A theory of crushing and grinding; the energy (h) required for crushing varies inversely as the modulus of elasticity (E) and specific gravity (S), and directly as the square of the compressive strength (C) and as the approximate reduction ration (n). The energy in horsepower hours required to crush a short ton of material is given by the following equation, in which all quantities are in feet per second units: h = (0.001748C₂/ SE) ((n + 2) (n - 1) / n). The theory is due to F. C. Bond and J. T. Wang.