Scientific Ontology

Physics through the people who shaped it. Scroll the timeline; click any quantity to drill down.

1635
Robert Hooke
1635–1703
English polymath who formulated the law of elasticity relating force and extension.
Equations
- Hooke's Law $F = -k x$
$F$ Force $k$ Spring Constant $l$ Length
1643
Isaac Newton
1643–1727
Laid the foundations of classical mechanics with his laws of motion and universal gravitation.
Equations
- Newton's Second Law $\vec{F} = m\vec{a}$
- Linear Momentum $\vec{p} = m\vec{v}$
- Newton's Law of Gravitation $F = G\dfrac{m_1 m_2}{r^2}$
- Gravitational Field (radial) $g = \dfrac{GM}{r^2}$
- Gravitational Potential $V = -\dfrac{GM}{r}$
- Centripetal Force $F = \dfrac{mv^2}{r} = mr\omega^2$
- SHM Period (simple pendulum) $T = 2\pi\sqrt{\dfrac{l}{g}}$
$F$ Force $m$ Mass $a$ Acceleration $p$ Momentum $v$ Velocity $l$ Length $G$ Gravitational Constant $g$ Standard Gravity $V$ Gravitational Potential $t$ Time
1731
Henry Cavendish
1731–1810
Measured the gravitational constant G with a torsion balance experiment.
Equations
- Newton's Law of Gravitation $F = G\dfrac{m_1 m_2}{r^2}$
- Gravitational Field (radial) $g = \dfrac{GM}{r^2}$
$F$ Force $m$ Mass $l$ Length $G$ Gravitational Constant $g$ Standard Gravity
1736
Charles-Augustin de Coulomb
1736–1806
Quantified the electrostatic force between charges, giving his name to the unit of charge.
Equations
- Coulomb's Law $F = \dfrac{1}{4\pi\varepsilon_0}\dfrac{q_1 q_2}{r^2}$
$F$ Force $q$ Electric Charge $\varepsilon_0$ Vacuum Permittivity $l$ Length
1736
James Watt
1736–1819
Improved the steam engine; the SI unit of power is named in his honour.
Equations
- Power $P = \dfrac{W}{t}$
$P$ Power $W$ Work $t$ Time
1773
Thomas Young
1773–1829
Demonstrated light's wave nature and defined the elastic modulus; pioneered interference and diffraction.
Equations
- Young Modulus $E = \dfrac{\sigma}{\varepsilon}$
- Tensile Stress $\sigma = \dfrac{F}{A}$
- Tensile Strain $\varepsilon = \dfrac{\Delta x}{x}$
- Diffraction Grating $n\lambda = d\sin\theta$
$E$ Young Modulus $\sigma$ Stress $\varepsilon$ Strain $F$ Force $A$ Area $l$ Length $\lambda$ Wavelength
1775
André-Marie Ampère
1775–1836
Founded electrodynamics; the SI unit of current bears his name.
Equations
- Magnetic Force on a Wire $F = BIl\sin\theta$
$I$ Electric Current $F$ Force $B$ Magnetic Field $l$ Length
1776
Amedeo Avogadro
1776–1856
Hypothesised equal volumes of gases contain equal numbers of molecules; the mole is named after him.
Equations
- Ideal Gas Law $p V = n R T$
$N_A$ Avogadro Constant $p$ Pressure $V$ Volume $n$ Amount of Substance $R$ Molar Gas Constant $T$ Temperature
1789
Georg Ohm
1789–1854
Discovered the proportionality between voltage and current in a conductor.
Equations
- Ohm's Law $V = I R$
$V$ Voltage $I$ Electric Current $R$ Resistance
1791
Michael Faraday
1791–1867
Pioneer of electromagnetism and electrochemistry; discovered electromagnetic induction.
Equations
- Capacitance $C = \dfrac{Q}{V}$
- Faraday's Law of Induction $\varepsilon = -\dfrac{d\Phi}{dt}$
- Magnetic Flux $\Phi = B A \cos\theta$
$C$ Capacitance $q$ Electric Charge $V$ Voltage $\Phi$ Magnetic Flux $t$ Time $B$ Magnetic Field $A$ Area
1796
Sadi Carnot
1796–1832
Founder of thermodynamics, who analysed the efficiency of heat engines.
Equations
- First Law of Thermodynamics $\Delta U = Q - W$
- Entropy Change $\Delta S = \dfrac{Q}{T}$
$E$ Energy $Q$ Heat $W$ Work $S$ Entropy $T$ Temperature
1818
James Prescott Joule
1818–1889
Established the mechanical equivalent of heat, unifying work and energy.
Equations
- Kinetic Energy $E_k = \tfrac{1}{2} m v^2$
- Work Done by a Force $W = F d \cos\theta$
- Electrical Power $P = V I$
- First Law of Thermodynamics $\Delta U = Q - W$
- Heat Transfer $Q = C \, \Delta T$
$E$ Energy $m$ Mass $v$ Velocity $W$ Work $F$ Force $l$ Length $P$ Power $V$ Voltage $I$ Electric Current $Q$ Heat $C$ Heat Capacity $T$ Temperature
1831
James Clerk Maxwell
1831–1879
Unified electricity, magnetism and light into a single electromagnetic theory.
Equations
- Faraday's Law of Induction $\varepsilon = -\dfrac{d\Phi}{dt}$
$E$ Electric Field $B$ Magnetic Field $V$ Voltage $\Phi$ Magnetic Flux $t$ Time
1835
Josef Stefan
1835–1893
Discovered the T⁴ law of thermal radiation later explained by Boltzmann.
Equations
- Stefan–Boltzmann Law $L = \sigma A T^4$
$\sigma$ Stefan–Boltzmann Constant $P$ Power $A$ Area $T$ Temperature
1844
Ludwig Boltzmann
1844–1906
Founder of statistical mechanics, linking entropy to microscopic states.
Equations
- Ideal Gas Law $p V = n R T$
- Ideal Gas Law (Boltzmann form) $pV = Nk_BT$
- Entropy Change $\Delta S = \dfrac{Q}{T}$
- Boltzmann's Entropy Formula $S = k_B \ln W$
- Molecular Kinetic Energy $\tfrac{1}{2}m\langle c^2\rangle = \tfrac{3}{2}k_BT$
- Stefan–Boltzmann Law $L = \sigma A T^4$
$p$ Pressure $V$ Volume $n$ Amount of Substance $R$ Molar Gas Constant $T$ Temperature $k_B$ Boltzmann Constant $S$ Entropy $Q$ Heat $m$ Mass $P$ Power $\sigma$ Stefan–Boltzmann Constant $A$ Area
1853
Hendrik Lorentz
1853–1928
Described the force on charges in fields and the transformations underpinning relativity.
Equations
- Lorentz Force $\vec{F} = q(\vec{E} + \vec{v} \times \vec{B})$
- Lorentz Factor $\gamma = \dfrac{1}{\sqrt{1 - v^2/c^2}}$
$F$ Force $q$ Electric Charge $E$ Electric Field $v$ Velocity $B$ Magnetic Field $\gamma$ Lorentz Factor
1856
Nikola Tesla
1856–1943
Inventor and engineer of alternating-current systems; the unit of magnetic field bears his name.
$B$ Magnetic Field $V$ Voltage $I$ Electric Current
1858
Max Planck
1858–1947
Originated quantum theory by proposing that energy is emitted in discrete quanta.
Equations
- Planck–Einstein Relation $E = h f$
$h$ Planck Constant $E$ Energy $f$ Frequency
1864
Wilhelm Wien
1864–1928
Formulated Wien's displacement law for black-body radiation spectra.
Equations
- Wien's Displacement Law $\lambda_{\max} T = b$
$b$ Wien Constant $\lambda$ Wavelength $T$ Temperature
1868
Robert Millikan
1868–1953
Measured the elementary charge e with the oil-drop experiment.
Equations
- Photoelectric Effect $E_k = h f - \phi$
$e$ Elementary Charge $E$ Energy $h$ Planck Constant $f$ Frequency
1871
Ernest Rutherford
1871–1937
Discovered the nucleus and pioneered the model of radioactive decay.
Equations
- Radioactive Decay $N = N_0 e^{-\lambda t}$
- Activity $A = \lambda N$
- Half-life and Decay Constant $\lambda = \dfrac{\ln 2}{t_{1/2}}$
$n$ Amount of Substance $\lambda$ Decay Constant $t$ Time $A$ Activity $t_{1/2}$ Half-life
1879
Albert Einstein
1879–1955
Revolutionised physics with relativity and the quantum explanation of the photoelectric effect.
Equations
- Planck–Einstein Relation $E = h f$
- Photoelectric Effect $E_k = h f - \phi$
- Mass–Energy Equivalence $E = m c^2$
- Lorentz Factor $\gamma = \dfrac{1}{\sqrt{1 - v^2/c^2}}$
$E$ Energy $h$ Planck Constant $f$ Frequency $m$ Mass $c$ Speed of Light $\gamma$ Lorentz Factor $v$ Velocity
1889
Edwin Hubble
1889–1953
Showed galaxies recede with velocity proportional to distance, evidence for cosmic expansion.
Equations
- Hubble's Law $v = H_0 d$
$H_0$ Hubble Constant $v$ Velocity $l$ Length
1892
Louis de Broglie
1892–1987
Proposed that all matter exhibits wave-like behaviour, founding wave mechanics.
Equations
- de Broglie Wavelength $\lambda = \dfrac{h}{p}$
$\lambda$ Wavelength $h$ Planck Constant $p$ Momentum

Physics Ontology

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