Wikipedia:Reference desk/Archives/Science/2015 April 12

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April 12

Palm tree

Palm tree in the Canaveral National Seachore

the palm in the forefront has not had the "boots" removed, while the palm to the far right has.

Around here this is known as a palm tree. But the trunk is different from the ones at palm tree. Is it a different species? Bubba73 ^{You talkin' to me?} 04:58, 12 April 2015 (UTC)

'Palm tree' is used in a botanical and non-botanical way to mean a tree that looks like any one of the members of the Arecaceae (also called Palmaceae). The members of this family are variable in appearance depending on their genus. Many have long fronds, but some have fan-shaped fronds, as seen in your photograph. The trunks also vary from clean and shiny green to the way the plant appears in your image. It is difficult to identify that particular plant but I would suggest it is possibly either a member of the Chamaerops, Trachycarpus or possibly Brahea genera. Richard Avery (talk) 07:18, 12 April 2015 (UTC)

Thank you. I wanted to use the photo in some article, so Arecaceae would be safe. Bubba73 ^{You talkin' to me?} 13:23, 12 April 2015 (UTC)

It certainly would. Richard Avery (talk) 13:27, 12 April 2015 (UTC)

Looks like it might be a Sabal palmetto which is native to the area, but I'm not a botanist that is familiar with them and there are many different fan palms. --Modocc (talk) 15:05, 12 April 2015 (UTC)

I think you are probably right. I added a photo above from that article about its boots being removed, so it must be common for them to be removed. That threw me. Bubba73 ^{You talkin' to me?} 18:49, 12 April 2015 (UTC)

Resolved

Bubba73 ^{You talkin' to me?} 22:28, 12 April 2015 (UTC)

Why do your ears pop when you go over a hill in the car, but not when you go up several stories in an elevator?

Why do your ears pop when you go over a hill in the car, but not when you go up several stories in an elevator?

It depends how high the elevator goes. The Taipei 101 elevator has cabin pressure control to help passengers adapt to the pressure changes.--Shantavira|^{feed me} 12:41, 12 April 2015 (UTC)

If you move slowly (and the fastest elevator only has a speed of 45 mph), your ears won't pop, they will adapt to the environment. The change in air pressure is not high enough to make your ears pop. You need to move fast enough through a difference in altitude of 500 feet at least. Link: [1] "Popping of the ears is completely normal and usually occurs every 500 to 1,000 ft."--Llaanngg (talk) 12:47, 12 April 2015 (UTC)

I recall going up the elevators in various skyscrapers at various times in the past, and ear-popping seemed to be the norm. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:49, 12 April 2015 (UTC)

Yes, pressure differences in the ear even out on their own, given time. It's only rapid pressure changes that can't be accommodated without "popping". StuRat (talk) 19:52, 12 April 2015 (UTC)

This insightful question brought to you by — Preceding unsigned comment added by Deanwinchesterismaiwaifu (talk • contribs)

The question is based on a false premise. μηδείς (talk) 23:49, 12 April 2015 (UTC)

Effect of cold on human body

Can healthy humans get sick when exposed to a cold environment for a short (minutes) amount of time? I mean less than what would get us frostbite or a heart attack, but more than what is considered comfortable. --Llaanngg (talk) 12:40, 12 April 2015 (UTC)

Short answer: no. You get sick as a result of germs - in the case of the common cold, it's various viruses such as the rhinovirus or the coronavirus. Matt Deres (talk) 13:15, 12 April 2015 (UTC)

Some fools sturdy people enjoy exposing themselves to low temperatures with no harm suffered, apparently. Richard Avery (talk) 13:24, 12 April 2015 (UTC)

Yes, you need some contact with germs. But, could there be a link between being exposed to cold and the immune system? Couldn't it be that our defenses are lower when it's cold? Chemical processes are slower when it's cold, so it won't be a crazy idea.--Llaanngg (talk) 13:30, 12 April 2015 (UTC)

No, it's not crazy - that is where the name "cold" came from, after all. Check out the references in that section I linked to: the short answer is still "no", but the long answer is "kind of, but it's difficult to be sure". The correlation between being cold and catching sick is elusive when experiments are done, yet makes plain sense and seemingly plays out every winter season. It's probably a complicated mix of social and physiological factors, of which being chilly is only a tiny aspect. In cold and wet weather, people tend to stay indoors, away from fresh air and sunlight, which also makes them tend to congregate. This close proximity allows for easier transmission - as any parent of a school-age kid can attest, September is the month every school turns into a virus factory. Matt Deres (talk) 13:46, 12 April 2015 (UTC)

September? Don't think so. It's starting now (well when children go back to school) and will usually peak around June or July [2] I believe. Anyway there is a point here. While both hemispheres seem to have similar seasonal variations in temperate areas, tropical and sub-tropical countries also seem to have them albeit less defined. (See e.g. flu season.) Temperatures there are cooler during certain times such as the rainy seasons which also I think tends to be when flu and cold peaks, but depending on the place, they wouldn't be considered cold for people used to temperate climates and don't usually require heating or sufficient clothing. I mean the could be above the average you get in summer months in a number of places (consider reports of this cold snap in Malaysia [3]). So with the exception perhaps of those who get soaked by the rain, I'm not sure how much of a factor the cooler temperatures are likely to play (unless the problem is that the other temperatures are just too hot or it's adapting to the temperature change that is a problem). OTOH the seasons are less defined. This could indicate temperature plays a more important role, or it could be because of difference in behaviour. Day length doesn't vary so much. Most people won't want to be out in the wet weather, but depending on place, it doesn't necessarily rain all day, instead intense showers may be more the norm. And of course the cooler temperatures are often more conducive to outdoor activities. Nil Einne (talk) 14:34, 12 April 2015 (UTC)

Vitamin D levels and also the direct effects of UV radiation may also play a role. Count Iblis (talk) 15:34, 12 April 2015 (UTC)

Also, a big factor here is that in the Modern World where everyone has a central heating system at home and takes warm showers every day, people don't acclimatize to the colder weather outside in Winter. When you go outside, the body will shut down the blood flow to your hands and face even though that's not necessary. Exposing yourself to cold weather by going outside wearing only light clothing for ten minutes every day can help to reduce these effecs. Also taking cold showers every day is good way to prevent problems. Count Iblis (talk) 15:56, 12 April 2015 (UTC)

As usual people are replying here with what they "know" without checking the latest research. According to a study published in January this year "Exposure to a rhinovirus is still a prerequisite for catching a cold. But once a few viruses have entered cells of the nasal cavity inhaling cold winter air exposes those cells to the chill 'that the virus likes to replicate' and causes the immune system to respond less aggressively"[4]. So yes, cold can have an effect but I suspect the exposure would need to be longer than a few minutes. Richerman (talk) 16:10, 12 April 2015 (UTC)

That's definitely useful although only relates to one virus. But I don't think anyone has denied cold temperatures are a factor, simply that it's completely unclear how much, and why. (The latest research is as I said useful, but it doesn't really change the answer. We still don't know how much temperatures are a factor and why. There are already a number of reasons why cold temperatures could be a factor as discussed in the sources provided by earlier respondents, but we don't know how significant these actual are.) Nil Einne (talk) 13:23, 13 April 2015 (UTC)

You can get a cold any time of the year, for sure. Anecdotally, factors seem to include lowered resistance due to working too many hours with not enough sleep and/or increased exposure from going to some large public gathering place where viruses run rampant. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:47, 12 April 2015 (UTC)

Some additional ways cold can help viruses spread:

1) Cold, dry weather causes chapped, cracked lips, which provides an entrance point for viruses.

2) Coming into a warm, moist building from the cold causes the nose to run. If poor hygiene is practised (which is quite likely for kids), then the virus-containing snot ends up where others can contact it. StuRat (talk) 16:52, 12 April 2015 (UTC)

Not everybody gets chapped cracked lips nor do their noses run because of cold weather (−30 °C (−22 °F). I've been going in and out every hour for the last 9 hours and my nose hasn't run once. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 10:29, 13 April 2015 (UTC)

I sure get chapped, cracked lips, and feet too, if I don't use lip balm and moisturizer on my feet. And my nose runs constantly when shoveling snow. You seem to be better adapted to the cold than I. StuRat (talk) 06:03, 16 April 2015 (UTC)

Also plenty of places have winters that aren't particularly dry, and in fact summers that tend to be much dryer but still have strong seasonal flu and colds. Nil Einne (talk) 13:23, 13 April 2015 (UTC)

Related question

Do seasonal flu and colds show the opposite pattern in areas where it is very hot? For example, from experience I know that in Phoenix, Arizona people actually spend more time indoors during the summer than in the winter. Do more people get sick with cold and flu in summertime there? Deli nk (talk) 18:31, 13 April 2015 (UTC)

@Deli nk: You may want to just ask a new question. In my experience, follow-on questions often get glossed over. SemanticMantis (talk) 14:30, 14 April 2015 (UTC)

Earth's magnetic field

I understand that the earth's field is created by an electric current inside. But what causes the molten mass in the earth to have electric charge? I mean, where did the charge come from in the first place?--BoldEditor (talk) 13:12, 12 April 2015 (UTC)

We have an article at Earth's magnetic field that attempts to answer that; check out the section I linked to and see if that helps you. Matt Deres (talk) 13:17, 12 April 2015 (UTC)

My understanding is that a dynamo (generator) can function without a fixed permanent magnet, if you use the electrical output of the dynamo to power an electromagnet where the permanent magnet would be. How the current gets started in the first place, that I'm a little foggy about. Wnt (talk) 15:40, 12 April 2015 (UTC)

For smaller (automotive) dynamos, the residual magnetism of the stator provides sufficient current to start generation - the field coils are traditionally "flashed" seven times with a battery to provide the initial magnetism. Larger (industrial) dynamos usually had a separate permanent-magnet exciter to provide the field current. See Excitation (magnetic). Tevildo (talk) 20:49, 12 April 2015 (UTC)

The article dynamo theory summarizes current understandings of geomagnetic field production. Needless to say, the theory has some incomplete bits: numerical models sometimes conflict with actual observation.

Here are some important reading materials:

• Dynamo theory and paleomagnetism (1994)
• Numerical modeling of the geodynamo: Mechanisms of field generation and equilibration (1999)

This is an active area of research, so even some of our best answers aren't widely accepted or well-supported by theory and observational data. Nimur (talk) 16:45, 12 April 2015 (UTC)