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Can Earth's rotation generate power? Physicists divided over controversial claim

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Re: Can Earth's rotation generate power? Physicists divided over controversial claim

#181

Post by Detrytus »

DriverDaily wrote: post #130
ziofill wrote: post #25

Wouldn't this eventually slow down Earth's rotation? The rotational kinetic energy of our planet is 1/5 M * R^2 * w^2 with (approximately) M = 6e34 kg, R = 6.3e6m, w = 7.4e-5 rad/s, which gives approximately 5e36 joules. Yearly we need roughly 3e16 Wh. Yeah ok there's plenty. Woah! (also, I may be off by some orders of magnitude)

Can we put energy in to speed it up? That way a day can be 24 hours exactly instead of 23 hours, 56 minutes, 4 seconds, etc...

Don’t follow your logic: if the day is currently shorter than 24 hours we need to slow the Earth rotation down, not speed it up.

Re: Can Earth's rotation generate power? Physicists divided over controversial claim

#182

Post by Rury »

deepfriedchokes wrote: post #51
EncomLab wrote: post #45

It's incredible the lengths humanity is willing to go to avoid adopting nuclear energy - despite the US navy driving mobile reactors millions of miles over the last 70 years.

The Navy isn’t constrained by economics. Nuclear doesn’t make sense economically compared to things like solar and batteries.

> The Navy isn’t constrained by economics

And solar less so than nuclear. Nuclear receives only ~1-3% of energy subsidies in the US [1].

[1] - https://en.wikipedia.org/wiki/Energy_subsidies_in_the_United...

Re: Can Earth's rotation generate power? Physicists divided over controversial claim

#183

Post by mmooss »

timewizard wrote: post #154
deepfriedchokes wrote: post #51

Earlier quoted context omitted.

The Navy isn’t constrained by economics. Nuclear doesn’t make sense economically compared to things like solar and batteries.

> The Navy isn’t constrained by economics. In what way is it not? It has a budget and a mission. Economics are a huge part of their existence. Far more is spent on health care every year over the Navy.

The US Navy has other, very high priorities to balance against cost - national security, global security, freedom, peace, trade, the lives of billions, the lives of its own personnel. The US military may the largest budget of any organization in the world.

At the same time, they invest in those mobile nuclear reactors only for specific needs: attack submarines, ballistic missile submarines, and aircraft supercarriers. They calculate that the benefit of effectively unlimited fuel supply is worth the cost for those ships. The submarines can stay submerged for months at a time and have extensive range, and the carriers can move through the ocean, displacing 100,000 tons of water, to anywhere on the globe without worrying about the logisitcs of the enormous amount of fossil fuel it would require.

Re: Can Earth's rotation generate power? Physicists divided over controversial claim

#184

Post by pavel_lishin »

genewitch wrote: post #160
themaninthedark wrote: post #72

There was a decent science fiction serris based on this premise: https://www.goodreads.com/book/show/700919.Signal_to_Noise https://www.goodreads.com/book/show/737628.A_Signal_Shattere...

"Decent"

I thoroughly enjoyed them! I think I have both in paperback, though as a teenager, I managed to read them out of order.

Re: Can Earth's rotation generate power? Physicists divided over controversial claim

#185

Post by pavel_lishin »

Hyperboreanal wrote: post #115
Rygian wrote: post #73

Earlier quoted context omitted.

I've already read one where some weird alien ants hollow out the earth to make it spin faster, and take advantage of the increase in speed to generate power somehow (maybe by building a geostationary conductive belt around the planet, that acts as the "stator"?)

Saying what book you're talking about is kind of a spoiler now for anyone that happens to be reading its series. Are there spoiler tags on HN? The Long Utopia, book 4/5 of the Long Earth series by Pratchett and Baxter. The series has very meh characters/dialogue, excellent ideas and sense of nearly possibility-unlimited discovery that's executed very well, highly recommend if that's your cup of tea. Ended up skipping…

I was wildly disappointed in that series. A great premise that fizzled out about 3/4ths of the way through the first book. I powered through, and started the second, and gave up maybe five chapters in.

If the concept of world-hopping intrigues you, Charles Stross's "Merchant Princes" series does it better.

Re: Can Earth's rotation generate power? Physicists divided over controversial claim

#186

Post by antod »

logifail wrote: post #77
frozencooler wrote: post #42

Earlier quoted context omitted.

Doesn’t driving west to east on a highway slow down the Earth’s rotation, via the power transferred into the ground?

Reminds me of a glorious question from undergraduate physics: Calculate the change in the length of the Earth's day if the UK were to switch to vehicles driving on the right-hand side of the road rather than the left..

Is that due to all the roundabouts switching direction relative to the Coriolis effect? Hence the relevance of the UK?

Presumably without roundabouts it's all random directions and balanced?

Or am I barking up the wrong tree?

Re: Can Earth's rotation generate power? Physicists divided over controversial claim

#187

Post by [deleted] »

DriverDaily wrote: post #130
ziofill wrote: post #25

Wouldn't this eventually slow down Earth's rotation? The rotational kinetic energy of our planet is 1/5 M * R^2 * w^2 with (approximately) M = 6e34 kg, R = 6.3e6m, w = 7.4e-5 rad/s, which gives approximately 5e36 joules. Yearly we need roughly 3e16 Wh. Yeah ok there's plenty. Woah! (also, I may be off by some orders of magnitude)

Can we put energy in to speed it up? That way a day can be 24 hours exactly instead of 23 hours, 56 minutes, 4 seconds, etc...

[deleted]

Re: Can Earth's rotation generate power? Physicists divided over controversial claim

#188

Post by vikingerik »

kadoban wrote: post #111
kurthr wrote: post #105

Earlier quoted context omitted.

And don't forget the tides, both solar and lunar. I'm sure a large enough mirror and photocell could get power out of the aurora borealis. An argument that the magnetic field in a location remains completely constant as the earth rotates seems bizarre, but so does the idea that it's large enough to economically extract power.

Are the tides caused by Earth's rotation? My understanding is they're not. I know they're a bit of an inter-related system, but I thought if anything tides mess with rotation (eventually causing tidal lock), not so much the other way around. How big are the solar tides? Never really considered that tbh. Looked it up, they're about half the size of the Lunar ones? Wild.

Thermodynamically speaking, the energy in tides does come from Earth's rotation.

The moon raises a bulge in Earth's crust and ocean. Earth's rotation carries that bulge ahead of the Moon's position. The bulge pulls the Moon forward (raising it to a higher orbit), while the Moon pulls the bulge backward (slowing Earth's rotation.)

Once Earth's rotation slows enough, tidal lock is reached. Then the tidal bulge stays in a single place always pointed at the relatively non-moving overhead Moon, and there is no motion to extract energy from.

Re: Can Earth's rotation generate power? Physicists divided over controversial claim

#189

Post by thaumasiotes »

kadoban wrote: post #141
bmm6o wrote: post #114

Earlier quoted context omitted.

The short answer is that there would still be tides without rotation, but with a period based on the lunar cycle. We have daily tidal effects, the moon can't do that by itself.

Ah I see, that makes sense. Thanks.

The mental model I was presented with is that the ocean bulges toward (and, on the other side of the earth, away from) the moon, and the earth spins within the ocean. If you take a perspective that is fixed to a particular point on the earth, you'll see the tides constantly moving past, but that's an illusion just like the rising and setting of the sun. They're both really the rotation of the earth.
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