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Comment by sroussey | Hacker News Reader

The Earths rotation already generates power for us: wind. It’s why the jet stream only goes one direction.

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.

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.

Also relevant is that the oceanic bulge is along the elliptic, but the earth's axis of rotation is tilted. So the effect can vary by latitude.

Wind power is mostly due to solar energy. Earth's rotation contributes a very small amount and even that smaller effect is more located in the upper atmosphere where we don't collect wind power versus solar caused pressure gradients

While true, if the earth stopped rotating the sun would also stop being "evenly" distributed around the globe, which would affect wind patterns a lot

a substantial amount of wind is also caused by (differential) solar heating: that's why wind doesn't only go in one direction

if you've ever spent time at the seashore, the wind comes in off the sea during the day (because of rising thermals on the land side) and blows back offshore at night (because the land cools and the sea is now warmer) that time in between the air is dead-still, and that's when the swarms of gnats can find you.

But the earth's rotation makes the solar heating _differential_

If the earth didn't rotate the differential would be permanent...and permanently in one direction

> It’s why the jet stream only goes one direction

Yet local winds blow in almost every direction. So to access that energy you'd need a structure 5 miles tall.

Or a balloon or kite five miles up.

Foucault's pendulum also orbits in one way, but is that generating more power than put into it by starting it off?

Isn't that more of the sun+rotation?

Is it possible to speed up the wind?

Yes that's how airplanes work

Yes, run power to wind turbines to use them as giant fans

Sure, cause constant heating and cooling and loop it.

None of the power comes from the Earth's rotation. Angular momentum is conserved in a closed system.

But it isn't a closed system. Tides transfer angular momentum from earth's rotation to the moon's orbit.

I was responding to a claim about wind. Yes, we can extract energy from tidal forces.

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