Thu November 10, 2011 By:

no net force doesnt mean that torque is zero-but torque is r f sin theta-if f is zero why torque is still not zero?

Expert Reply
Fri November 11, 2011
If there is a net torque, it's angular speed should change. But it appears that the angular speed is not changing (question says it's v/r, and doesn't mention that it's changing), it just turning with a constant speed. No net force doesn't mean no motion, it means no accelearion.
A torque is not separate from a force; it is impossible to exert atorque without exerting a force. Torque is a measure of how effective a given force is at
 twisting or turning something. For something rotating about a fixed axis such as the bicycle wheel, a torque can
When stopping the bicycle wheel with two equal and opposite forces, the net applied force is zero and, thus, the wheel is in translational equilibrium; but the
net torque is not zero, so it is not in rotational equilibrium. Both forces tend to give the wheel the same sign of angular acceleration; they are both making the wheel slow down. The two torques are in fact equal, with the same sign.
change the rotational motion either by making it rotate faster or by slowing it down.



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