The language of understanding.

Gravity

Attraction between masses in this Newtonian model.

Orbit

A path followed under gravity.

Velocity

Rate of position change with magnitude and direction.

Acceleration

Rate of velocity change in m/s².

Specific energy

Energy per unit mass in J/kg.

Electric charge

Source of electric interactions, measured in coulombs C.

Electric field

Force per unit positive test charge in N/C.

Superposition

Calculating linear contributions separately and adding them.

Potential

Potential energy per charge; J/C=V.

Magnetic field

A field exerting q(v×B) force on moving charges.

Amplitude

Maximum displacement from equilibrium.

Frequency

Cycles per second in Hz.

Wavelength

Distance between successive equal-phase points.

Phase

Angular position within a cycle in radians.

Node

A point of zero displacement amplitude in a standing wave.

Spectrum

A signal’s frequency components and their amplitudes.

Sampling

Measuring a signal at discrete time intervals.

Momentum

Mass times velocity, a vector quantity conserved in an isolated system.

Angular momentum

For the circular point-mass model, L=mr²ω. It is conserved without external torque.

Moment of inertia

The rotational analogue of mass; I=mr² for a point mass at radius r.

Period

The elapsed time for one complete cycle of a repeating motion.

Hooke’s law

A linear spring’s restoring force is F=−kx.

Refraction

Change in wave direction when phase speed changes across an interface.

Refractive index

The ratio n=c/v of vacuum light speed to phase speed in a medium.

Critical angle

The incidence threshold for total internal reflection from higher to lower refractive index.

Focal length

Distance from a thin converging lens to the focus of incoming parallel paraxial rays.

Diffraction

Wave spreading and interference caused by a finite aperture or obstacle.

Temperature

An equilibrium quantity connected to mean molecular kinetic energy, measured in kelvin.

Diffusion coefficient

The coefficient D relating mean squared displacement to time: ⟨r²⟩=6Dt in three dimensions.

Brownian motion

Irregular tracer motion described statistically by a stochastic diffusion model.

Wavefunction

A complex probability amplitude ψ; its squared magnitude gives probability density.

Quantum number

An integer labelling an allowed state set by a quantum model and its boundaries.

Tunnelling

Nonzero quantum transmission through a finite barrier even when E is below its height.

Orbital

A stationary atomic wavefunction, not a classical path followed by an electron.

Uncertainty relation

A Gaussian minimum-uncertainty packet has ΔxΔk=1/2.

Spectral leakage

Spreading across Fourier bins when a finite observation does not contain an integer number of cycles.

Dimensionless ratio

A ratio without units, useful for comparing physically similar systems.