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For Questions That Don't Merit Their Own Thread


Skyler4856
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13 minutes ago, Gargamel said:

Why is water noisy as  it heats to boil, and then gets quiet immediately before the boil, yet is appropriately loud when it is boiling?

science?

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19 hours ago, JoeSchmuckatelli said:

Those who don't know history are doomed to recreate it

And when they recreate it, they think it is something totally new and different.

2 hours ago, Gargamel said:

Why is water noisy as  it heats to boil, and then gets quiet immediately before the boil, yet is appropriately loud when it is boiling?

I've thought about this, too, especially when I make my daily bowl of instant grits or oatmeal or my evening hot green tea. It's really a fascinating thing about the properties of water, something we take for granted.

1 hour ago, kerbiloid said:

Because before it boils, the upper layer of the water is cool, so the bubbles implode on touching it.

And then they explode only on the hot surface.

Yes, sorta. As for the noise, it’s caused by cavitation, which is a high-tech way of saying bubbles form and then they pop. When you heat water on the stove, the layer at the bottom is the first to boil, meaning it turns into a gas. The water vapor collects into bubbles, which rise toward the surface, passing through cooler water en route. (Google for the win! :D)

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5 hours ago, SSTO Crasher said:

What causes Hawking radiation?

I think it happens because of the particles and anti-particles that spontaneously generate in all of space. (That's the reason you can never have truly empty space.) Normally, they cancel out, and nobody notices them, but when they pop up near a black hole, sometimes one particle is pulled in, and the other gets away. The flow of escaping particles is what we call Hawking radiation.

Anyone who knows better, please correct me if I'm wrong!

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7 hours ago, SOXBLOX said:

I think it happens because of the particles and anti-particles that spontaneously generate in all of space. (That's the reason you can never have truly empty space.) Normally, they cancel out, and nobody notices them, but when they pop up near a black hole, sometimes one particle is pulled in, and the other gets away. The flow of escaping particles is what we call Hawking radiation.

Anyone who knows better, please correct me if I'm wrong!

But I still don’t know why that causes the black hole to evaporate nor do I know why the process speeds up over time 

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28 minutes ago, SSTO Crasher said:

But I still don’t know why that causes the black hole to evaporate nor do I know why the process speeds up over time 

This may help out.  The intro covers the basics of it, but he goes on a deeper dive:

 

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37 minutes ago, SSTO Crasher said:

But I still don’t know why that causes the black hole to evaporate nor do I know why the process speeds up over time 

The spontaneously creating/destroying particles(called virtual particles I believe) will normally attract each other and annihilate, returning the 'borrowed'  energy they came from.

If there is a steep enough force gradient, one of these particles can be turned from it's course and instead follow the gradient(in the case of black holes, this would be gravity of course, with smaller black holes having a steeper gradient).  With a black hole, the particle that is sucked in can never re-combine with it's sister particle, turning that sister particle from virtual to real.  Because the energy to 'create' that new real particle must come from somewhere, the energy is considered to come from the black hole(presumably the sister-particle that falls in will annihilate with a particle inside the black hole, reducing the energy of the black hole)

(I'm guessing the video explains this better however)

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Could you have a "star" made entirely of uranium? Somehow a cloud of uranium isotope ratio TBD collapses and forms an object that emits roughly the same power as the sun for an appreciable length of time. A reasonable proportion of the energy needs to come from fission rather than just gravitational collapse a-la https://en.m.wikipedia.org/wiki/Kelvin–Helmholtz_mechanism

I think an equivalent question is

Is there a negative feedback mechanism in the collapse of a cloud of uranium that will result in a steady power output.

 

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16 minutes ago, kerbiloid said:

Probably you mean this one.

 

Question Inspired by that post but that star just has some uranium in its atmosphere.

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6 minutes ago, Hyperspace Industries said:

Could you make a hot air balloon which was painted black, or transparent and working like a car in the sun, that heated itself with sunlight? (This might be able to reduce the mass of hot air balloons, allowing more payload.)

Probably, but why would you?

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6 minutes ago, Admiral Fluffy said:

Probably, but why would you?

The gains are probably meaningless, but it is an idea, and I like to think and figure stuff out.

The main benefit would be probably just fuel costs, and even that is minor.

Edited by Hyperspace Industries
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Just now, Hyperspace Industries said:

The gains are probably meaningless, but it is an idea, and I like to think and figure stuff out.

The main benefit would be probably just fuel costs, and even that is minor.

And the cost is not having control over your buoyancy, which seems pretty major.

(needing to wait until the air in your balloon is sun-heated also means waiting until the ambient air is also warmer and presumably reducing lift)

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25 minutes ago, Hyperspace Industries said:

Could you make a hot air balloon which was painted black, or transparent and working like a car in the sun, that heated itself with sunlight? (This might be able to reduce the mass of hot air balloons, allowing more payload.)

When I was a child I bought a present for a friend which was basically an enormous black plastic bag and a light string, you filled the bag with air and waited for it to take off.

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