Question

my physics teacher said that in simple harmonic motion of simple pendulum the direction of torque acting is opposite to angular displacement now i am wondering how ?as angular displacement is either anticlockwise or clockwise and torque direction is outward or inward to the plane of paper so how their directions are opposite?please answer i am really confused thanks.

Answer 1

It is a question much easier to explain with a diagram.

On the other hand, you probably already understand that in a simple harmonic motion (SHM), the restoring force is proportional to the angular displacement, and the direction is opposite to it (for small oscilations of a pendulum).

This restoring force multiplied by the length of the pendulum creates what your teacher calls a torque. Think of using a wrench to tighten a pipe, you are applying a force perpendicular to the rotation of the pipe, so the restoring force is also perpendicular to the axis of rotation, namely the fixed end of the pendulum string.

Hope that clears up a little.