Physics reference data
Core physics concepts and laws.
Topic guide
What Physics covers
Physics reference data summarizes the laws and quantities that describe matter, motion, energy and waves: classical mechanics and its conservation laws, thermodynamics, electromagnetism, optics, waves and sound, and the core principles of quantum mechanics. Most entries pair a verbal statement with an equation, and the equation only makes sense with its assumptions: classical mechanics fails near the speed of light and at atomic scales, and thermodynamic laws are statistical statements about large systems. Units and the domain of validity are part of every answer.
Key ideas
- Conservation law
- A quantity that stays constant in a closed system: energy, momentum, angular momentum and charge. Many problems are solved by choosing which conservation law applies.
- Field
- A quantity defined at every point in space, such as the electric or magnetic field, that mediates forces between objects.
- Wave
- A disturbance that transfers energy without transferring matter. Wavelength, frequency, amplitude and speed are linked: speed equals frequency times wavelength.
- Entropy
- A measure of how many microscopic arrangements correspond to a macroscopic state; in isolated systems it does not decrease.
- Superposition
- Waves, and quantum states, add: the combined disturbance is the sum of the parts.
- SI units
- The metric system used in physics: meter, kilogram, second, ampere, kelvin, mole and candela, with derived units such as newton, joule and watt.
- Domain of validity
- The conditions under which an equation holds, for example speeds much less than the speed of light for Newtonian mechanics.
Common pitfalls
- Applying a formula without checking its assumptions (constant acceleration, ideal gas, small angles, non-relativistic speeds).
- Mixing units, for example grams with kilograms or Celsius with kelvin in thermodynamic formulas.
- Treating the uncertainty principle as a limit of measuring equipment; it is a property of quantum states.
- Restating the second law as 'disorder always increases' without the condition that the system is isolated.
Using it from an agent
- Give the equation, define each symbol with its SI unit, and state its domain of validity.
- For numerical answers, show units through the calculation and round to a sensible number of significant figures.
- Say when a topic is a model rather than a law; wave-particle duality and similar ideas have interpretations that physicists still debate.
Start with: Classical Mechanics: Laws of Motion and Energy · Laws of Thermodynamics
Datasets in Physics
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Classical Mechanics: Laws of Motion and Energy
Foundations of classical mechanics: Newton's laws, conservation laws (energy, momentum, angular momentum), Lagrangian and Hamiltonian mechanics, and oscillations.
13 entries -
Electromagnetism Basics
Fundamental concepts in electromagnetism.
16 entries -
Laws of Thermodynamics
The four laws of thermodynamics.
7 entries -
Optics Fundamentals
Basic concepts in the study of light.
16 entries -
Quantum Mechanics: Core Principles and Phenomena
Foundations of quantum mechanics: wave-particle duality, Schrödinger equation, Heisenberg uncertainty, quantum superposition, entanglement, and measurement problem.
7 entries -
Waves and Sound
Properties of mechanical waves and sound.
16 entries
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