⚛️ Physics
SI units, basic formulas, physical constants, and the history of physics.
Physical quantities and SI units
The seven SI base units, plus the most commonly used derived units and prefixes in physics.
| Quantity | Symbol | SI unit | Symbol |
|---|---|---|---|
| Length | l | metre | m |
| Mass | m | kilogram | kg |
| Time | t | second | s |
| Electric current | I | ampere | A |
| Temperature | T | kelvin | K |
| Amount of substance | n | mole | mol |
| Luminous intensity | Iₜ | candela | cd |
Derived units
| Quantity | Symbol | SI unit | Symbol |
|---|---|---|---|
| Force | F | newton | N |
| Energy / work | E / W | joule | J |
| Power | P | watt | W |
| Pressure | p | pascal | Pa |
| Frequency | f | hertz | Hz |
| Electric charge | Q | coulomb | C |
| Voltage | U | volt | V |
| Resistance | R | ohm | Ω |
| Magnetic flux | Φ | weber | Wb |
SI prefixes
| Prefix | Symbol | Factor |
|---|---|---|
| Tera | T | 10¹² |
| Giga | G | 10⁹ |
| Mega | M | 10⁶ |
| Kilo | k | 10³ |
| Centi | c | 10⁻² |
| Milli | m | 10⁻³ |
| Micro | µ | 10⁻⁶ |
| Nano | n | 10⁻⁹ |
| Pico | p | 10⁻¹² |
Basic formulas
The most commonly used formulas in mechanics, electricity, wave theory, gravitation and pressure.
Mechanics
| Name | Formula |
|---|---|
| Velocity | v = s / t |
| Acceleration | a = Δv / t |
| Newton's 2nd law | F = m · a |
| Momentum | p = m · v |
| Work | W = F · s |
| Kinetic energy | Eᶍ = ½ · m · v² |
| Potential energy | Eᶩ = m · g · h |
| Power | P = W / t |
Electricity
| Name | Formula |
|---|---|
| Ohm's law | U = R · I |
| Electric power | P = U · I |
| Electric energy | W = P · t |
Waves & light
| Name | Formula |
|---|---|
| Wave speed | v = f · λ |
| Period | T = 1 / f |
Gravitation & pressure
| Name | Formula |
|---|---|
| Newton's law of gravitation | F = G · (m₁ · m₂) / r² |
| Pressure | p = F / A |
| Density | ρ = m / V |
Physical constants
Some of the most central physical constants.
| Constant | Symbol | Value |
|---|---|---|
| Speed of light in vacuum | c | 299,792,458 m/s |
| Gravitational constant | G | 6.674 × 10⁻¹¹ N·m²/kg² |
| Planck constant | h | 6.626 × 10⁻³⁴ J·s |
| Elementary charge | e | 1.602 × 10⁻¹⁹ C |
| Avogadro constant | Nᵤ | 6.022 × 10²³ mol⁻¹ |
| Boltzmann constant | k | 1.381 × 10⁻²³ J/K |
| Gravitational acceleration (Earth) | g | 9.82 m/s² |
History of physics
A quick tour through the development of physics across more than 2000 years.
Aristotle
Aristotle describes motion and the four elements, laying the groundwork for natural philosophy, even though many of his ideas were later shown to be wrong.
Galileo and the experimental method
Galileo Galilei uses systematic experiments and the telescope to support the heliocentric model and to study falling bodies.
Newton's Principia
Isaac Newton publishes "Principia Mathematica" with his three laws of motion and the law of gravitation, which underpin classical mechanics for over 200 years.
Electromagnetism
Faraday, Ampère and Maxwell show that electricity, magnetism and light are connected, unifying them in Maxwell's equations.
Quantum physics and relativity
Planck, Einstein, Bohr and Heisenberg revolutionise physics with quantum mechanics, while Einstein's theories of relativity reshape our understanding of space, time and gravity.
Nuclear and particle physics
The discovery of the atomic nucleus's structure leads to nuclear physics and later the Standard Model of particle physics.
Modern physics
Discoveries such as the Higgs boson (2012) and gravitational waves (2015) confirm predictions from the Standard Model and general relativity.
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