Let’s say you’re riding one of those gravitron rides that are common at carnivals but this one is different. It’s a gravitron inside a gravitron and you’re in the inner gravitron. The outer gravitron spins clockwise and the inner gravitron along with it fast enough so that you feel 3 G’s of force. While the outer gravitron is spinning clockwise the inner gravitron begins to spin counter clockwise fast enough to simulate 3 G’s of force. Since the inner gravitron is spinning the opposite direction as the outer gravitron would you feel O G’s of force or 6 G’s of force?
Follow up question if the force is doubled. You have the outer platform spinning one direction and the inner platform spinning the opposite direction at the same speed. Relative to the earth it would look like the person riding the inner platform is standing still. Could anti gravity be simulated by tilting the ride 90° so that the rider is constantly facing the ground while feeling 6 G’s of force pushing him upward?
In: Physics
(Just gonna address the first part of your question where the two centrifuges spin in the same plane.)
For a brief moment, yeah, you could feel 0 G’s of force in a device like this. But only for a particular moment in the spin of the inner gravitron, when the directions of these two accelerations are opposite. Remember that to produce this centripetal force, you need to be spinning in a circle, and if you want to produce a specific *amount* of force, you’re constrained in choosing either the radius of the circle or the rate of spin. If they’re different radii, then, you can’t ‘sync up’ so that they’ll always be in opposite directions.
For part of the spin, the two nested centrifuges could produce force in opposite directions, and could cancel each other out, and for some part of it, they’ll produce force in the same direction, and you’ll have to add them rather than subtract them. And this is the case whether the two centrifuges spin in the same direction or opposite direction.
So, with appropriate choices for the radius and speed of the two spinning parts, you could make a gravitron-within-a-gravitron which violently jerks you back and forth between experiencing O G’s and 6 G’s. That’s about the best we can do.
If you watched someone in a nested centrifuge from above, the path they would follow belongs to one of two classes of curves called [epitrochoids](https://en.wikipedia.org/wiki/Epitrochoid) and [hypotrochoids](https://en.wikipedia.org/wiki/Hypotrochoid), which happen to be exactly the kinds of curves you can draw on your Spirograph.
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