# Thought experiment regarding artificial gravity (Newton's third law in space)

I was recently reading about artificial gravity and generating it in space, especially by centripetal force using Stanford Tori and Bernal sphere (only Wikipedia and these to articles, but if anyone has any more resources, I would be glad to read them, I couldn't find anything else in my search). If an electrical engine would be in a rod (well, the shape, not actually a rod) and would rotate the tori around the rod (the 0G and 1G parts of the space shuttle), since the rod has smaller mass, what would happen? Would the rod spin counter-clockwise, the tori clockwise, or both in different senses of rotation? Is this any different from how they would behave on earth (under gravity). And would it change the situation, if the initial push was generated by thrusters on the circumference of the torus/sphere ?

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Angular momentum will be conserved. This means that rod and torus will rotate in opposite directions, and that since the rod has smaller mass than the torus, it will rotate faster than the torus.

This will work the same way at the surface of the Earth, assuming that we can find a way to let the structure rotate freely (mounted on "perfect" bearings in a vacuum, for instance).

The thrust engines will also work by conserving angular momentum: the engines throw out mass in one direction of rotation, causing the structure to accelerate in the other direction of rotation.

So they would behave kind of like gears?

and since what you said is true, the rod (hollow) will also experience a much weaker artificial gravity, right?