A device (1,11) for use in the control of mechanical forces, the device comprising: first and second terminals for connection, in use, to components in a system for controlling mechanical forces and independently moveable; and hydraulic means (2,12) connected between the terminals and containing a liquid, the hydraulic means comprising a housing (2,12) defining a chamber for containing the liquid, the housing being attached to one of the terminals; the hydraulic means further comprising a piston (3,13) attached to the other terminal and movable within the chamber such that the movement of the piston (3,13) causes the liquid flow along at least one flow path (5,15), wherein the at least one flow path (5, 15) comprises a helical tube; characterised in that the hydraulic means, in use, stores energy in the moving liquid upon relative movement of the terminals, producing an inertial force upon changes in the relative velocity of the terminals due to the liquid flow and mass of the liquid to control the mechanical forces at the terminals to be substantially proportional to the relative acceleration between the terminals with a proportionality constant, b, greater than 50 kg, wherein the proportionality constant, b, is given by the following formula: b = m hel 1 + h / 2 πr 4 2 A 1 A 2 2 wherein m hel is the total mass of the liquid in the helical tube, h is the pitch of the helical tube, r 4 is the radius of the helical tube, A 1 is the cross-sectional area of the chamber with the chamber being a cylinder, and wherein A 1 is given by the formula, A 1 = Π (r 2 2 -r 1 2) wherein r 1 is the radius of the piston and r 2 is the inner radius of the cylinder and A 2 is the cross-sectional area of the helical tube, and wherein A 2 is given by the formula: A 2 = Π r 3 2 wherein r 3 is the inner radius of the helical tube. first and second terminals for connection, in use, to components in a system for controlling mechanical forces and independently moveable; and hydraulic means (2,12) connected between the terminals and containing a liquid, the hydraulic means comprising a housing (2,12) defining a chamber for containing the liquid, the housing being attached to one of the terminals; the hydraulic means further comprising a piston (3,13) attached to the other terminal and movable within the chamber such that the movement of the piston (3,13) causes the liquid flow along at least one flow path (5,15), wherein the at least one flow path (5, 15) comprises a helical tube; characterised in that the hydraulic means, in use, stores energy in the moving liquid upon relative movement of the terminals, producing an inertial force upon changes in the relative velocity of the terminals due to the liquid flow and mass of the liquid to control the mechanical forces at the terminals to be substantially proportional to the relative acceleration between the terminals with a proportionality constant, b, greater than 50 kg, wherein the proportionality constant, b, is given by the following formula: b = m hel 1 + h / 2 πr 4 2 A 1 A 2 2 wherein m hel is the total mass of the liquid in the helical tube, h is the pitch of the helical tube, r 4 is the radius of the helical tube, A 1 is the cross-sectional area of the chamber with the chamber being a cylinder, and wherein A 1 is given by the formula, A 1 = Π (r 2 2 -r 1 2) wherein r 1 is the radius of the piston and r 2 is the inner radius of the cylinder and A 2 is the cross-sectional area of the helical tube, and wherein A 2 is given by the formula: A 2 = Π r 3 2 wherein r 3 is the inner radius of the helical tube.