– one that is only true in the limit; see power-law probability distributions below for details. Typically the exponent falls in the range , though not always. Examples More than a hundred power-law distributions have been identified in physics (e.g. sandpile avalanches), biology (e.g. species extinction and body mass), and the social sciences (e.g. city sizes and income). Among them are: Astronomy Kepler's third law The initial mass function of stars The differential energy spectrum of cosmic-ray nuclei The M–sigma relation Physics The Angstrom exponent in aerosol optics The frequency-dependency of acoustic attenuation in complex media The Stefan–Boltzmann law The input-voltage–output-current curves of field-effect transistors and vacuum tubes approximate a square-law relationship, a factor in "tube sound". Square–cube law (ratio of surface area to volume) A 3/2-power law can be found in the plate characteristic curves of triodes. The inverse-square laws of Newtonian gravity and electrostatics, as evidenced by the gravitational potential and Electrostatic potential, respectively. Self-organized criticality with a critical point as an attractor Model of van der Waals force Force and potential in simple harmonic motion Gamma correction relating light intensity with voltage Behaviour near second-order phase transitions involving critical exponents The safe operating area relating to maximum simultaneous current and voltage in power semiconductors. Supercritical state of matter and supercritical fluids, such as supercritical exponents of heat capacity and viscosity. The Curie–von Schweidler law in dielectric responses to step DC voltage input. The damping force over speed relation in antiseismic dampers calculus Folded solvent-exposed surface areas of centered amino acids in protein structure segments Psychology Stevens's power law of psychophysics (challenged with demonstrations that it may be logarithmic) The power law of forgetting Biology Kleiber's law relating animal metabolism to size, and allometric laws in general The two-thirds power law, relating speed to curvature in the human motor system. The Taylor's law relating mean population size and variance of populations sizes in ecology Neuronal avalanches The species richness (number of species) in clades of freshwater fishes The Harlow Knapp effect, where a subset of the kinases found in the human body compose a majority of published research The size of forest patches globally follows a power law The species–area relationship relating the number of species found in an area as a function of the size of the area Meteorology The size of rain-shower cells, energy dissipation in cyclones, and the diameters of dust devils on Earth and