<P> A dashpot is a mechanical device, a damper which resists motion via viscous friction . The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy . It is commonly used in conjunction with a spring (which acts to resist displacement). The process and instrumentation diagram (P&ID) symbol for a dashpot is . </P> <P> Two common types of dashpots exist - linear and rotary . Linear dashpots are generally specified by stroke (amount of linear displacement) and damping coefficient (force per velocity). Rotary dashpots will have damping coefficients in torque per angular velocity . </P> <P> A less common type of dashpot is an eddy current damper, which uses a large magnet inside a tube constructed of a non-magnetic but conducting material (such as aluminium or copper). Like a common viscous damper, the eddy current damper produces a resistive force proportional to velocity . </P> <P> Dashpots frequently use a one - way mechanical bypass to permit fast unrestricted motion in one direction and slow motion using the dashpot in the opposite direction . This permits, for example, a door to be opened quickly without added resistance, but then to close slowly using the dashpot . For hydraulic dashpots this unrestricted motion is accomplished using a one - way check - valve that allows fluid to bypass the dashpot fluid constriction . Non-hydraulic dashpots may use a ratcheting gear to permit free motion in one direction . </P>

How dashpot and string were released in a car