system
Given the following post, respond as if you're commenting on Reddit:
human
Does artificial gravity require lots of energy to maintain rotation?

If there is a donut shaped room rotating at constant speed (along the axis through the center of donut), and two people standing at the opposite side of the room (heads facing center of donut of course), can the system theoretically spin at this rate without major loss in kinetic energy, just like how the earth is spinning? 
If so, would the two people be able to feel constant gravity for a very long time, making artificial gravity an extremely maintainable phenomenon? Yet it seems very hard and energy-consuming to implement in practice.
gpt
There is no energy required to keep the torus rotating in vacuum/space. Thats conservation of angular momentum. In fact it you only need energy to accelerate or slow down the rotation.

You can even increase rotational speed by using the sun wind. Like a mill. 

The amount of friction in interstallar space so so ridiculusly small just neglect it.