Every equation is
a picture in your mind.
Feynman said that when he read an equation, he saw it happening. Read F = ma and a picture should appear: something pushed — and it accelerates. That's the whole idea behind Physica. All 400 formulas come alive as accurate, hands-on simulations, with derivations, worked examples, and the stories of the people who discovered them.
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Hand-built, physically exact — fire electrons one at a time at a double slit, build atoms from quarks, bend starlight around a black hole, set off a chain reaction. Every pixel computed from the real equation.
General Relativity: Light Bending & Curved Spacetime
Mass curves spacetime, and light follows the straightest possible path through that curved geometry — so starlight grazing the Sun bends by 1.75 arcseconds, exactly twice what Newton's gravity-on-light would give. The same curvature, turned up, gives gravitational lensing, Einstein rings, ripples in spacetime itself (gravitational waves), and at the extreme, black holes from which no path leads out.
de Broglie Wavelength
Momentum and wavelength are inversely related through Planck's constant — big things have unmeasurably tiny wavelengths.
Building Atoms from the Standard Model
Everything you've ever touched is three particles: up quarks, down quarks, and electrons. Two ups and a down make a proton (+1); one up and two downs make a neutron (0). The proton count Z picks the element, the neutron count N picks the isotope, and the electron count sets the charge. Stray too far from the stable Z–N balance and the weak force flips a quark — beta decay — to restore it.
Standard Model Interactions
Every particle reaction in nature is built from a handful of vertices — an electron emitting a photon, a quark emitting a W boson, a gluon splitting. Glue these elementary moves together and you get beta decay, annihilation, Compton scattering, pair production. The bookkeeping rules are absolute: electric charge, lepton number, and baryon number in must equal out. If a reaction conserves them all, somewhere in the universe it happens.
Kepler's Third Law
Farther orbits take longer — and not linearly: the period grows as the 3/2 power of the orbital radius.
Nuclear Chain Reaction
One neutron splits a uranium-235 nucleus, releasing ~200 MeV and ν ≈ 2.4 fresh neutrons. If, on average, more than one of those goes on to cause another fission (k > 1), the population explodes geometrically — 2, 4, 8, … 2⁸⁰ in microseconds. A reactor is the art of pinning k at exactly 1.000; a bomb is k ≈ 2 with nothing in the way.
Lorentz Force Law
Electric fields push charges; magnetic fields deflect moving charges sideways.
Tidal Force
Gravity weakens with distance, so the Moon pulls Earth's near side harder than its center, and the center harder than the far side. In Earth's frame that difference stretches the planet along the Moon line and squeezes it sideways — two ocean bulges, two high tides a day. Because the effect goes as 1/d³ (not 1/d²), the nearby Moon out-tides the enormous Sun.
Boltzmann Entropy
Entropy counts the number of microscopic ways a macroscopic state can be realized — more ways means higher entropy.
Nine domains, one library
Mechanics
50Forces, motion, energy
Electromagnetism
52Charges, fields, light
Thermodynamics
37Heat, entropy, engines
Waves & Optics
38Interference, refraction
Quantum
47Wave-particle duality
Relativity
49Spacetime, Lorentz
Modern Physics
27E=mc², photoelectric
Nuclear & Particle
29Decay, fission, quarks
Fluid Mechanics
34Bernoulli, viscosity
Mathematical Physics
37Tensors, groups, PDEs