Dashpot

A dashpot, also known as a damper[citation needed], is a mechanical device that resists motion via viscous friction.

[1] The resulting force is proportional to the velocity, but acts in the opposite direction,[2] slowing the motion and absorbing energy.

They are generally specified by stroke (amount of linear displacement) and damping coefficient (force per velocity).

Similarly, rotary dampers will tend to oppose any torque applied to them, in an amount proportional to their rotational speed.

One can distinguish two kinds of viscous rotary dashpots:[3] 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).

This permits, for example, a door to be opened quickly without added resistance, but then to close slowly using the dashpot.

Non-hydraulic rotatory dashpots may use a ratcheting gear to permit free motion in one direction.

However, the behavior of real-world dashpots is frequently non-linear, meaning that the force is proportional to the velocity raised to some exponent α, which can vary between 0.2 and 2.

Relays can be made to have a long delay by utilizing a piston filled with fluid that is allowed to escape slowly.

Large dashpots are added to bridges and buildings to protect against earthquakes and wind vibrations.