse-square distance loss, room modes with a chart, RT60 by Sabine and Eyring from a materials table, speed of sound and wavelength, note ↔ frequency with adjustable A4, and a tone, noise, and sweep generator.
Tool ·
Spectrum analyser
Generate, load, or record a signal and analyse it: waveform, FFT spectrum with window functions and averaging, peak detection, an STFT spectrogram, and THD / THD+N / SINAD for a test tone — plus synthetic ECG, EMG, EEG and PPG with mains hum, baseline wander and noise, and a signal-averaging demo.
Tool ·
Unit converter
Convert between hundreds of units — length to radiation dose — or type a query like “3.5 ft·lbf to N·m” and let dimensional analysis do the rest.