1

Physiology & Medicine / Re: Wintertime and Hand Washing. Whose Directions Do You Follow?

« on: Yesterday at 00:37:33 »

The Swarfega just removes the barrier cream

And then stops... by magic.
Because it knows that the greasy stuff that you put on your skin is different from the greasy stuff that's part of your skin.

2

Physiology & Medicine / Re: Does Your Brain Remember Everything?

« on: 06/12/2023 22:55:41 »

I thought I already replied to this...

3

Physics, Astronomy & Cosmology / Re: Has E=mc2 been proved practically?

« on: 06/12/2023 13:10:51 »

electromagnetic energy is massless

That's a matter of perspective. Light has no rest mass, but it has relativistic mass.

4

Physiology & Medicine / Re: Do tranquilizers really work as fast as we see in crime fiction?

« on: 02/12/2023 22:05:31 »

The idea- popular in cartoons and spy films- that you can knock someone unconscious with a blow to the head and have them recover fully, shortly afterwards, is as much a myth as the "chloroform on a cloth" myth.
It's probably more dangerous too- since not many people have ready access to chloroform.

5

Physiology & Medicine / Re: Do tranquilizers really work as fast as we see in crime fiction?

« on: 01/12/2023 17:59:59 »

It depends...
But.
" In 1865 as a direct result of the criminal reputation chloroform had gained, the medical journal The Lancet offered a "permanent scientific reputation" to anyone who could demonstrate "instantaneous insensibility", i.e. losing consciousness instantaneously, using chloroform.[62]"
From
https://en.wikipedia.org/wiki/Chloroform#Criminal_use

It would be tricky to balance a high enough dose to get a fast effect vs a dose that kills  the person.
Not a problem in the OP's scenario.

This sort of thing is a genuine concern.
https://en.wiktionary.org/wiki/chemical_cosh

6

Just Chat! / Re: Would you fart in an elevator?

« on: 29/11/2023 17:19:47 »

Farting in the lift is wrong on many levels.

7

Chemistry / Re: A machine that smells as well as a dog

« on: 24/11/2023 16:03:26 »

Two things.
Evolution has about a billion year head start on us and
there's no market because the machine would have to be cheaper to build than a dog.

8

Question of the Week / Re: QotW - 23.11.24 What can seeds to for our health?

« on: 23/11/2023 19:39:09 »

If you are careless when eating apples you should be glad that the pips go through unchanged.
If chewed they release cyanide- though not enough to do any harm.

Eating seeds is pretty much universal when you think about it; wheat, maize, rice and so on as well as pulses and nuts are essentially seeds.

9

General Science / Re: What happens when a superconductor is utilised in a circuit?

« on: 22/11/2023 18:30:48 »

One thing they do with superconductors is make electromagnets.
These often have large inductances.
Let's pick a number out of a hat and say it's 10 henries.

Imagine I connect a power supply to that coil and it has an output voltage of 10 volts.

Initially no current is flowing.
When I make the connection the inductance of the coil limits the rate of change of current.
The current will rise (from zero) initially at 1 amp per second.
After 10 seconds the current flowing will be 10 amps.
Imagine that I have things set up so that the coil is short circuited by a piece of "superconducting stuff" which is too warm to super-conduct.
Initially it makes no real difference. Some current flows in it but,  if I'm clever, not much.
But when the current reaches 10 amps, I cool that short circuit down and it becomes a superconductor.
The power supply is short circuited and so it blows a fuse or trips out or whatever.

But the current of 10 amps continues to flow in the coil and through the link (which is now cold enough to be a superconductor).

Equivalently, you can make a switch out of superconductive stuff and close the loop with that.

Interestingly, (almost) all the modeling of inductors and capacitors that you see in high school text books assumes that they have zero resistance.
All the maths you saw  was designed to work with superconductors :-)

10

Physics, Astronomy & Cosmology / Re: Temperature and k.e. : Does a substance cool down if particles break apart?

« on: 11/11/2023 15:48:18 »

I'm now trying to think of a situation where the effect would occur.

I think it's impossible.
If the "pairs" were so weakly held together that you could ignore the "bond energy" between them, then they would fall apart as soon as they bumped into each other.
If the binding energy was high enough to avoid that, then you could no longer ignore it when the molecules split apart- they would have a bit less kinetic energy after the split.

11

Physics, Astronomy & Cosmology / Re: Temperature and k.e. : Does a substance cool down if particles break apart?

« on: 11/11/2023 13:58:41 »

Imagine just one particle.
It falls apart into two but, thanks to momentum and energy conservation, the two parts must carry on along almost identical paths (and their CoG must follow exactly the same path).

So, each one has half the mass, but the same speed.
So it has half the  energy.

(and the overall energy is the same- obviously).

The temperature of a gas is a measure of the average energy per particle.
And there are now twice as many particles with only half as much energy each and that, in principle, means that the temperature has fallen by half.

I don't think it's a realistic scenario, but it's an interesting bit of thermodynamics.

12

Geek Speak / Re: How to make VLOOKUP tell the difference between zero & blank

« on: 28/10/2023 18:15:34 »

Can  you make a copy of the data but using  isnumber and isblank to clarify things for the lookup?

13

Physics, Astronomy & Cosmology / Re: The Color of Atoms.

« on: 23/10/2023 09:57:54 »

The problem is known and being worked on.
As a pilot, it's easy enough to put in charcoal filters to scrub out mercaptans for hydrogen used in fuel cells..
In the longer term there are proposals for using other stenching agents.
Another point is that it may be useful if "hydrogen smells different from gas".

https://www.sciencedirect.com/science/article/abs/pii/S0360319920306595

If we were able to magically stop using gas in pipes today and use H2 instead, my guess is that it would be 10 years or so before the network stopped stinking of mercaptans.
So, any "H2 for fuel cells" would still need a separate distribution system or a scrubber.
Fortunately, charcoal works pretty well.
Regenerating it would be interesting.

14

Physics, Astronomy & Cosmology / Re: Which bit of the Shell theorem is not working?

« on: 13/10/2023 17:09:53 »

Now, consider a particle of Hydrogen

The space is homogeneous for the purpose of this connundrum

Pick one.

15

Physics, Astronomy & Cosmology / Re: Which bit of the Shell theorem is not working?

« on: 13/10/2023 16:27:28 »

Which bit of the shell theorem broke down and why?

The assumption of homogeneity
Because stuff is made of atoms and molecules.

16

Physics, Astronomy & Cosmology / Re: What happens to the surplus electrons after an alpha decay?

« on: 09/10/2023 09:50:25 »

As far as I can tell, the thermodynamics that applies to chemical kinetics and equilibria would also apply mutatis mutandis to nuclear physics.
But the energies are something like a million times higher so the temperatures needed to affect the outcome would be about a million times higher.
The test tubes would melt.

17

Physics, Astronomy & Cosmology / Re: What happens to the surplus electrons after an alpha decay?

« on: 08/10/2023 23:31:02 »

At some point during the evolution of the cosmos, most planets were indeed smaller than a grain of salt. But the density of beta emitters was very small indeed.

Planet means "wanderer" and at that stage, they didn't.

18

Physics, Astronomy & Cosmology / Re: What happens to the surplus electrons after an alpha decay?

« on: 08/10/2023 17:51:11 »

consider a tiny grain of an energetic beta emitter like Yttrium-90.

I more or less did.

it might manage to boil itself.

Once the thermal energy is enough to " overcome the binding energy of the delocalised electrons " you no longer have a lump.
And I think that's about 6 or 7 orders of magnitude less than the nuclear energy available.There's also the question of "what is the boiling point of something in an absolute vacuum?" (It needs to be that good, in order to act as an electrical insulator.

It's interesting that your idea about a planet only works for planets that are smaller than a grain of salt.

Unless, of course they are flat-earth shaped.

19

Physics, Astronomy & Cosmology / Re: What happens to the surplus electrons after an alpha decay?

« on: 08/10/2023 15:09:16 »

Let's assume that the alpha emitting planet is bigger than a pea.

And let's assume that the range of alpha particles in solid matter is 100 micrometers.

What fraction of the alpha particles can actually escape?

After a while the planet would be hot.
And either thermionic emission of electrons or emission of helium ions (making their way out via diffusion) would ensure that the planet was electrically neutral and thus safe from that fate- though it might manage to boil itself.

The process where "internal coulomb repulsion overcome the binding energy of the delocalised electrons and blow the chunk of metal apart?"
Is (more or less) used in chemistry.
https://phys.libretexts.org/Courses/University_of_California_Davis/UCD%3A_Biophysics_241_-_Membrane_Biology/06%3A_Experimental_Characterization_-_Mass_Spectrometry_and_Atomic_Force_Microscopy/6.03%3A_Electrospray_Ionization_(ESI)_Mass_Spectrometry
It's called a coulomb explosion.
(Though, it's a very quiet "bang".)

20

Chemistry / Re: What types of plastic nbail polish remover can melt?

« on: 08/10/2023 12:53:05 »

Ethyl acetate will dissolve polystyrene, but acetone will just turn it into a sticky mess.
So the answer is "it depends" unless we know how much acetone is in the mixture.
Glycerine won't dissolve any conventional plastic (though it might dissolve polyvinyl alcohol).
Acetone or ethyl acetate will dissolve cellulose acetate.

Something like this chart may help.
https://www.plasticsintl.com/chemical-resistance-chart