Science desk
< October 9	<< Sep \| October \| Nov >>	October 11 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

October 10

Largest Snake

What's the world's largest snake? VeenM64 (talk) 02:16, 10 October 2017 (UTC)[reply]

Heaviest: green anaconda. Longest: reticulated python. See list of largest snakes. StuRat (talk) 02:44, 10 October 2017 (UTC)[reply]

Ever: Titanoboa (extinct). 2606:A000:4C0C:E200:9C22:2C7C:65A6:B9DA (talk) 02:55, 10 October 2017 (UTC)[reply]

That's "known", 2606; not "ever". You need to learn about unknown unknowns. μηδείς (talk) 20:59, 10 October 2017 (UTC)[reply]

I am an unknown unknown. 2606:A000:4C0C:E200:852E:7393:15B7:B79E (talk) 03:24, 11 October 2017 (UTC)[reply]

Scientists started measuring the ouroborus in Ancient Egypt and still haven't finished. But yeah, that's cheating. Sort of. InedibleHulk (talk) 03:35, 11 October 2017 (UTC)[reply]

Battery

why electro cars have lithium battery not lead? Why gasoline cars have lead battery, not lithium? — Preceding unsigned comment added by 31.4.151.139 (talk) 18:21, 10 October 2017 (UTC)[reply]

Different applications mandate different solutions based upon need and price. A gasoline engine needs a battery for temporary powering of electrical components, and mostly for getting the gas engine started from cold. This does not require a high storage capacity. For that purpose, a lead battery is far cheaper than a comparable lithium ion battery. On the other hand, an electric car is powering its motors with the battery, and so needs a large capacity battery with lots of energy releasing over a long period of time. A lead battery capable of doing that would be extremely heavy, if even possible. A lithium ion battery, on the other hand, can provide a light weight, dense energy storage format. --OuroborosCobra (talk) 18:42, 10 October 2017 (UTC)[reply]

Cost. I have a rather high-end battery in my shooting brake. I replaced it about 6 months ago and the cost was $160. That is for a high-end battery. You can get a cheaper one for under $100. The lithium batteries are light, which is necessary for electric cars, but also very expensive. My brother has a Chevy Volt. When his battery was barely charging enough for a 10 minute drive, he had to replace it. A refurbished replacement was over $500 (I don't know exactly how much as he was embarrassed to tell me). So, as a car manufacturer, assume that there is a $400 difference in cost for a car part. You will pass that on to the consumer. Will a consumer pay $400 more for the car and then be willing to pay over $500 to replace the battery in the future? Probably not. You are better off using a lead-acid battery in the car. 209.149.113.5 (talk) 18:49, 10 October 2017 (UTC)[reply]

Lead: heaviest common metal. Lithium: lightest metal. When you just need protons to hold your electrons when you're not using them all those extra protons (2000x electron weight) holding electrons too tightly bound to be used and neutrons binding the protons just add weight. Downside is lithium is expensive. Not gold expensive but still much more then lead. Lead even requires more neutrons per proton to avoid being radioactive than lithium because the atom is so big (biggest non-radioactive atom) Sagittarian Milky Way (talk) 19:02, 10 October 2017 (UTC)[reply]

From our article on Energy density:

Specific energy in megajoules per kilogram (MJ/kg):

Battery, Lead acid: 0.14 MJ/kg
Battery, Lithium ion: 0.46-0.72 MJ/kg
Gasoline (petrol): 46.4 MJ/kg

--Guy Macon (talk) 19:41, 10 October 2017 (UTC)[reply]

Caveat lector: you should divide the last line by 2-3 before comparing it with others, because that figure is the thermal energy you will get into the gases from the combustion of gasoline, but recovering mechanical work from that is hard. See [1] (though the drivetrain etc. losses are the same for an electric or gasoline engine, "engine losses" are close to zero for an electrical engine). Of course, fossil fuels are still a denser energy storage than battery (and much much much less than most things nuclear but the DeLorean time machine is not within current plans). Tigraan^{Click here to contact me} 19:54, 10 October 2017 (UTC)[reply]

Good point. A quick way to estimate engine efficiency is to look at how much waste heat an engine produces, counting the heat in the exhaust as well as the radiator. A 100% efficient engine would need no cooling. Electric motors get warm, but nothing like a gasoline engine. --Guy Macon (talk) 20:09, 10 October 2017 (UTC)[reply]

Still another nitpick: even with a "100% efficient engine" (no cooling required) you would lose some heat to the exhaust, because thermodynamics means you cannot save all the heat. The easy-to-memorize stat is that of three thirds of heat, you lose one third to thermodynamics (= exhaust), one third to the walls (= cooling), and you use one third (= mechanical work on the crankshaft). (Actually, how exactly thirdy the first third is can be easily computed with the compression ration of the engine - see [2] or Diesel_cycle#Maximum_thermal_efficiency.) (You probably know that, but readers may not.) Tigraan^{Click here to contact me} 20:33, 10 October 2017 (UTC)[reply]

I see that you assumed that by "engine efficiency" I was talking about engines with exhaust. I was mentally including electric motors, which are the engines in electric cars. Sorry for not being more clear. I do enjoy nitpicking though. You would be amazed at what some people think is fun. :) --Guy Macon (talk) 20:54, 10 October 2017 (UTC)[reply]

A consumer Lithium-ion battery will not work well at temperatures below 0°C but a consumer Lead–acid battery works in a range from -40°C to +60°C. A Lithium iron phosphate battery can work at -20°C but it has only a slightly better energy density compared to lead-acid.

Beside this major restrictions on a use as main car battery, lithium-ion batteries will very likely cause fires when damaged, which multiplies the danger when there is also a fuel leakage near. So its a very bad idea to combine both. On top a standard 12V 35Ah lead battery can be bought for 50$. A similar 12V 35Ah li-ion-Pack will likely cost you more then 300$. Last not least li-ion batteries need a Battery management system to balance the cells and a special charger as well as some care, while lead-acid batteries are usually install and forget today. --Kharon (talk) 21:19, 10 October 2017 (UTC)[reply]

Are sulfuric acid spills dissolving, carbonizing, dehydrating and heating any organic matter it touches less bad than the fires? Also reacting very vigorously and exothermically with water and contaminating the area with toxic lead or lead compounds. Also less gasoline to catch on fire or explode. Sagittarian Milky Way (talk) 23:11, 10 October 2017 (UTC)[reply]

The sulfuric acid in a lead acid battery is not concentrated, so although it may dissolve concrete, not much is done to organic matter. A human would easily survive the lead and acid for a while, but could not tolerate fire. Graeme Bartlett (talk) 09:31, 11 October 2017 (UTC)[reply]

I've started my diesel car with a 12v lithium battery and run it on that battery for short journeys when the alternator wasn't working. There might have been risks if the alternator had been trying to charge it. Dbfirs 07:34, 11 October 2017 (UTC)[reply]

Notice that electro vehicles like Teslas still have lead-acid 12 v batteries.B8-tome (talk) 11:09, 11 October 2017 (UTC)[reply]

I don't believe they do. Their main batteries are certainly Li-ion. Rmhermen (talk) 06:39, 12 October 2017 (UTC)[reply]

--Guy Macon (talk) 07:56, 12 October 2017 (UTC)[reply]

I had wondered if this was the case although I couldn't find it in our articles. Still should be pointed out that this is a lead-acid battery of about the same size doing about the same job as it does in an ICE car, not the main battery providing propulsion. Rmhermen (talk) 16:32, 12 October 2017 (UTC)[reply]

As others have said, you want lithium vs lead for energy intensive mobile applications, because the batteries are much lighter per unit of stored energy. But, if you compare either type of battery's energy density to gasoline, you have to remember that the battery is rechargeable while the gasoline is gone after you burn it. If you can recharge the batteries from renewable power, you're probably beating gasoline even with current technology, including counting all the infrastructure costs. 173.228.123.121 (talk) 21:03, 14 October 2017 (UTC)[reply]