Thought experiment: Does "artificial gravity" created in a spinning spaceship last forever? We know a body in uniform linear motion will continue to move with uniform velocity unless any external force acts on it.
Similarly, a body rotating with uniform angular velocity will continue to rotate with uniform angular velocity unless any external torque acts on it.
Occupants inside a body in uniform linear motion will experience an "artificial gravity" if an external force accelerates it, but the artificial gravity will turn off the moment the external force disappears.
But in the case of a rotating body, if I understand it right, the "artifical gravity" is present (due to centrifugal force) even when no external torque is acting on it.
In that case, since the body maintains its angular velocity in the absence of any external torque, is it correct to say that
a person sitting inside a spinning spaceship will experience "artifical gravity" forever, without any intervention or additional torque required?
Assume there is just that one person sitting there, there are no other people who are walking about or moving, etc. Also, the spaceship is in empty space with no gravitational influence from any other body.
It seems that we are getting the artificial gravity "for free" without having to keep supplying an external torque, unlike in the linear case, where the artificial gravity lasted only as long as there was external force.
 A: It is all about conservation of angular momentum . A spinning body, a planet,  in space would continue spinning for ever if it were the only body in the universe. We know that gravitational forces induce tides,  in systems of planets and stars, and even though the total angular momentum is conserved individual bodies lose it.
If  the space ship is far away from gravitational bodies and such a mechansm can be ignored within lifetimes and errors, there are people in the spaceship. People will be walking and generally moving around affecting the total angular momentum with their motion due to friction with the floors. Angular momentum would escape the isolated system with the black body radiation  radiating in  preferential directions,  so unless a motor to correct for (even  if small) loss of angular momentum is included it would stop at some future time.
A: "is it correct to say that a person sitting inside a spinning spaceship will experience "artifical gravity" forever, without any intervention or additional torque required. ?"
Without any external torque, yes. But not without any intervention. The intervention needed is the centripetal force.
In any spinning body, a particle at a distance $r$ from the axis of rotation is under the influence of an external force of magnitude $mr\omega ^2$, and whose direction is towards the center of rotation. This force does not result in any torque on the particle because this force makes an angle of 0 with the line joining the particle and the axis. This force only serves to change the direction of motion of the particle to make it go in a circle, without affecting the particle's angular velocity.
Because of this force, the frame of an spinning body is an accelerated frame, which means a pseudo force is experienced in this frame.
A: Yes, the "artificial gravity" can last for a very long time (the other answers address the caveats to "forever"), but we are not getting anything for free: the person at the edge of this rotating spaceship has a force continuously applied to them, but as long as they stay in place (with respect to the ship) this force does not do any work, therefore there is no energy gain or loss.
This is due to the fact that the force is perpendicular to the displacement at any point.
This is equivalent (locally) to gravity on Earth --- gravity is continuously pulling on you if you are stationary with respect to the ground, but you are not gaining any potential energy.
On the other hand, in an accelerating spaceship you are being moved in the direction of the force, so the work is not zero.
As @mlk notes, this is all under the assumption that you are stationary in the rotating/accelerating/surface-of-the-Earth frame.
If instead, you move vertically upward in Earth's gravitational field you can gain potential energy, and analogously if you move radially inward in the rotating spaceship you can do work against the artificial gravity.
Your speed with respect to a non-rotating frame will decrease, and the rotation rate of the spaceship will increase: angular momentum is exchanged, and globally conserved.
A: Yes.
Absent external forces working on the spaceship, the sum total of angular momentum of the spaceship and all its contents will remain the same.
No action taken within the spaceship, and confined to act only on the spaceship or contents, can change this. Moving stuff inside, spinning up a wheel etc. could redistribute the angular momentum, but the sum will remain the same.
A: Yes, the system (ship + person) rotates around its center of mass forever.
Any rotating rigid body has internal stresses, that is exactly what allows it keeps being a rigid body. Otherwise its different portions would fly away following its instantaneous (tangent) velocity.
One of the internal stress of that system is the radial compression inside the person's body. On the other hand, there are tensile stresses in the structural columns that join the periphery to the center.
That is a difference compared to "natural" gravity, where the buidings columns and all bodies are under vertical compression.
