Science Questions Threak

Originally Posted by sonick

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Fuckin' magnets, how do they work?

Same with a Thermos:
you put hot in, it stays hot;
you put cold in, it stays cold.

How does it know?

Originally Posted by why

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So a person running in Denver will cool off from sweat more than in Louisiana (assuming all else is equal besides atmospheric pressure)?

As a side question, how is entropy usually calculated?

First question don't know. I guess you're asking how atmospheric pressure relates to how readily sweat evaporates. Obviously boiling occurs more readily because it takes less energy to have vapor pressure = atmospheric pressure, but the surface interaction of evaporation I guess could be different. I don't have the energy to research it.

Second question - entropy is defined by the number of ways you can arrange particles and has units J/K (energy/temp). Anyway you can calculate it

S = kBlnW

where W is the number of ways you can arrange the N particles in ni different bins subject to certain constraints on energy. kB is the Boltzmann constant which is the ideal gas constant divided by avogadro's number 6.02 x 10^23.

Now a simple way to show how entropy relates to the expansion of a gas (I am going quickly b/c I want to play some tennis before my gf gets home @ 7) -

You have volume(1) divided into n(1) bins. Each bin is of volume V. So V(1) = n(1)V. Your second volume is V(2), which has n(2) bins of volume V (V is the same for each of these V(1) and V(2)) so V(2) = n(2)V.

In the initial system you can put one molecule in it n(1) ways. Two molecules n(1)^2 ways and so on. For a mole you'd have n(1)^A ways (I'm calling avogadro's number A). The second volume, for 1 mole of gas, you'd have n(2)^A ways of arranging the equivalent molecules. So

∆S = kBln(n(2)^A) - kBln(n(1)^A)
= kBln((n(2)/n(1))^A)

- remember lnx^n = nlnx -

= AkBln(n(2)/n(1))

- remember AkB = R (gas constant)
- remember n(1) is just V/V(1)

= Rln(V(2)/V(1))

So, if volume increases, entropy increases. This effect is huge when changing states.

I have borrowed liberally from van Holde/Johnson/Ho's Principles of Physical Biochemistry. I have other textbooks that are clearer, but I just moved and can't find them.

Originally Posted by tagutcow

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Because the wind blows away the body heat that surrounds us.

Geez, I suck at science and even I know this ****.

sort of.

sweat cools us down by evaporating water, which releases heat to our surroundings. With no convection, the air close to our skin becomes saturated with water so the sweat can't evaporate, so we don't cool down.

the wind enables the sweat to evaporate by replacing the saturated air.

as well as just moving away the warm air next to our skin.


It's why 100% humidity makes us feel so hot, the sweat can't evaporate.

Originally Posted by holymadness

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When the temperature of the air is >37°, however, it ceases to cool the body.

this is wrong.

the evaporation of sweat is the main mechanism for losing heat, and this can be achieved even with temperatures above 37°

Originally Posted by hendrix

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sort of.

sweat cools us down by evaporating water, which releases heat to our surroundings. With no convection, the air close to our skin becomes saturated with water so the sweat can't evaporate, so we don't cool down.

the wind enables the sweat to evaporate by replacing the saturated air.

as well as just moving away the warm air next to our skin.


It's why 100% humidity makes us feel so hot, the sweat can't evaporate.

I'm willing to let the evaporative vs convective issue go, but the bolded is wrong. Evaporation requires heat. In fact it requires a ton of heat. It does not release it.

Originally Posted by CunningSmeagol

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I'm willing to let the evaporative vs convective issue go, but the bolded is wrong. Evaporation requires heat. In fact it requires a ton of heat. It does not release it.

That heat comes from our body -> cool down.

Originally Posted by Dakota rube

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Same with a Thermos: you put hot in, it stays hot; you put cold in, it stays cold. How does it know?
It doesn't. All it does is prevents heat transfer by removing anything that enables it, thus creating a partial vacuum. Think of it as a bottle inside of a bottle with all the air sucked out in between. That takes cares of convection and conduction and I think they are caoted for 'radiation type' heat transfer.

Originally Posted by onix

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That heat comes from our body -> cool down.

Is this supposed to explain something?

Originally Posted by CunningSmeagol

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See? Convection. It's like if you were in cold water and a strong current ripped your wetsuit off.


Then what does the strong current do? Will it call the next morning? I hope I at least get dinner out of it.

Originally Posted by Agnacious

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Then what does the strong current do? Will it call the next morning? I hope I at least get dinner out of it.

Goes in your out mouth if you're lucky.

Originally Posted by edinatlanta

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If "evolution" is correct, why is there God?

The theory of natural selection (evolution) does not account for a "why". Your question isn't really a science one, it would seem.

do animals enjoy sex as much as humans do?

Originally Posted by CunningSmeagol

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I'm willing to let the evaporative vs convective issue go, but the bolded is wrong. Evaporation requires heat. In fact it requires a ton of heat. It does not release it.

sorry you're absolutely right.

the evaporation process uses heat from our bodies to...evaporate.

terrible mistake there.

Originally Posted by acidboy

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do animals enjoy sex as much as humans do?

No, the only animal besides human that enjoy sex like human is dolphins (I think all whale family).