Suppose a body is rotating with uniform speed i.e. dv/dt=0(all the drags and frictions are zero) then what will be the direction of torque or will it actually exist?since the only force is acting towards the center and radius and force will make angle of 0 and hence the torque will be zero

  • $\begingroup$ If there's a torque, the body cannot be rotating with uniform speed. $\endgroup$ – Allure Jan 25 '18 at 6:19
  • $\begingroup$ @Allure that's what my doubt was!!!! that in such a case there wont be any torque?what about linear momentum? $\endgroup$ – user181463 Jan 25 '18 at 6:21
  • $\begingroup$ -1 Not clear what your "doubt" is. If you know that there is no torque, what is your difficulty? $\endgroup$ – sammy gerbil Jan 26 '18 at 5:22
  • $\begingroup$ Possible duplicate of Torque direction meaning $\endgroup$ – sammy gerbil Jan 26 '18 at 5:27

Torque is needed to speed up or slow down a spin. Here, the spinning rate is constant, so there will be no net torque. The word "net" here is extremely important. Let's say I apply $2$ $5$N forces in opposite directions. Then, there is torque, but they cancel out.

Now to angular momentum. Linear momentum $p$ is defined by $mv$, mass multiplied by velocity. Assuming the mass is non-zero, there will be momentum. One way to visualise this is to spin a heavy metal ball, using yourself at the pivot. Uponn letting go, the ball will fly. Why? Because there us momentum.

  • $\begingroup$ Sir what would the direction of torque in case the ball is object is rotating in normal situation and there is non zero drag and friction and the ball is gradually slowing down $\endgroup$ – user181463 Jan 25 '18 at 7:51
  • $\begingroup$ @user181463, the torque will be in a direction perpendicular to the plane of rotation. $\endgroup$ – QuIcKmAtHs Jan 25 '18 at 11:41

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