How does skin pigmentatoon affect rate at which a body cools down?

Also how does the body temp at TOD affect rate at which a body cools down?

I don't know what TOD stands for, but if this is a biology Q with "body" meaning e.g. human body rather than a physics Q where "body" means an object, the answer would be as follows (although the two possibilities above will overlap somewhat).

People with darker skins (like myself! - [I have a golden complexion - sorry have to brag occasionally!! $] have a greater amount of melanin in the epidermis - as in physics, a darker "body" tends to [first in general]:-
a) reflect less heat [and light],
b) absorb more heat, and
c) radiate less heat [CALLING ANY PHYSICS NERD: please correct me on this last bit [radiation] if I am talking bovine faeces].

Since a body losing more heat is equivalent to it gaining less heat (because the final temperature will be the net effect), the answer to your Q includes (in the same order) [when external temp is high]:
a) a darker body will cool down slower
b) will heat up quicker
c) will cool slower [PHYSICS NERD again???].

(This is completely in contrast to my own experience (I can have a boiling shower [where white people scream and go crimson red], but I do not like Scottish/Canadian weather) - I can't explain this discrepancy!)

M (specialist biology tutor)

(edited 5 years ago)

Reply 2

username3249896

12

Original post by macpatgh-Sheldon

c) radiate less heat [CALLING ANY PHYSICS NERD: please correct me on this last bit [radiation] if I am talking bovine faeces].

c) will cool slower [PHYSICS NERD again???].

Black surfaces are good emitters of radiation and in fact radiate more heat and cool faster
https://www.quora.com/Black-bodies-radiate-the-most-heat-and-reflect-the-least-light-while-white-radiates-the-least-heat-and-reflects-the-most-light-Whats-the-reason-for-this

Good emitters are good absorbers. The reason is explored below. Basically, the process of absorbing an incoming photon is exactly the reverse of the process of emitting one.
https://physics.stackexchange.com/questions/159856/why-is-black-the-best-emitter

Consequently, black surface will cool faster.
https://answers.yahoo.com/question/index?qid=20110223052738AAyduZg
https://www.physlink.com/education/askexperts/ae136.cfm

Reply 3

nexttime

22

TOD seems to be time of death? In which case for both questions I can't imagine skin pigmentation makes any kind of significant difference considering that when most people die they are wearing clothes! Even if they were quite unclothed, surely factors like body surface area to volume ratio (including the position of the body), ambient temperature, and whether they were wet or dry will make far, far more difference.

But in theory, yes black radiates more heat to maybe it could make a tiny tiny difference.

Original post by BobbJo

Black surfaces are good emitters of radiation and in fact radiate more heat and cool faster
https://www.quora.com/Black-bodies-radiate-the-most-heat-and-reflect-the-least-light-while-white-radiates-the-least-heat-and-reflects-the-most-light-Whats-the-reason-for-this

Good emitters are good absorbers. The reason is explored below. Basically, the process of absorbing an incoming photon is exactly the reverse of the process of emitting one.
https://physics.stackexchange.com/questions/159856/why-is-black-the-best-emitter

Consequently, black surface will cool faster.
https://answers.yahoo.com/question/index?qid=20110223052738AAyduZg
https://www.physlink.com/education/askexperts/ae136.cfm

I don't know why you say "consequently". The second point correctly observes that black surfaces absorb radiation well, and as we are generally being struck by a very powerful radiation source (outside at least), surely the conclusion needs to be 'it depends on temperature of the body, temperature of the surroundings and the strength of the sun'?

But thanks for trying to source your answer, even if most of the citations are just other fora :smile:

Reply 4

username3249896

12

Original post by nexttime

I don't know why you say "consequently". The second point correctly observes that black surfaces absorb radiation well, and as we are generally being struck by a very powerful radiation source (outside at least), surely the conclusion needs to be 'it depends on temperature of the body, temperature of the surroundings and the strength of the sun'?

But thanks for trying to source your answer, even if most of the citations are just other fora :smile:

It also depends on emissivity on the body.

If it "depends on temperature of the body, temperature of the surroundings and the strength of the sun" only, then black surface and white surface at the same temperature cool at the same rate. But this is not the case, as proven experimentally. So there is another factor which is called emissivity which affects cooling

The citations are just more detailed explanations. Sorry to use other fora. It is what googling gave.

It is true that heat loss by radiation is a small contribution. This is why biological organisms have other mechanisms to assist heat loss. e.g Humans have sweating, vasodilation, hairs and other.

How does skin pigmentatoon affect rate at which a body cools down?

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