If I damp a torsion pendulum, a force will work on it given by F = -k*v, where k is some constant and v is the velocity. My question is, how can I from this calculate the torque, which this affects the torsion pendulum with? I've tried myself, however, I'm sure there's something wrong: For a particle in the pendulem, since v = r*w, where r is the distance from axis to point in which the force works and w is the angular speed, I get: < EDIT F = -k*r*w Then I multiply both sides with r, getting the torque in this point: F*r = -k*r^2*w <=> T = -k*r^2*w, where T is the torque. For the entire pendulum the torque is then: [tex]T = \sum(-k*r^2*w)[/tex] -k and w are constant, so: [tex]T = -k*w\sum(r^2)[/tex] However, I don't get this, since the sum of the distance of all particles is either infinit or zero. Could someone explain to me what I've done wrong, or perhaps just show me, with what torque the damping really works. Thank you very much.