Perceived Weight

[Steve Manning]

<mentor moved thread>

Suppose humans could travel quickly through deep space and are in search of an earthlike planet. A perfect planet is found, with the exception that its mass is huge, such that a human weighing x EarthKilos on Earth (1 G) now feels like he weighs 3x EarthKilos. So the strain on bodily parts might make this planet uninhabitable. And let's assume this new planet rotates once every 24 Earth hours. Would there be any difference in the perceived weight of an object, if that planet rotated every 15 hours, 10 hours, 5 hours, etc. ? Does centrifugal force have an offsetting force to gravity?

 

[PeroK]

Summary:: Is gravity offset by rotational forces?

<mentor moved thread>

Suppose humans could travel quickly through deep space and are in search of an earthlike planet. A perfect planet is found, with the exception that its mass is huge, such that a human weighing x EarthKilos on Earth (1 G) now feels like he weighs 3x EarthKilos. So the strain on bodily parts might make this planet uninhabitable. And let's assume this new planet rotates once every 24 Earth hours. Would there be any difference in the perceived weight of an object, if that planet rotated every 15 hours, 10 hours, 5 hours, etc. ? Does centrifugal force have an offsetting force to gravity?

Yes, effective gravity on Earth is slightly less than it would be if the Earth were not spinning.

https://en.wikipedia.org/wiki/Gravity_of_Earth#Latitude

 

[jim mcnamara]

Here is short discussion/calculation for "negating" 1G by speeding up Earth's rotation. The article states that the length of a full day for Earth would be 1.409 hours:
https://www.quora.com/How-fast-woul...ancel-out-our-gravity-At-least-at-the-equator

 

[DrStupid]

Here is short discussion/calculation for "negating" 1G by speeding up Earth's rotation. The article states that the length of a full day for Earth would be 1.409 hours:
https://www.quora.com/How-fast-woul...ancel-out-our-gravity-At-least-at-the-equator

It doesn't work that way. The article neglects the deformation of Earth due to the rotation. This deformation affects both the gravity and the centrifugal forces. That makes the calculation extremely difficult.

When I tried it for a homogeneous "Earth" I got a minimum length of the day of 2 hours and 40 minutes. At this point the minimum apparent gravity was still 5.6 m/s². I don't think that it can be completely eliminated. I didn't manage to decrease it below 3 m/s². Beyond that point there seems to be no hydrostatic equilibrium anymore.

The real Earth is not homogeneous, but I wouldn't behave completely different. It would just rotate a bit faster. I expect it to be ripped apart long before the surface gravity is completely compensated by centrifugal forces.