when actually does a torque come into consideration?; In rotation motion the direction of accelaration changes but magnitude does not then why do we have

V=r  where V=linear velocity,r=radius,=angular velocity

 Dear

   First torque is not an independent quantity to define torque all you need is force and a point about which you need torque theneed of this arise when wedeal with rigid body rotation because in caserigid body rotation its not ony force but also distance of the point of application ( distance from the axis of  rotation ) decides the rate of change of angular velocity which is angular accleration have evertried to sgut the door by puuli it near the hinge you will find you are apply greater force as in caseof edge of the door

 

 

 

secondly the acceleration you aretalking about is centripetal acceleration but  is angularacceleration   which arises due ton change in    and  r is linear acceleration of a point at the circumferance centripetal acceleration exists even when omega is constant but alpha arises only when omega changes