1

General Science / Re: How do we make synthetic gasoline?

« on: 22/05/2022 23:42:20 »

Ethanol would be great, methanol too, but they all come from plants in current form. We have trouble feeding the world at present, which means cutting down the forests and exterminating all the biodiversity.

I would have thought a mixture of different chemicals will provide the greatest effi iency. The idea of an Ice engine is not an explosion but an expansion in a similar way to gunpowder and petrol which has various different molecules there in, different chemicals expand at different rates.

2

Just Chat! / Re: Should we report all people to the police if we find them with child porn?

« on: 21/05/2022 20:08:03 »

Torturing someone to death because of their religious utterances cannot be considered a crime of greed or lust. What else motivates anyone?

Power and money? I have heard that on the odd occasion that these can be factors.

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Just Chat! / Re: Should we report all people to the police if we find them with child porn?

« on: 20/05/2022 15:43:56 »

. Every christian church has at least one graphic depiction of a hate crime,

In what way a hate crime? The rulers hated him?

4

General Science / Re: Is it safe to transport hydrogen gas compressed into a water tank?

« on: 18/05/2022 13:04:44 »

How about pipes, and huge gas storage containers dotted here and there
.

5

Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 17/05/2022 21:42:41 »

You would do well to review the basic physics of thermoelectricity. Standard thermocouples and thermopiles have a known temperature coefficient of voltage. If you buy a cheapish digital multimeter it will probably come with a Type K thermocouple and thermistor compensation block that you just plug in to the meter and measure temperatures to better than ±0.1K.

Come on, PC, this is very simple, robust engineering hardware. The guy who repaired my cooker had one in his bag.

Coefficients spake greatly of powered monitoring thus allowing as you say ohmic heating. Also if you never see a change how can you be sure that your measurement is correct. You need to alter the objects temperature.

6

Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 17/05/2022 18:10:27 »

At some point in your schooldays you should have been introduced to zero-current potentiometric measurements, the Wheatstone bridge, or some other classic null device. If not, I  can only recommend that you review a basic physics text. All we are doing here is a heat-flow null using rate of change to indicate the null point.

Here's a basic aircraft instrument panel. When the dial on the lower right shows zero  rate of change you are neither climbing nor descending so your lift vector equals your weight. 

It is true that some physics students (and some pilots) achieve a null balance by pure chance, but most of us do it by successive approximation.

Photon coupling with mirrors is not luck.

But the thermo couple is still not measured, unless you use a thermometer of a kind.

7

Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 17/05/2022 14:00:17 »

I'm not Alancalverd but the idea seemed to be that the thermopile was powered, or somehow heated, initially to raise it to a particular temperature.   Then it is switched off and can even be disconnected from any battery or circuit.
   For the second part of the experiment you just connect a Volt meter to the thermopile.   That's the basic idea of an idealised thermopile, it's a thing that doesn't need powering by a battery, it just generates a voltage entirely due to the temperature it has.   You can measure that just by connecting a volt meter.  An ideal volt meter has an infinite resistance, so we can imagine that (almost) no electrons need to flow for that measurement.

A thermopile is a series of thermocouples. If you know the temperature of one set of junctions then the voltage across the  others depends on their temperature difference - no external power involved. But if you break the circuit and inject some current you can raise the temperature of the assembly by ohmic heating. Come to think of it, I'd probably use an auxiliary heater, even simpler.

The theory of operation is then to raise the thermocouple temperature seperatley to the same and as yet unknown temperature of the object body. Connect them into one system by pure luck and register a zero voltage.

Firstly how do you know the temperature of the thermocouple if you are not withdrawing heat from it. Perhaps with another thermocouple? It would be classed as a single system

Secondly even though there is a remote possibility you may achieve equilibrium by pure chance is this really credible!

8

Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 16/05/2022 17:18:55 »

The spectrum is irrelevant. As long as the source and detector are coupled and isolated from the rest of the universe, heat always and only flows from a hotter body to a cooler one.
 

Is the thermopile powered, thus allowing you to deduce the electron flow, or is it passive, thus meaning you do not know the temperature of it?

9

Just Chat! / Re: A Short puzzle with dogs.

« on: 16/05/2022 10:36:43 »

Straight to the dog house and vertically down to the river.

   I guess that might work.   The original problem did ask you to find the shortest route for a thirsty dog to get home.  The dog did get home and it was thirsty.

Best Wishes.

It did, and it is possibly the shortest distance to answer the riddle. Conversely with the dog being thirsty it may be the quickest (shortest duration) for the dog to arrive immediately at the river and then toddle off home as the dog probably will function far better once refreshed.

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Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 15/05/2022 20:25:20 »

You look at the thermopile voltage and rate of change.

V α T_thermopile

dV/dt α ΔT (thermopile - fly)

It sounds in a similar fashion to the new fangled measurement of mass, the difference is that in the measurement of mass the system is distinct, but in the temperature measurement using a thermopile the subject and the device develop into one singular system and therefore only know the temperature of the combined singular system not the original object.

11

Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 15/05/2022 16:11:22 »

How do you detect it if energy is not leaving the system?

When you don't detect it coming or going, it isn't transferring. Therefore the subject and the reference must be at the same temperature.

A clever way to do this (at least in principle)  is to put your sample and a small thermopile at the foci of two spherical mirrors facing one another. You heat the thermopile by passing a current through it, and measure its temperature by measuring the voltage across it when you switch off the heating current. If the sample and the thermopile are at the same temperature its voltage won't change with time immediately after switchoff.  But as I remarked elsewhere, practical heat experiments are very difficult to do!  The experiment was originally devised in response to an interview question:how would you measure the temperature of a fly?

But how do you measure a lack of transfer. I understand the principle of  lack of  register but how do you tell the temperature. All I know is two blobs are in equilibrium.

12

General Science / Re: Is it safe to transport hydrogen gas compressed into a water tank?

« on: 15/05/2022 16:07:45 »

There is a reason pressurised containers are the shape they are.

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Just Chat! / Re: A Short puzzle with dogs.

« on: 15/05/2022 13:13:46 »

Hi.

   It might be time for a new and suitably short puzzle with dogs.

   Find the shortest route for a thirsty dog going home.

The dog starts  100 m  west of his home and  10 m North of it.    There's a river running west to east which is 30 m south of his home.   The dog must get home and get to river at least once on the way.    What is the shortest route?

Straight to the dog house and vertically down to the river.

14

Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 15/05/2022 12:36:56 »

Depends on what constitutes temperature? Is it on atomic level or subatomic level, is the temperature considered to be on the substance in question or the measuring device. For example how could you ever measure temperature without the substance in question loosing some energy.

Temperature is the mean internal kinetic energy of a mesoscopic body. It has no meaning for an individual particle.

You can in principle measure temperature without net heat loss by detecting the heat flow between the subject body at T_S and a reference at T_R. when there is no flow, T_S = T_R.

How do you detect it if energy is not leaving the system?

15

Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 15/05/2022 00:48:01 »

Depends on what constitutes temperature? Is it on atomic level or subatomic level, is the temperature considered to be on the substance in question or the measuring device. For example how could you ever measure temperature without the substance in question loosing some energy.

16

General Science / Re: How hot can two hairdryers make a charcoal foundry?

« on: 13/05/2022 08:20:01 »

You asked me; why not him?
Why are you still asking me about something which someone else wrote, and which is clearly wrong?

This video uses coal dust instead of charcoal dust, but I think it can represent my point.

I think most solids ability to combust is down to their fineness.

17

General Science / Re: How hot can two hairdryers make a charcoal foundry?

« on: 12/05/2022 13:34:17 »

I am not familiar with charcoals flash temperature

It doesn't have one.

I just googled it.

The flashpoint of charcoal is the temperature at which it will ignite and give off an open flame. The Flashpoint of Charcoal is 40 degrees Celsius. Dec 23, 2021

40c seems a bit low, at that temperature in hot countries you would not be able to smoke on a hot day. Wood and charcoal go through a couple of different stages of cumbustion. First they are heated causing the release of smoke from the wood as the cellulose decomposes, secondly the remainder oxidises. If the flash temperature of the vapour only needed to be 40c fires would not smoke I would not think.

18

Physics, Astronomy & Cosmology / Re: Why is leg room on transport so limited ?

« on: 10/05/2022 23:37:51 »

I have also thinned the wings in the new plane

The wings are also where they carry most of the fuel.
Is your new plane nuclear-powered?

As you may have deduced my plane requires less fuel.

19

Physics, Astronomy & Cosmology / Re: Why is leg room on transport so limited ?

« on: 10/05/2022 21:48:58 »

Makes you wonder why nobody has put wings on a train. Bloody engineers, always concerned about physics and safety. Fly the dream!

I have designed a new train..........


https://en.m.wikipedia.org/wiki/A%C3%A9rotrain

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Physics, Astronomy & Cosmology / Re: Why is leg room on transport so limited ?

« on: 10/05/2022 19:30:43 »

Why is leg room on transport so limited ?

Because most passengers don't want to pay extra for:
- An emergency exit row
- Business Class
- First Class
- Train as a pilot, so their seat can adjust to a comfortable distance

Business class and first does have significant weight additions with beds etc, but this weight and size remains the same. The emergency exits and aisles I suppose do take up a significant ammount of floor space, but less passengers less toilets less air ducting. Weight is the enemy in flight, not length.