# Can the centripetal force be inverted? [closed]

Using the centripetal force to create artificial gravity has been proposed for space exploration. From our perspective, the force is an outward force, pushing objects away. Could it be inverted to attract them instead?

Could we, instead of having a spacecraft, or a "dish," rotate to create the force that would push the travelers to the inside of the hull - could we instead have a cluster of dishes rotating in such a manner that the travelers are pressed to the outside of a sphere?

Or, could we construct an artificial mini-planet with a gravity exceeding by far the gravity of a natural celestial body with the same mass?

Close to a black hole, but still outside the event horizon, orbiting arbitrarily fast, wouldn't result in a circular orbit, but in a trajectory towards the black hole. In this extreme scenario, centrifugal force could be interpreted as attractive.

In more usual settings, centrifugal forces point outward. Since the centrifugal force (in usual settings) $m \omega^2r$ is proportional to square of the angular velocity $\omega$, you would need an imgaginary angular velocity, or alternatively a negative mass to get an inward pointing centrifugal force.

I'm not aware of a physical realization of imaginary angular velocities, at least not for circular orbits, although this paper introduces imaginary velocities for hyperbolic orbits. This may be derived from imaginary circular angles. Negative masses aren't entirely impossible, but those potentially feasible are too tiny to be of any practical value in your sense.

• I was thinking more along the lines of actual, not imaginary, inertia. Since according to relativity gravity and inertia are one and the same, and we do know how to invert inertia in some cases (even though the waste motion in such processes is greater than useful motion), I thought that maybe something could be constructed that would ... hmm ... Today's plan is to create gravity for space travel by making some sort of "dish" rotate, creating a centrifugal force on the inside rather than on the outside. Well. This is probably just another perpetuum mobile idea. Thank you for answering. Dec 4, 2015 at 2:58
• @Ricky Sounds like you need to edit your question. It already attracted a downvote.
– user1569
Dec 4, 2015 at 9:21