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Learning path · 18 parts

Motion, Space & Quanta

Start with a swinging weight, bend time with relativity, and end where classical physics breaks down entirely.

About 3 hours of reading · 36 widgets

Start with The Pendulum
  1. Physics9 min

    Part 1: The Pendulum

    Why a pendulum keeps perfect time at small angles — and breaks down at large ones.

  2. Physics10 min

    Part 2: Resonance and Standing Waves

    Why timing beats strength in every oscillating system — from a playground swing to a radio tuner, an MRI scanner, and the strings of a violin.

  3. Physics10 min

    Part 3: Turbulence and the Reynolds Number

    Why candle smoke climbs smoothly and then shatters, how a single number predicts the switch, and why a bacterium swims through water as if it were honey.

  4. Physics10 min

    Part 4: Buoyancy: Why Steel Ships Float

    Why steel ships float while steel bolts sink: buoyancy comes from the weight of displaced fluid, and floating depends on average density, not on being heavy or light.

  5. Physics10 min

    Part 5: Momentum: The Quantity Collisions Conserve

    Why total momentum is always conserved in a collision, how it differs from kinetic energy, and why stretching a collision's time protects you from its force.

  6. Physics10 min

    Part 6: Angular Momentum: Why Skaters Spin Faster

    How conservation of angular momentum makes a skater spin faster when she pulls her arms in, and why a spinning gyroscope precesses instead of toppling under gravity.

  7. Physics10 min

    Part 7: Kepler's Laws of Planetary Motion

    How Kepler's stubborn refusal to ignore a tiny discrepancy in Mars's orbit produced three laws that Newton later derived from a single inverse-square force.

  8. Physics10 min

    Part 8: The Doppler Effect

    Motion crowds the waves in front of a source and stretches the ones behind. That single geometric fact explains sirens, sonic booms, weather radar, and the expanding universe.

  9. Physics10 min

    Part 9: Entropy and the Second Law

    Gas released in a corner of a box fills the box and never gathers back — not because a force forbids it, but because overwhelmingly more microstates look spread out than gathered.

  10. Physics9 min

    Part 10: Time Dilation

    How Einstein's special relativity predicts that time passes differently for observers in relative motion.

  11. Physics10 min

    Part 11: General Relativity: Gravity as Curved Spacetime

    Einstein's 1915 theory recasts gravity as the curvature of spacetime: mass-energy bends geometry, objects follow geodesics, and clocks, light, and GPS all obey.

  12. Physics9 min

    Part 12: Electric Circuits and Ohm's Law

    How current, voltage, and resistance fit together in $V = IR$ — and why charge is never used up, only energy is.

  13. Physics10 min

    Part 13: Magnetism: Moving Charges and Aligned Spins

    Magnetism is not a force separate from electricity — it comes from moving charges and aligned electron spins, forms only closed-loop dipoles, and grips only a few metals.

  14. Physics10 min

    Part 14: Maxwell's Equations and the Nature of Light

    Maxwell combined everything known about electricity and magnetism, found a self-sustaining wave hiding in the algebra, and computed its speed from two bench-top constants. The answer was the speed of light.

  15. Physics10 min

    Part 15: Optics: How Light Bends and Focuses

    Light bends when its speed changes crossing a boundary — that is refraction — and lenses harness the same effect to focus rays and form real or virtual images.

  16. Physics11 min

    Part 16: Wave-Particle Duality

    Fire electrons one at a time through two slits. What you find will change how you think about reality.

  17. Physics10 min

    Part 17: Nuclear Fission and Fusion

    The energy in nuclear reactions comes from mass literally disappearing — and one curve explains why fission and fusion both liberate it.

  18. Physics10 min

    Part 18: Superconductivity

    Cool certain metals below a critical temperature and their resistance vanishes entirely. The reason involves electrons pairing up and condensing into a single quantum state.