Question

I'm taking a phycics course & I'm confused regarding the difference of Net Force & Net Torque.

Is it possible to have a system where the net force is zero, but the net torque is not zero???

And vice versa, is it possible to have a system where the net torque is zero, but the net force is not zero???

And is it possible to have a system where both Net Force & Net Torque are zero???

Can you give one example for each, thank you.

Answer 1

Net force refers to translational motion and net torque refers to rotational motion.

Yes It is possible to have net force zero and net torque as non zero. Example supporting this fact is opening the cap of a bottle and twisting it. To open the cap,We apply an equal and opposite forces on the two fingers/finger and thumb placed at two opposite sides of the cap to open it.hence the net force is zero. But Net torque is non zero as the cap rotates.

It is possible to have net torque as zero but net force non zero. Example is similar to above. In case if we apply an unequal forces on the opposite sides,net force will have a certain value but the net torque will be zero as the cap will not rotate due to that value of net force.

Yes It is possible to have net torque as zer as well as net force as zero. Example is a rod is rotating at a constant angular velocity that is it is in rotational equilibrium. The net torque is zero in this case and net force is also zero.