The spheres in the rotating frame now appear to be rotating, and should require an inward force to do that.

This required a structure that could withstand an inward force due to the pressure difference.

"Finally, inward and outward forces on the planet's orbit canceled each other out just before the star would have consumed the planet."

This means that the inward force on the vessel decreases, and therefore the aneurysm will continue to expand until it ruptures.

Bumping the key inward forces it deeper into the keyway.

He spoke at length quietly, but with such a kind of inward force and joy that one wondered how he could contain it.

The limit is obtained by setting the outward radiation pressure equal to the inward gravitational force.

As this happens, the outward pressures become insufficient to counter the inward force of gravity.

Atlantean shoulders, and the whole carriage heroic, with equal inward force to guide the great machine!

An inward force of gravity would therefore correspond to a negative-valued F(r).