Mechanics of gelation distinction between a sol (solution) and a gel therefore appears to be understood in a manner analogous to the practical distinction between the elastic and plastic deformation ranges of a metal. The distinction lies in the ability to respond to an applied shear force via macroscopic viscous flow. In a dynamic sense, the response of a gel to an alternating force (oscillation or vibration) will depend upon the period or frequency of vibration. As indicated here, even most simple liquids will exhibit some elastic response at shear rates or frequencies exceeding 5 x 10 cycles per second. Experiments on such
Number density the objects in the volume "V" can be expressed as Similar expressions are valid for electric charge or any other extensive quantity associated with countable objects. For example, replacing "m" with "q" (total charge) and "m" with "q" (charge of each object) in the above equation will lead to a correct expression for charge. The number density of solute molecules in a solvent is sometimes called concentration, although usually concentration is expressed as a number of moles per unit volume (and thus called molar concentration). For any substance, the number density can be expressed in terms of its amount concentration