Mechanical Equilibrium: Rotating w/No Net Torque

[broegger]

is an object rotating with no net torque present (such as a sphere spinning about an axis of symmetry) said to be in mechanical equilibrium??

 

[Doc Al]

Originally posted by broegger
is an object rotating with no net torque present (such as a sphere spinning about an axis of symmetry) said to be in mechanical equilibrium??

No, since there could still be a net force acting on the object.

 

[broegger]

my physics book implicitly states that if an object is rotating it is not in mechanical equlibrium - even though there is no net torque and it isn't moving through space (no net force)... but if the same object is moving through space with constant velocity (no net force) without rotating (no net torque) it IS in equilibrium - this is confusing, because to me these two situations are equivalent

 

[yxgao]

For a system to be in mechanical equilibrium, the net torque and the net force must be zero.

So assuming these are true, would a sphere spinning about an axis of symmetry be in equilibrium? According to the textbook, no?