# Restoring Torque in a physical pendulum?

1. Feb 10, 2008

### kthouz

I know that in the simple pendulum there is a rextoring force created by the gravity. My question now is, when we take the case of the physical (real) pendulum there is an other stuff which come in "the restorung torque" how is this created. What is infact its axis of rotion?

2. Feb 10, 2008

### Staff: Mentor

I'm not sure I understand your question. Gravity provides the restoring force in a physical pendulum just like it does in a simple pendulum. (Gravity acts through the center of mass in both cases.)

3. Feb 10, 2008

### rohanprabhu

All motion can be interpreted as rotation along a particular axis [this motion, however needs to occur in an infinitesimally small period of time dt].

So, when you mean that gravity provides the restoring force, well.. it is also providing a restoring torque. It just depends on which way you see it. Torque after all is the lever arm product of force.

In a real pendulum, we have three extra differences: The viscous force of air [air friction], friction in apparatus and the non-applicability of $\sin{(\theta)} \approx \theta$

also.. it'd be better if you could clarify your question.