The numbers come from tested code, not from prose
Behind the interactives sit small, self-contained libraries that do the real science and maths: orbital mechanics, molecular dynamics, the gas laws, forces and motion, reaction balancing, coordinate geometry, and more. Each one is a pure module with no interface attached, which means it can be tested directly.
There are 10 automated test suites covering those libraries, and they assert the physics itself rather than the pixels. A few real examples:
- Total energy is conserved by the molecular-dynamics integrator, and the simulated speed distribution matches the analytic Maxwell-Boltzmann curve.
- Momentum is conserved in every collision, while kinetic energy is conserved only when the collision is perfectly elastic.
- A projectile launched at 45 degrees travels farther than at any other angle, and complementary angles land at the same distance.
- Planet positions reproduce Earth's known J2000 longitude, and Kepler's third law holds across the whole solar system.
- Every chemical equation in the reactions lesson balances, and the molar masses agree with the periodic table data.
If a change ever broke one of those relationships, the tests fail and the change does not ship. That is why the readouts in a widget can be trusted as physics rather than as decoration.
Every lesson cites its sources
All 48 lessons list the references they were built from, at the bottom of the page, with links you can follow and check. The authorities we lean on most include OpenStax (Rice University), Chemistry LibreTexts, NIST, NASA and its Jet Propulsion Laboratory, the National Institutes of Health (PubChem), the National Human Genome Research Institute, and Encyclopaedia Britannica.
Reference datasets are used as published rather than retyped by hand. The 118-element data set, the planetary and lunar orbital elements, and the thermodynamic constants all come from those sources, so an element's ionisation energy or a moon's orbital period is the measured value, not an approximation someone remembered.
Simplifications are labelled, not hidden
Teaching models are simplified on purpose, and we say so on the page where it matters. The particle simulation uses relative units rather than kelvin and pascals, and says so. The orrery is built for scale and period rather than ephemeris-grade precision, and says so. The simple-machines lab reports ideal, frictionless mechanical advantage, and says so. Where a model would mislead if you took it literally, the caveat sits next to the model.
Every page shows when it was last reviewed
Each lesson carries a last reviewed date. When a lesson is corrected or extended, that date moves, so you can always see how current the page you are reading is.
Tell us when we are wrong
We would rather hear it than not. If a number looks off, a diagram misleads, or an explanation trips over a real misconception, email support@prepok.com and say which page and what looks wrong. Corrections to the science are made ahead of anything else on the roadmap, and the review date on the page moves when they land.
Free to use, free to embed
Every lesson is free, needs no account, and runs in the browser. Teachers can embed any interactive on their own site or LMS with a single line, with no ads inside the embed. More about the project and the people behind it is on the about page.