General Science

Cars & Driving

  • noun the quality or condition of being hard


  • The resistance of a substance, material, or surface, to cutting, scratching, denting, pressure, wear, or other deformation.
  • The degree, expressed as parts per million or grains per gallon of calcium carbonate in water, to which calcium and magnesium salts are dissolved in water.


  • The relative resistance a material has to scratching, denting, bending, penetration, and/or wear, as determined by a standard test. For example, the relative resistance a material has to scratching, as indicated by the Mohs hardness scale.
  • The relative readiness with which radiation, especially X-rays, penetrates matter. The shorter the wavelength, the greater the hardness, and the more penetrating the rays.