1

Technology / Re: Does cold weather damage the batteries used in an EV?

« on: 13/01/2025 14:56:55 »

The Ford Pinto, a petrol(gasoline) car was prone to self cremation, as far as I remember.

Pintos caught fire because the tank ruptured in a rear end crash. There was famously the scandal when the cost-benefit memo was leaked showing that it was cheaper to keep paying compensation to the victims than modify the car.
https://en.wikipedia.org/wiki/Ford_Pinto#Cost%E2%80%93benefit_analysis,_the_Pinto_Memo

The perceived difference in risk is due to the fact that ICEs don't spontaneously combust. The usual point of unintentional ignition occurs when a poorly-maintained vehicle has been running fast and hot, the fuel line comes adrift or the carburettor (remember those?) floods, and a backfire on overrun blows flames out of the air intake.

I doubt that. I'd say more fires are fairly spontaneous electrical faults (unless the regular servicing schedule entails checking every electrical contact in the car for corrosion/looseness/overheating).

"Electrical faults with the 12-volt battery system are the most common cause of car fires, according to the AA's technical expert Greg Carter."

The fire I watched in the Cortina started after the owner had already reported an electrical fault, and the garage mechanic had thought he'd managed to fix it (everyone watching was expecting the fuel tank to explode, but judging by the way the fire brigade behaved, they knew it wouldn't). The near-fire in my Carlton was the heated rear window fuse incinerating the fuse box. Then there was the spate of Zafira fires which were also faulty maintenance of the electrics.

There is probably nothing incorrect in that ode to the EV but it paints a misleading picture. Okay, an ice will max out at ~40% but the other 60% is available for heating the vehicle whereas an EV which is already 40% down in these cold temperatures will have to use a lot of battery power just to maintain a survivable environment- just what the range will be I don't know but it will be impaired. I cannot imagine fuel consumption increasing during a cold snap unless road conditions prevent the vehicle from reaching an efficient speed/gear ratio. Cold dense air generally improves the efficiency of an ice.

He seems to be confusing a low efficiency with a large variation in efficiency with temperature change.

Personally, when I look at the state of cars these days, BEV or ICE, I'm glad I gave up driving.

2

Technology / Re: Does cold weather damage the batteries used in an EV?

« on: 12/01/2025 12:45:20 »

Battery cars are a victim of the availability heuristic: if something springs to mind more readily it will be perceived as more probable, BEV fires make news but ICE fires don't. People are used to the idea that petrol catches fire, it's not news, but for the best part of a century people have seen batteries as innocuous and harmless, so the idea that they're no longer so benign is more sensational. Everyone jumped to the conclusion that the Luton airport car park fire was a BEV when it wasn't.

Stats on the subject are still thin on the ground, but ICE cars are between 2 and 20 times more likely to catch fire than a BEV.

The only car I've ever watched burn was a Mk3 Cortina (electrical, not the petrol tank), although my Carlton came quite close to it one morning (again, electrical).

3

General Science / Re: What would the kinetic energy of a bullet falling from 2Km be?

« on: 20/12/2024 11:05:39 »

I recall a farmer demonstrating the difference between a rifle and a shotgun. He fired both into a thick wooden board from about 2' away, and they both made a neat hole in the front the size of the bore. On the back, the rifle hole had a couple of small splinters, and the shotgun hole had a patch about 3" diameter split away.

4

General Science / Re: What would the kinetic energy of a bullet falling from 2Km be?

« on: 12/12/2024 10:51:53 »

This thread reminds me of a day I walked through a hail of clay pigeon shrapnel, you'd think someone would have the sense not to hold a shoot over a public right of way, really.

As I keep pointing out to cyclists who like to refer to the difference in kinetic energy between a car and a bike, kinetic energy isn't really a very useful metric for gauging the potential to cause harm: the kinetic energy of a 72kg cyclist travelling at 12mph is exactly the same as Dirty Harry's Magnum 44 (1037J, 16g & 360m/s, to save you looking it up).

Energy lost on impact is a big step in the right direction but even that doesn't cut the mustard, as a simple thought experiment demonstrates. If a stuntman jumps from a skyscraper, the outcome will be very different depending on whether he lands on the pavement or an airbag, even though the terminal KE and total dissipated energy are the same in each case.

What differ are contact area and modulus of the materials, hence stopping distance & acceleration, hence force & pressure.

5

Physics, Astronomy & Cosmology / Re: How does H20 wear away stone?

« on: 03/12/2024 12:39:22 »

https://www.youtube.com/shorts/YrEgZoC2vo8
https://www.youtube.com/shorts/DMYazT57QIc

6

General Science / Re: Can an electron travel a bit in a copper wire for inertia?

« on: 24/11/2024 12:22:29 »

With a 1A current flowing in a 2mm diameter copper wire for example, an electron drifts at 23 microns/sec, so it would take 7 minutes to drift 1cm. Compare that with 1570km/s that electrons travel at anyway, in the absence of a current.

https://en.wikipedia.org/wiki/Drift_velocity

That said, you can't change an electrical current/voltage instantly because of circuit inductance and capacitance. (You can't shear a wire instantly either, as the cross section progressively reduces, so does the conductance and current.)

7

Physics, Astronomy & Cosmology / Re: What Causes This Optical Effect?

« on: 22/11/2024 12:18:35 »

It's not about interior vs exterior, it's lighter side vs darker side.

When you look from the brightest lit side to the darker side, the light reflected off the window/net curtains/ half-silvered mirror is greater than the light transmitted through it from the darker side, so you only see the reflected light because your eye doesn't have sufficient dynamic range to see both.

Move to the darker side, and the light transmitted from the bright side is greater than the light reflected from the dark side, so you see through.

The way to see the "wrong" way through a "one way mirror" is to put your face right up against it, and shade around your eyes with your hands (the same way oscilloscope hoods work).

8

Physiology & Medicine / Re: What Are Chemical Burns?

« on: 19/11/2024 16:06:24 »

I've never had any problems chopping the stuff, but frying it makes me cough and splutter. I tend to scald my mouth eating it if I'm not careful too, because the spice disguises the temperature.

9

Technology / Re: After reading this, would you let AI drive your car?

« on: 18/11/2024 18:35:36 »

https://www.msn.com/en-gb/cars/news/everything-i-hate-about-modern-cars/ar-AA1qbMK4
https://www.msn.com/en-gb/cars/news/everything-telegraph-readers-hate-about-modern-cars/ar-AA1sZKUy?ocid=msedgdhp&pc=U531&cvid=de801d317ef8473f9065deb57ef318e9&ei=88

10

Question of the Week / Re: QotW - 24.11.08 - How effective are cancer screening tests?

« on: 12/11/2024 11:58:04 »

Has anyone ever looked at whether increase in PSA is more reliable than absolute PSA level?

11

Physiology & Medicine / Re: What Are Chemical Burns?

« on: 08/11/2024 12:27:35 »

There is some evidence that capsaicin can damage the nerve involved leading to a reduced effect over time but I am not so sure how true this is.

Might that not just be habituation? I like garlic, but I stopped bothering to put in when I realised that I couldn't taste it any more.

12

Question of the Week / Re: QotW - 24.11.08 - How effective are cancer screening tests?

« on: 06/11/2024 12:02:06 »

When I had my bowel tumour, the FOB test was negative even after I'd already seen blood in the toilet.

13

Physiology & Medicine / Re: What Are The Advantages To Taking Vinegar Everyday?

« on: 25/10/2024 13:52:25 »

Various sources of vinegar (apple cider vinegar, PV, TV and others vinegar) have been shown to potentially alleviate obesity, diabetes, cardiovascular, cancer and other health complications.

My flecainide acetate smells of vinegar.

14

Question of the Week / Re: QotW - 24.09.20 - What will wind farms mean for the weather?

« on: 14/09/2024 14:51:32 »

The total amount of energy present in weather phenomena, all provided by solar energy, is so great in comparison to the tiny pittance harvested by man that I reckon there would be no measureable effects even with the projected increase in wind farms. Possibly short range effects in the local vicinity of wind farms is all there would be.

I think solar could have quite an effect, hose black panels absorb the suns enery and only 20 percent is converted to leccy.

Lol

What do you think usually happens to the radiation from the sun?

Some of it gets reflected, but less if the albedo changes.

15

Physiology & Medicine / Re: What liquid solution is best for a portable commode?

« on: 08/09/2024 13:13:30 »

I used a commode in hospital once, and there wasn't anything in it other than what I deposited. Commodes are emptied immediately after use, unlike chemical toilets. I've been splashed by the water in an ordinary toilet on occasion, I wouldn't want that if it was corrosive.

16

Physiology & Medicine / Re: What Is The Role Of Bread In Human Nutrition?

« on: 23/08/2024 18:42:43 »

Medical Research Council nutrition recommendations from their DAPA toolkit. (No more than 50% of total calories from carbs.)

Data from the European Food Standards Agency here.

Bread is high in salt (the biggest source of salt in my diet), and unless it's baked by a local artisan baker it's classed as 'Ultra Processed' because of the preservatives in it. I recently switched to supermarket loaf which has no preservatives, but it does tend to feel more stale as a result. Wholemeal is better because it's higher in fibre.

Beer used to be safer than water because it's boiled during the brewing process, famously, it was the absence of cholera among brewery workers that led John Snow to the cause of the Broad Street cholera outbreak.

17

That CAN'T be true! / Re: Is potassium chloride explosive

« on: 20/08/2024 18:19:34 »

Another use for urine here:
https://twitter.com/twitrkshukla/status/1825936930334454106

18

New Theories / Re: What's the unit of Torque?

« on: 11/08/2024 18:56:24 »

If you have a spring that follows Hooke's law, the displacement, s is proportional to the force, f, and the area under the graph is the energy stored: E=fs/2, or E=TΘ/2 (ie the area of a triangle).

19

General Science / Re: Is the Curie Effect Reversible

« on: 06/08/2024 13:39:22 »

Some confusion, I think. A permanent magnet will become permanently demagnetised above the  Curie temperature but a piece of soft iron simply changes from ferromagnetic to paramagnetic, and this change is reversible.

Yes, of course, this. It's the armature attached to the stat contacts in the iron that's magnetised, not the calibrated pellet on the back of the bit.

I have two bits for this iron, one with a fine tip which barely gets hot enough to solder and one which is far too hot and actually glows faintly in the dark

Size and temperature are two independent variables. My bit of choice is the PTF-7: 600F is too cool and slow, and 800F just burns off the flux and oxidises too quickly, 700F is the Goldilocks temperature. The PTF is fine enough to solder SMDs, but short and stubby enough that it's thermal resistance isn't so high that the tip temperature drops when you solder something the size of a BNC socket.

20

General Science / Is the Curie Effect Reversible

« on: 30/07/2024 14:50:14 »

So this website says that the Curie Effect is not reversible: heating above the Curie point results in a permanent loss of magnetism.

This seems to contradict the operation of the Weller soldering irons that I spent my whole working life using: they have bits with a magnetic pellet that it releases a spring-loaded armature to open the switch contacts when the bit reaches it's set temperature and attracts it again as it cools.

Reading Wikipedia, they make no mention of whether it's reversible or not, and Chat GPT starts by saying that it is, then agrees with the site that says it isn't, then when I point out it's contradicting itself says that there are two Curie Effects: one reversible and the other not.

I see that the original site makes note of a separate effect that's not the Curie Effect, but which causes a reversible loss of magnetism which is progressive not sudden, but I'm sceptical that's what Weller are using, as without a sudden loss at a particular temperature, the switching point would be dependent on the armature spring as well as the bit, and much more difficult to calibrate. Weller call their system Magnastat without reference to Curie, and although they don't explain in any detail how it works, they do refer to a change in characteristics at a specific temperature.