General Physics Thread

Does anybody has any information on how much energy the reaction of francium with water would release ? I can't even find data on bond energies of francium.

edited 9th Dec '15 4:33:08 AM by Aetol

Worldbuilding is fun, writing is a chore

Francium is highly radioactive and undergoes radioactive decay very quickly. Pretty sure estimating a reaction energy would be impossible.

edited 9th Dec '15 4:35:06 AM by SeptimusHeap

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

Exceptionally strong and lightweight new metal: "A team led by researchers has created a super-strong yet light structural metal with extremely high specific strength and modulus, or stiffness-to-weight ratio. To create the super-strong but lightweight metal, the team found a new way to disperse and stabilize nanoparticles in molten metals."

Eating a Vanilluxe will give you frostbite.

'Oh look! Yet another fictional alloy that's stronger and lighter than titanium!'

Uh, hate to break it up to you Wiz, but that became reality.

"... FUUUUUU—!"

edited 25th Dec '15 7:58:29 AM by MarqFJA

Fiat iustitia, et pereat mundus.

Has anyone else read su3su2u1's Tumblr? He explains a lot of complicated physics simply, but there's also a lot of interesting stuff about things like the impossibility of a career in physics.

Blind Final Fantasy 6 Let's Play

I haven't.

New battery shuts down at high temperatures, restarts when it cools: "The first lithium-ion battery has been developed that shuts down before overheating, then restarts immediately when the temperature cools. The new technology could prevent the kind of fires that have prompted recalls and bans on a wide range of battery-powered devices, from computers to hoverboards."

Researchers' metallic glue may stick it to soldering and welding: "Experts in nanotechnology have developed a glue that binds metal to metal to glass to you-name-it, sets at room temperature, and requires little pressure to seal."

Gravitation under human control?: "Produce and detect gravitational fields at will using magnetic fields, control them for studying them, work with them to produce new technologies — it sounds daring, but one physicist has proposed just that in a new article. If followed, this proposal could transform physics and shake up Einstein's theory of general relativity."

Scientists create world's most expensive material, valued at $145 million per gram: "f your life’s ambition is to become very, very rich, consider getting into the business of producing endohedral fullerenes - the world’s most expensive material.

Scientists at Oxford University in the UK announced that a spin-off lab called Designer Carbon Materials is now producing endohedral fullerenes, and they recently sold off their first sample of the material to the tune of $US32,000 for 200 micrograms (1 microgram = one-millionth of a gram), which is about one-fifteenth the weight of a snowflake, or one-third the weight of a human hair.

First discovered in 1985, endohedral fullerenes are spherical carbon nanostructures that consist of a sturdy fullerene cage made from 60 carbon atoms, inside which the atoms of non-metals or simple molecules, such as nitrogen, phosphorus, and helium, are trapped.

These things aren’t just outrageously expensive curiosities - when they contain nitrogen atoms, they actually have the potential to change how we keep time, because of their extra long electron spin lifetime."

edited 12th Jan '16 3:10:30 AM by rmctagg09

Eating a Vanilluxe will give you frostbite.

Hi there, I'd need a bit of help with a calculation I'm doing.

Basically, this is the "tunnel through the Earth" thought experiment, where I'm trying to calculate the air pressure as a function of the distance to the center.

I'm making the following assumption :

1. It's possible to dig such a tunnel (obviously)
2. The mass distribution of the Earth is homogeneous. The mass removed by the tunnel is insignificant and ignored.
3. Only a negligible portion of the atmosphere
4. The air is an ideal gas
5. The temperature throughout the tunnel is constant and is T₀ = 293 K

I call z the distance to the center of the Earth. First, I need to know the gravitational acceleration g(z). According to the shell theorem :

g(z) = g0 * z / RE

where :

• g₀ is the gravitational acceleration on the surface
• R_E is the radius of the Earth

Then, I use the following equation :

dP = - ρ(z) * g(z) * dz 

where :

• P(z) is the air pressure
• ρ(z) is the air density

From the ideal gas law, I get :

ρ(z) = Mair * n / V = P(z) * Mair/RT0

where :

• M_air = 29.0e-3 kg/mol is the molar mass of air
• R = 8.314 SI is the ideal gas constant

So :

(RT0/Mair) * dρ = - ρ(z) * (g0 * z / RE) * dz

dρ / ρ(z) = - (Mairg0) / (RT0RE) * z dz

ln(ρ(z)) = - (Mairg0) / (2RT0RE) * z2 + K

We know that for z = R_E, we have ρ(z) = ρ₀, where :

• ρ₀ = 1.21 kg/m3 is the air density on the surface

So :

ln(ρ(z)/ρ0) = (Mairg0) / (2RT0RE) * (RE 2 - z2)

@@ρ(z) = ρ₀ * exp( (M_airg₀) / (2RT₀R_E) * (R_E ² - z²) )

Doing the math for z = 0 gives ρ = 5.70e161 kg/m3. This seems beyond ridiculous. It would mean assumption #3 is going to be wrong (the entire atmosphere would end up down that hole) and possibly #4 too (the air could become liquid or even solid near the center). Did I do something wrong ?

edited 13th Jan '16 9:17:57 AM by Aetol

Worldbuilding is fun, writing is a chore

Based on memory, that result is not that ridiculous. Remember that Earth's radius is much larger than the height of the atmosphere, if atmospheric pressure can jump tens of orders of magnitude through its altitude, a pressure in such a tunnel can jump up to hundreds as well, even accounting for the shell theorem.

That formula does not account for the fact that the atmosphere does not have infinite mass. It would probably all collapse into that tunnel (gas is compressible), limiting the pressure generated (and disappearing outside of the tunnel).

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

So, I have a really, really, stupid question...

The smallest measure known is a planck length, right? And it is only theorethical?

It has always been the prerogative of children and half-wits to point out that the emperor has no clothes

The Planck length is a dimension at which under crude General Relativity + Quantum Mechanics physics everything is a black hole.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

... Crude? What does that mean?

... Someone should note that on whatever trope that involves digging a tunnel from one end of the planet to the other.

edited 13th Jan '16 9:46:38 AM by MarqFJA

Fiat iustitia, et pereat mundus.

A length of exactly one planck length has no particular significance. It's just a useful order of magnitude.

Worldbuilding is fun, writing is a chore

If it has no particular significance, then there would be no point in defining it in the first place. The fact that Planck defined it means that it does have significance.

Fiat iustitia, et pereat mundus.

There is a bit of significance to the lengths l1 and l2 in (Rotational momentum quantum)/(v*l1)=l2*c²/(G*2), though. Basically, under some common readings of the Heisenberg uncertainty principle (the first part of this equation), to each length there corresponds a mass and by General Relativity to each mass a Schwartzschild black hole radius. If l1 is so small that l2 becomes l1=l2*2, then each distance is a black hole. A distance so short that l1<l2*2 would be hidden behind its own event horizon.

(v is a speed, which can be no larger than c. The parameter of 2 at l2 reflects that l2 is a radius and l1 is usually taken as a diametre, if I understand that particular reading of the Heisenberg equation correctly)

edited 13th Jan '16 10:04:48 AM by SeptimusHeap

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

Well I am ignorant and all you young fancy people with yer fancy numbers scare me so I am not actually afraid of making myself look like an idiot because....well. I already am.

We know of stuff smaller than an atom, right? Could...uh. You know. theorethically something exist that is less than an atom in length? Which could CUT said atom in half?

It has always been the prerogative of children and half-wits to point out that the emperor has no clothes

Planck length is much smaller than atom diametre - 20 or so orders of magnitude smaller than a proton.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

Could it cut an atom in half?

It has always been the prerogative of children and half-wits to point out that the emperor has no clothes

Back to the tunnel through the Earth : trying to fit the entire atmosphere in there (assuming a circular section, radius = 1 m) gives us a pressure at the center of 235 PPa (that's petapascal). Air would be solid at such pressure, so the actual answer is even more complicated.

That's called nuclear fission. It does not actually involve a planck-length blade though.

edited 13th Jan '16 10:17:35 AM by Aetol

Worldbuilding is fun, writing is a chore

That's how a nuclear reactor or a nuclear bomb works.

Keep Rolling On

More math : if I account for the pressure of outer space (let's say 1e-10 Pa), then the pressure at the center climbs back up to a ridiculous 4.71e151 Pa. So, even if the sides of the tunnel can be stabilized somehow, it will still fill itself from the ends.

Worldbuilding is fun, writing is a chore

But...is it possible? Theorethically, I mean, for something much thinner to cut an atom?

It has always been the prerogative of children and half-wits to point out that the emperor has no clothes

Not really, an atom nucleus does not behave like a solid object at all. Nothing at these scales does.

edited 13th Jan '16 10:32:43 AM by Aetol

Worldbuilding is fun, writing is a chore

Yes, atoms are not solid objects. They are piles of droplets of gluons which contain quarks. None of these objects are solid except for particles which have suitable interactions.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

Ok. Got it. Atoms and anything smaller are basically cthulhu.

It has always been the prerogative of children and half-wits to point out that the emperor has no clothes

No, it's not that esoteric. Atomic nuclei are just aggregations of discrete subatomic particles. Subatomic particles, on the other hand, are themselves composed of specific formations of quarks... and possibly some sort of spherical "covering" (don't ask me where it comes from), if we take all of those physics models of the structure of subatomic particles literally. That is one clear distinction between atoms and particles, I think: At atomic scales, you theoretically can easily tell that an atomic nucleus is comprised of discrete physical units, whereas theoretically cannot do the same with subatomic particles. (Of course, I could be entirely wrong on everything after the ellipsis, so feel free to correct me.)

AFAIK, no respectable physicist has any idea if there is anything even smaller than quarks. So a better question is whether or not you can split a quark.

edited 13th Jan '16 11:00:55 AM by MarqFJA

Fiat iustitia, et pereat mundus.