Faster Spinning Earth: Gravitational & Centrifugal Affects

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Discussion Overview

The discussion explores the effects of a faster spinning Earth on gravitational and centrifugal forces, particularly as rotation approaches relativistic speeds. Participants consider the implications for mass increase, gravitational strength, and the potential for centrifugal force to influence whether objects remain on the Earth's surface or are flung into space.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that as the Earth's rotation speeds up, gravitational effects and centrifugal effects will change, with questions about which will dominate.
  • One participant suggests that mass increases with rotation, raising questions about how this would affect gravity if the rotation neared the speed of light.
  • Another participant compares centrifugal force to gravitational force, questioning which is stronger and providing calculations for centrifugal force at high speeds.
  • There is a mention of the theoretical possibility of using centrifugal force to fling objects into space, though concerns are raised about the strength of materials needed to contain such forces.
  • A participant expresses difficulty in understanding the mathematics involved but seeks to conceptualize the forces at play as rotation approaches relativistic speeds.
  • Some participants note that centrifugal force could render the Earth unrecognizable before relativistic mass increase becomes significant.
  • Discussion includes references to cosmic bodies, such as millisecond pulsars, that exhibit relativistic rotational velocities, suggesting exotic examples of extreme rotation.

Areas of Agreement / Disagreement

Participants express a range of views on the significance of gravitational versus centrifugal effects, with no consensus on which force would dominate or how the Earth's characteristics would change under extreme rotation. The discussion remains unresolved regarding the implications of these forces at relativistic speeds.

Contextual Notes

Participants acknowledge limitations in their calculations and understanding, particularly regarding the transition to relativistic speeds and the assumptions involved in their reasoning.

boffinwannabe
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what would the affects of a faster and faster spinning Earth be gravitationally? Mass increases with rotation i believe? If rotation neared the speed of light how much would the mass and gravity change?

I am wondering what is more significant, the gravitational affects or the centifugal affects? Would a hugely faster spin keep us firmer on the ground or fling us off into space?
 
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If you fasten a heavy weight on the end of a string and whirl it round your head, you would easily be able to break the string.
You can probably generate the equivalent of several kilograms of weight that way without having to get up a speed of more than 100mph.

On the other hand, the mass increase due to Kinetic Energy is probably in the order of the weight of a single atom.

So, which is stronger, centrifugal or relativistic gravitation?{Edit}PS Having had my curiosity tickled, I did the calculation - the correct figure for a 1kg mass at 100mph is rather more than my off-the-cuff guess. It doesn't significantly affect this answer - but it's surprising how big it actually is.
 
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So from your calculations AJ Bentley, is the velocity provided by the centrifugal force higher than the escape velocity?
 
I should say so - work it out yourself.
Even using a classical calculation of centrifugal force F=mv^2/r you get F=mc^2/r

c is 300,000,000 and the Earth is about 6,000,000 metres radius so the upward force on a 1kg mass would be 15,000,000,000 Newtons.
 
Whoa, hold on a sec...
Are you trying to fling something out into space using centrifugal force?

Well, it is theoretically possible, and the US government has explored it many years ago. Sorry, don't have a source.
Anyway, the main problem is the strength of the centrifugal containment prior to release. Be it a steel cable, carbon nano-tube, etc... the "cable" will snap well before escape velocity.
But, the theory itself is quite sound. That's why it was actually experimented.
 
im a non-phsycis non-maths guy who just finds the subject interesting but frustratingly dotn understand the maths to work things out. So I am really trying to envisage what happens to the Earth if its rotation were to approach the speed of light. I trying to understand what forces become dominant. So i understand that at those speeds the increase in mass is significant but my mind is asking what would this make the net gravity on Earth given the increase in the centrifugal force. If the Earth stopped spinning i understand gravity would still be the dominant force keeping us on the ground. Now I am trying to understand the other extreme. Keeping it simple and just working on the basis that the rotation is near the speed of light and no worrying if the increase in rotation from was sudden or slow.
 
boffinwannabe said:
what would the affects of a faster and faster spinning Earth be gravitationally? Mass increases with rotation i believe? If rotation neared the speed of light how much would the mass and gravity change?

I am wondering what is more significant, the gravitational affects or the centifugal affects? Would a hugely faster spin keep us firmer on the ground or fling us off into space?

Centrifugal force would make the Earth unrecognizable long before relativistic mass increase becomes relevant.

Are there actually any cosmic bodies having relativistic rotational velocities? This is certainly very exotic.
 
Dr Lots-o'watts said:
Centrifugal force would make the Earth unrecognizable long before relativistic mass increase becomes relevant.

Are there actually any cosmic bodies having relativistic rotational velocities? This is certainly very exotic.

Well, some of the fastest millisecond pulsars can have surface velocities in excess of 10% of the speed of light, if I didn't screw up the calculation (12km radius object, rotating at 500-800 rev/sec).
 

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