Vibration it can be very harmful – leading to eventual failure of the system. Consequently, one of the major reasons for vibration analysis is to predict when this type of resonance may occur and then to determine what steps to take to prevent it from occurring. As the amplitude plot shows, adding damping can significantly reduce the magnitude of the vibration. Also, the magnitude can be reduced if the natural frequency can be shifted away from the forcing frequency by changing the stiffness or mass of the system. If the system cannot be changed, perhaps the forcing frequency can be shifted
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