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  Physics fundamentals — mechanics, thermodynamics, electricity, waves, optics, and modern physics concepts.


  Sources: OpenStax textbooks (CC-BY), Khan Academy, MIT OCW, NOAA, IPCC reports.
---

# Physics Fundamentals

## Classical mechanics

**Newton's Laws:**
1st: Object at rest stays at rest; object in motion stays in motion — unless acted on by external force.
2nd: F = ma (Force = mass × acceleration). Net force, not individual forces.
3rd: For every action, equal and opposite reaction.

**Kinematics (constant acceleration):**
v = v₀ + at
x = x₀ + v₀t + ½at²
v² = v₀² + 2a(x - x₀)
Free fall: a = g = 9.81 m/s² downward.

**Energy:**
Kinetic energy: KE = ½mv²
Potential energy (gravitational): PE = mgh
Conservation of energy: Total energy constant in closed system.
Work: W = F·d·cos(θ). Work-energy theorem: W_net = ΔKE.

**Momentum:** p = mv. Conservation: p_initial = p_final in closed system.
Elastic collision: KE conserved. Inelastic: KE not conserved.

## Thermodynamics

**Zeroth Law:** If A is in thermal equilibrium with B, and B with C, then A is in equilibrium with C. (Defines temperature.)
**First Law:** ΔU = Q - W. Internal energy change = heat added - work done by system.
**Second Law:** Entropy of isolated system never decreases. Heat flows spontaneously from hot to cold.
**Third Law:** Entropy approaches zero as temperature approaches absolute zero.
**Absolute zero:** 0 K = -273.15°C. Cannot be reached in practice.

## Electricity and magnetism

**Coulomb's Law:** F = k(q₁q₂)/r². Attraction or repulsion depending on sign.
**Electric field:** E = F/q. Direction of force on positive test charge.
**Ohm's Law:** V = IR. (See electrical engineering skill for circuits.)
**Faraday's Law:** Changing magnetic flux induces EMF. Foundation of electric generators and transformers.
**Maxwell's equations:** Four equations that describe all classical electromagnetism. Also predicted light as electromagnetic waves.

**Electromagnetic spectrum:**
Radio < Microwave < Infrared < **Visible light** < Ultraviolet < X-ray < Gamma ray.
All travel at c = 3×10⁸ m/s in vacuum.
E = hf = hc/λ (energy of photon).

## Waves and optics

**Wave properties:** Wavelength (λ), frequency (f), amplitude, speed. v = fλ.
**Interference:** Constructive (same phase, amplitude adds). Destructive (opposite phase, amplitude cancels).
**Doppler effect:** Observed frequency shifts with relative motion. Source approaching → higher pitch. Source receding → lower pitch. Applies to light (redshift/blueshift).
**Snell's Law:** n₁sin(θ₁) = n₂sin(θ₂). Light bends at interface between media.
Total internal reflection: If angle of incidence > critical angle, light reflects instead of refracts. Foundation of fiber optics.

## Modern physics

**Special relativity:** Speed of light constant for all observers. At relativistic speeds: time dilation, length contraction, mass increase.
E = mc²: Mass-energy equivalence.
**Quantum mechanics:** Energy is quantized. Particles have wave-like properties. Heisenberg uncertainty principle: ΔxΔp ≥ ℏ/2 — cannot simultaneously know position and momentum precisely.
**Nuclear physics:** Strong nuclear force binds protons and neutrons. Fission: heavy nuclei split, releases energy. Fusion: light nuclei combine, releases even more energy per mass.

Sources: OpenStax University Physics (CC-BY), MIT OCW 8.01/8.02, Khan Academy Physics