Wikipedia:Reference desk/Archives/Science/2015 February 28

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February 28

Why do we store energy in a battery, and not in a big capacitor?

Could we use a capacitor (static charge) instead of a battery (electrochemical reaction)? I wonder whether the capacitors would have more cycles of charge/discharge, whether the capacitor could be charged faster and be safe, and what would each solution cost. --Fend 83 (talk) 00:27, 28 February 2015 (UTC)

Batteries operate at constant voltage (roughly) whereas a capacitor's voltage is directly proportional to its charge state, so you need some electronics to use a cap. The main problem is that the cap can only store a small amount of energy per unit weight or volume, compared with a battery. The advantage is that it can handle very high currents, and last for many cycles. Using both a cap and a battery can be an optimum solution. Greglocock (talk) 00:41, 28 February 2015 (UTC)

Even high quality Batteries are multiple times cheaper in a cost/storagecapacity comparrison. Interest however is very high and allot of research is focused on making better capacitators. See Supercapacitor for current "state of art". --Kharon (talk) 01:53, 28 February 2015 (UTC)

Note also per our article, specifically Supercapacitor#Energy density and power density, the energy density of 2013 super capacitors can't even match a lead acid battery, let alone the various lithium-ion types. So even if you ignore cost and the other issues, super capacitors wouldn't work well in something where energy density matters, like most portable devices (e.g. mobile phones, tablets, notebooks, cameras, powerful torches, portable speakers) or electric cars. (Were it not for cost, there would probably be some places where they could be used where energy density doesn't really matter, and of course there are a number of use cases where they are suitable despite the high cost, usually where you don't need that much capacity but want the other advantages.) Nil Einne (talk) 12:31, 1 March 2015 (UTC)

• I've tried for days to find the source, which may have been Discover or Scientific American, but failed, so I will just mention this anyway. At the time I read an article about carbon-nanotubule capacitors, it said the main advantage, quick charging ability, was also a disadvantage, in that it meant the possibility of a catastrophic immediate release of the charge whic might cause a fire, explosion, or burn out your device. μηδείς (talk) 17:25, 2 March 2015 (UTC)

Moving in space

If a person is inside a box in space, can he shake, move or spin the box somehow? Can he change the center of mass of the box + he when moving around?--Noopolo (talk) 16:46, 28 February 2015 (UTC)

Assuming you mean the box contains life-support such as breathable air and is in empty space a long distance away from any other masses like our planet and it is kept closed and it has no rocket engine or other means of propelling it like a robotic arm or hatch to toss objects or even vents to expel gas into space with, then it is a closed system and the person would be unable to change the box + person's system's mass center, otherwise to cause motion of the mass center would produce an acceleration and momentum change in violation of conservation of momentum. The box will still be moved though in that the box will oscillate and/or rotate about the system's mass center in reaction to the person pushing or pulling on it in accordance with Newton's third law of motion. --Modocc (talk) 17:43, 28 February 2015 (UTC)

He can, however, cause the box to spin, (and stop spinning, pointing in a different direction) by spinning a gyroscope in the opposite direction. This is basis of reaction wheels. -- LongHairedFop (talk) 17:50, 28 February 2015 (UTC)

He could also move the box linearly, for a short period of time. That is, from when he kicks off from one side to when he hits the other side, cancelling his and the box's motion. StuRat (talk) 20:09, 28 February 2015 (UTC)

@LongHairedFop, @StuRat. Maybe I wasn't clear or detailed enough, but I actually covered those cases when I said the box can be oscillated or rotated (spun). Indeed, the person will almost certainly tend to spin the box (a gyroscope would have to be attached to the box for it to work and wasn't included in the OP's question although linking to it and the article on reaction wheels is still good additional reference material). The reason for the spinning is that when they push or pull on the box there will most likely be a nonzero torque acting through its center-of-mass. --Modocc (talk) 20:26, 28 February 2015 (UTC)

• This is rather obvious, just like a boat on a small lake, if he could rest his hands on both sides and rock back and forth, to an external observer the vessel would rock back and forth, while the center of mass of the entire system would stay in place (or steady motion). μηδείς (talk) 00:08, 1 March 2015 (UTC)

If you accept Modocc's constraints, then certainly all the guy can do is cause the box to spin or to briefly move to one side or the other as the center of gravity of the box+human stays at the exact same position. But our OP did not stipulate such limits...so let's explore the other options:

• If we are reasonably close to a star, then we could imagine the person rotating the box so that the orientation to the incoming sunlight would change. Clever application of Radiation pressure would allow the box to be moved, and even controlled by rotating the box to changes the cross sectional area of the box exposed to the light and the orientation of the facets of the box to the light. Sadly, radiation pressure is a very, very gentle force - so it would take a very long time to have much impact on the position of the box.

• If you allowed one side of the box to heat up in the sunlight, then depending on what it's made of, it might start to out-gas, producing a small thrust...and again, you'd have a small measure of control.

• If you could (for example) drill a hole in the side of the box to allow some air or waste water to jet out, then you'd have a primitive thruster that could also be used to provide control...albeit only for as long as you have material to eject from the box.

SteveBaker (talk) 07:54, 1 March 2015 (UTC)

Wherever he is if the box isn't insulated well, he could just sit in a corner and contemplate his fate for being the unfortunate lost stowaway trapped in an ejected shipping crate, then his body heat against the side would raise it a few degrees... not that the almost insignificant motion that this additional radiation and/or out-gassing would cause would matter to them. --Modocc (talk) 12:52, 1 March 2015 (UTC)

Extreme sexual practices

If you do a search for "hot kinky jo" on a popular pornography web site, which I won't name because I don't want to be seen as trying to spam, you can find video of a woman performing some extreme anal play. During her videos, she regularly:

• Puts what looks to be a 24" long (maybe 1-1.5" diameter) flexible dildo in her anus to the point that it can no longer be seen.
• Doubles that dildo and sticks both ends in her anus so far that the point where it bends is also inside her unseen from the outside.
• Puts what looks like maybe a 12-14" long and 3" diameter not-as-flexible dildo inside her.
• Has other women anally fist her up to their elbow where their fist can be seen bulging her abdomen.

My questions are many. How is this possible? I'm assuming some sort of training would need to be done with successively larger toys. Would there need to be some surgery performed to allow this? I've seen people have strange surgeries performed but this would blow my imagination. What is the longest flexible dildo that she would be able to use? Our large intestine article mentions that it is 4.9' long, so would that be the theoretical maximum that her body would be able to accept? I'm assuming that she uses an enema before (and possibly after to avoid infection even from cleaned toys) all these scenes since none of the toys come out with visible feces on them. Would she still be able to defecate normally? Would she be incontinent?

I'm completely serious in my curiosity here. I have an interest in extremes that people take their bodies to and this seems very extreme indeed! Thanks for answering and taking this is in good faith. 69.54.18.63 (talk) 18:19, 28 February 2015 (UTC)

The intenstines are way more flexible than any useful dildo, so five feet is out of the question. A foot seems on the high end, according to these butt-stuffers. InedibleHulk (talk) 18:28, 28 February 2015 (UTC)

Also remember that a flexible dildo is a squishy dildo. What looks like two feet, outside, will compress a bit. InedibleHulk (talk) 18:30, 28 February 2015 (UTC)

• Men have died from being penetrated by stallions. See this case from Washington state, where it was apparently legal. But we cannot comment on the law in Vermont or the safety, so you should contact a lawyer and a proctologist/gynecologist or at least your primary care physician in Vermont before engaging in any similar activity. μηδείς (talk) 20:25, 28 February 2015 (UTC)

WHAAOE - see Enumclaw horse sex case. Tevildo (talk) 21:08, 28 February 2015 (UTC)

Apparently the deceased should have been saying "Whoa!", not "Whaaoe!" μηδείς (talk) 00:05, 1 March 2015 (UTC)

British moment: Insert Camilla joke here. - ¡Ouch! (^{hurt me} / _{more pain}) 13:15, 4 March 2015 (UTC)

Mass bombardment 3.9 billion years ago and life

I was reading a review of Bill Nye's book Undeniable. It says "A heave meteorite bombardment some 3.9 billion years ago probably sterilized the planet, yet chemical evidence of life appears in rocks some 3.8 billion years old." Is it likely that the bombardment destroyed all life or proto-life? Bubba73 ^{You talkin' to me?} 19:35, 28 February 2015 (UTC)

He's referring to the late heavy bombardment. Scientists are unsure how serious this event really was, how long in duration, or if it even actually occurred. A sufficiently large bombardment could have sterilized the Earth. However, as the evidence on when life arose moves earlier and earlier it makes it appear more likely that perhaps at least some life already existed during and survived the late heavy bombardment. The presence of life markers close to the time of the late heavy bombardment is one of the arguments often used to suggest that the bombardment perhaps wasn't as severe as first speculated. At present, we don't really know. Dragons flight (talk) 19:53, 28 February 2015 (UTC)

When you consider that Endoliths have been found 3km below the surface of the earth, and are believed to exist as deep as 4.5km. We'd have to ask whether that bombardment would have been enough to make much of a difference that far below the surface. It seems entirely plausible that something might have survived. Our article on the Late heavy bombardment points to several sources that back up this idea. SteveBaker (talk) 01:54, 1 March 2015 (UTC)

Resolved

Thank you - I thought it seemed unlikely that everything should be wiped out like that. Bubba73 ^{You talkin' to me?} 03:56, 1 March 2015 (UTC)