# Gravity, heat, flooding, and centrifugal force on a tidal-locked planet

Hi. I'm a science fiction author whose first novel Hemispheres, published through RockHill Publishing, explored a tidal-locked planet (Gliese 581g) where a group of activists increased its rotation to bring daylight cycles to both hemispheres. Now I'm writing the sequel, and there's ecological terrorist acts going on (I can explain why but it's not relevant to the physics questions).

Question 1) One group is trying to increase the planet's rotation even faster. Since centrifugal force would be stronger, would this indirectly increase the effects of gravity on the planet (gravity growing stronger as the planet spins faster)?

Question 2) One group of ecological terrorists are attempting to speed the melting of the icecaps. Since the planet is no longer tidal locked, the Coriolis effect exists now and that, in addition to daylight cycles, creates heat and heat transfer that melts the icecaps causing flooding. How would a nefarious group increase the speed of this flooding taking place?

Thanks!

Mark

PeroK
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Question 1) One group is trying to increase the planet's rotation even faster. Since centrifugal force would be stronger, would this indirectly increase the effects of gravity on the planet (gravity growing stronger as the planet spins faster)?
The Earth's rotation decreases the effective gravity.

Janus
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To add to what @PeroK posted. the centrifugal effect acts outward from the axis of rotation. And gets stronger as you move away from the axis. Thus this effective weakening is zero at the poles, and increases as you move towards the equator. But it is a small effect for something the size of the Earth rotating once every 24 hrs.

As far as Coriolis effect goes. The transfer of heat from equator to poles does not rely on it. This is done by simple convection. Air is heated at the equator, rises and moves towards the poles were it cools, sinks and then moves back towards the equator. You get air circulation of warm air moving towards the Poles in the upper atmosphere and cold air moving away from the Poles at ground level. What the Coriolis effect does is change the pattern of this circulation so that it is no longer along a straight North-South line.

Since centrifugal force would be stronger, would this indirectly increase the effects of gravity on the planet (gravity growing stronger as the planet spins faster)?

That depends on what you mean with "the effects of gravity on the planet". Do you mean gravitational forces of the star acting on the planet or gravitational forces of the planet acting on something else that is located on the planet? For the second case it has already been mentioned that the gravity on the surface of the planet will be reduced at most places. It can (but don't need to) be increased on the poles (depending on the size of the core). For the first case you need to distinguish between the gravitational net force (which will be almosty unchanged) and the tidal forces (which will be increased around the aequator).

To add to what @PeroK posted. the centrifugal effect acts outward from the axis of rotation. And gets stronger as you move away from the axis. Thus this effective weakening is zero at the poles, and increases as you move towards the equator. But it is a small effect for something the size of the Earth rotating once every 24 hrs.

As far as Coriolis effect goes. The transfer of heat from equator to poles does not rely on it. This is done by simple convection. Air is heated at the equator, rises and moves towards the poles were it cools, sinks and then moves back towards the equator. You get air circulation of warm air moving towards the Poles in the upper atmosphere and cold air moving away from the Poles at ground level. What the Coriolis effect does is change the pattern of this circulation so that it is no longer along a straight North-South line.

That makes sense, thanks a lot!