Question on Heat Transfer and sweating

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Kaelyn327
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#1
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#1
So this is a question from a past paper --
Suggest why a runner might cool down too quickly if he does not wear a foil sheet.

And the mark scheme says:
1. (still covered in) sweat / evaporation mentioned;
2. not generating as much "new" heat

But I literally don't get why the mark scheme says so.
Does the first point genuinely mean that the runner keeps sweating?
But what I think is that the runner would be covered in sweat no matter what. Even if he does wear a foil sheet he will still be covered in sweat but the sweat cannot evaporate.
I don't understand the second point either. Can someone elaborate it for me please?
Does that mean if the runner wears a foil sheet, his body will generate more "new" heat?
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Callicious
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#2
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#2
I'm curious as to who wears a foil sheet while running. I've never seen anyone running down the street wearing a foil sheet :_:

Either way, from my standpoint, the idea that the runner wont generate new heat while wearing the sheet or not wearing it is ludicrous. He's running, he will be metabolising sugars and his bodies energy stores, and in turn he is going to be generating heat. If he doesn't wear a foil sheet, there wont be anything to prevent the heat from escaping, and in turn all the heat he generates should be lost by the evaporation by the sweat on his brow. Or her brow. I just say his by default, #sexismconfirmed. Either way, the foil sheet, as shown here on his brow...
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will result in the reflection of the radiation from his body back at himself. Which is nice and all, but er, I can say that from running in the cold, you don't want that: you will heat up like a potato. Another thing to note is that although he wont be generating as much heat if he is cooler, he will still be generating a considerable sum, a negligible difference. That question makes literally no sense to me.
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Kaelyn327
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#3
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#3
(Original post by Callicious)
I'm curious as to who wears a foil sheet while running. I've never seen anyone running down the street wearing a foil sheet :_:

Either way, from my standpoint, the idea that the runner wont generate new heat while wearing the sheet or not wearing it is ludicrous. He's running, he will be metabolising sugars and his bodies energy stores, and in turn he is going to be generating heat. If he doesn't wear a foil sheet, there wont be anything to prevent the heat from escaping, and in turn all the heat he generates should be lost by the evaporation by the sweat on his brow. Or her brow. I just say his by default, #sexismconfirmed. Either way, the foil sheet, as shown here on his brow...
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will result in the reflection of the radiation from his body back at himself. Which is nice and all, but er, I can say that from running in the cold, you don't want that: you will heat up like a potato. Another thing to note is that although he wont be generating as much heat if he is cooler, he will still be generating a considerable sum, a negligible difference. That question makes literally no sense to me.
I still don't understand what the mark scheme says. But if it wasn't the mark scheme I would literally write something like there won't be anything to stop him from sweating if he doesn't wear a foil sheet so as he sweats he cools down quickly. So I totally agree with your point that "If he doesn't wear a foil sheet, there wont be anything to prevent the heat from escaping, and in turn all the heat he generates should be lost by the evaporation by the sweat".

But I just don't get why it says "not generating as much 'new' heat" in the mark scheme.
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Callicious
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#4
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#4
(Original post by Kaelyn327)
I still don't understand what the mark scheme says. But if it wasn't the mark scheme I would literally write something like there won't be anything to stop him from sweating if he doesn't wear a foil sheet so as he sweats he cools down quickly. So I totally agree with your point that "If he doesn't wear a foil sheet, there wont be anything to prevent the heat from escaping, and in turn all the heat he generates should be lost by the evaporation by the sweat".

But I just don't get why it says "not generating as much 'new' heat" in the mark scheme.
I'd say ignore it. It's ridiculous. The way the body generates heat when cold is generally through muscle twitching/etc, and while running, that is going to be negligible in comparison to the heat from the metabolic activity for the guy to keep up his pace.

The foil wont change the fact he is running and generating heat, hence the MS is stupid.
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artful_lounger
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#5
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#5
I would presume, not having seen the question, is that it refers to the practice of runners wearing a foil blanket after completing a race.

The foil would prevent the heat carrying sweat from evaporating into the atmosphere, and would create a sort of "micro-climate" under the foil of a warm and humid environment. This would dissipate over time as it's not a sealed environment but it would do so more slowly than if it were not there at all, creating a slower cooling process.

For the second point, it may be referencing the fact that while running, a large amount of heat is being generated by the movements of the muscles; after the race, while the runner is sitting, chilling under their foil with some water, they are no longer moving nearly as much as they had been and thus this "source" of heat is no longer in play, and it's just their baseline metabolism.

It seems rather poorly worded and a bit of a leap of logic which assumes more than a physics curriculum...
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AHappyStudent
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#6
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#6
I think that it means wearing the foil blanket after finishing the race.

While he is running, he is sweating to cool him down quickly an running is keeping warming him up. These two processes keep him at a constant temperature as they act in opposite 'directions'

When he stops running, he is no longer heating himself up with muscle movement but the sweat on his skin still keeps cooling him down. Without the foil blanket, he might cool down too quickly. The foil blanket reduces the rate at which he cools down.

Not sure if this is right but it's my guess
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Callicious
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#7
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#7
(Original post by artful_lounger)
I would presume, not having seen the question, is that it refers to the practice of runners wearing a foil blanket after completing a race.

The foil would prevent the heat carrying sweat from evaporating into the atmosphere, and would create a sort of "micro-climate" under the foil of a warm and humid environment. This would dissipate over time as it's not a sealed environment but it would do so more slowly than if it were not there at all, creating a slower cooling process.

For the second point, it may be referencing the fact that while running, a large amount of heat is being generated by the movements of the muscles; after the race, while the runner is sitting, chilling under their foil with some water, they are no longer moving nearly as much as they had been and thus this "source" of heat is no longer in play, and it's just their baseline metabolism.

It seems rather poorly worded and a bit of a leap of logic which assumes more than a physics curriculum...
(Original post by AHappyStudent)
I think that it means wearing the foil blanket after finishing the race.

While he is running, he is sweating to cool him down quickly an running is keeping warming him up. These two processes keep him at a constant temperature as they act in opposite 'directions'

When he stops running, he is no longer heating himself up with muscle movement but the sweat on his skin still keeps cooling him down. Without the foil blanket, he might cool down too quickly. The foil blanket reduces the rate at which he cools down.

Not sure if this is right but it's my guess
That seems like the most likely case. Let's hope the OP can find out from his/her teacher
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Kyx
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#8
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#8
(Original post by Kaelyn327)
So this is a question from a past paper --
Suggest why a runner might cool down too quickly if he does not wear a foil sheet.

And the mark scheme says:
1. (still covered in) sweat / evaporation mentioned;
2. not generating as much "new" heat

But I literally don't get why the mark scheme says so.
Does the first point genuinely mean that the runner keeps sweating?
But what I think is that the runner would be covered in sweat no matter what. Even if he does wear a foil sheet he will still be covered in sweat but the sweat cannot evaporate.
I don't understand the second point either. Can someone elaborate it for me please?
Does that mean if the runner wears a foil sheet, his body will generate more "new" heat?
The fact that the mark scheme says 'still' covered in sweat suggest the question might be about the runner AFTER the race, as previous posters have suggested


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Kaelyn327
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#9
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#9
So what the first point in the mark scheme is meant to state the fact that the runner will still be sweating after he's done the race and the second point is saying that the runner won't be generating as much heat as he does when he's still running?
I'm trying to think in a way that even though the question is asking "why... cool down too quickly without the foil sheet" there's nothing to do with comparing "with" and "without" foil sheet.
Am I right?
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Kyx
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#10
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#10
(Original post by Kaelyn327)
So what the first point in the mark scheme is meant to state the fact that the runner will still be sweating after he's done the race and the second point is saying that the runner won't be generating as much heat as he does when he's still running?
I'm trying to think in a way that even though the question is asking "why... cool down too quickly without the foil sheet" there's nothing to do with comparing "with" and "without" foil sheet.
Am I right?
With the foil sheet, the thermal energy released by the runner's body can be reflected back. Without the foil sheet, it can't.


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Kaelyn327
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#11
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#11
(Original post by Kyx)
With the foil sheet, the thermal energy released by the runner's body can be reflected back. Without the foil sheet, it can't.


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Yea, I know this bit but I just don't get why "not generating as much new heat".
I'm super confused😟😟😟
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Kyx
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#12
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#12
(Original post by Kaelyn327)
Yea, I know this bit but I just don't get why "not generating as much new heat".
I'm super confused😟😟😟
Idk


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AHappyStudent
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#13
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#13
The runner is running he is heating up due to rapid muscle contractions. When he stops running, he is no longer heating himself with muscle contractions so 'no new heat'. I don't think that the mark scheme is well worded but I understand what it is getting at
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Kyx
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#14
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#14
(Original post by AHappyStudent)
The runner is running he is heating up due to rapid muscle contractions. When he stops running, he is no longer heating himself with muscle contractions so 'no new heat'. I don't think that the mark scheme is well worded but I understand what it is getting at
I realised it just as a saw there was a new post in this thread


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Joinedup
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#15
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#15
(Original post by Kaelyn327)
Yea, I know this bit but I just don't get why "not generating as much new heat".
I'm super confused😟😟😟
while the runner is running there's a process putting heat into his/her body at an unusually high rate and a process removing heat from his/her body to the environment at an unusually high rate.. body temperature is regulated at a healthy level

when the runner stops running abruptly, the process putting the unusual amount of heat into their body stops abruptly too but there is a delay before the process removing heat from their body stops. there is a risk that the body temperature can fall to an unhealthy level in the period immediately after stopping running.

markschemes show possible acceptable answers but are not model answers that you're supposed to remember and copy.
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Kaelyn327
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#16
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#16
(Original post by AHappyStudent)
The runner is running he is heating up due to rapid muscle contractions. When he stops running, he is no longer heating himself with muscle contractions so 'no new heat'. I don't think that the mark scheme is well worded but I understand what it is getting at
I guess I'm getting there...
So basically the question has nothing to do with comparing wearing and not wearing the foil sheet. You are just asked to say why the runner cools down after the race, i.e. compare "what's happening" to his body during and after the race, but not with and without the foil.
So first you have to mention something related to sweat and evaporation as the runner is STILL sweating after he's done running. That's why it says runner STILL covered in sweat in the mark scheme.
And for the second point, what the mark scheme suggests "not generating as much 'new' heat" simply means after the race the runner won't be generating as much heat as he does while he's running. So again there's nothing to do with comparing whether he's wearing the foil sheet or not. It's all about comparing "what's happening" to his body during and after his running.
Am I making any sense here? Is that what the mark scheme means?

Also, one more quick question. I know you don't have to stick to everything in the mark scheme all the time. And sometimes the mark scheme would suggest some other possible alternatives in the right-hand column. But for this question, nothing I wrote is in the mark scheme because I misunderstood what the question really wants and attempted to explain why the runner cools down more quickly if he doesn't wear the foil sheet than if he does, as opposed to what makes the runner cools down more quickly after his run. I wrote something like "there's nothing to stop his sweat from evaporating so as he sweats he cools down (more) quickly (than if he wears a foil sheet)", which has nothing to do with what the mark scheme suggests but I still think my answer is making sense. Do I still get the mark for this question? If I were the one setting the question, I would change the question to "Explain why the runner cools down too quickly AFTER HIS RUN, if he doesn't wear the foil sheet" coz I still think the question is a bit confusing anyway.
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Kaelyn327
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#17
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#17
You know in the mark scheme there's a column called Answers and a column called Notes listing some of the alternatives as well as what answers the marker should 'ignore". So hhat will the marker do if my answers aren't any of those columns? How will that be marked? Will the marker read through my answers and see if they are making sense or just ignore them?
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Kyx
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#18
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#18
(Original post by Kaelyn327)
You know in the mark scheme there's a column called Answers and a column called Notes listing some of the alternatives as well as what answers the marker should 'ignore". So hhat will the marker do if my answers aren't any of those columns? How will that be marked? Will the marker read through my answers and see if they are making sense or just ignore them?
Sometimes a student makes a valid point that the examiner's missed. In this situation the examiner will decide whether or not to give the mark.

If the examiner doesn't know if it is valid/whether to award the mark, there will be a discussion and the mark scheme could potentially be changed.


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Omar717
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#19
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#19
I think the question is saying that if there is no foil to insulate the runner, heat will be given off too quickly and the runner will cool down too fast. Since he has stopped running no new heat is generated to offset the heat being transferred to the surroundings. The evaporation of the sweat will cool him down, but this is prevented by the foil.

When running heat is transferred to and from the system, but when he stops it is only being transferred to surroundings. Heat is transferred to the body via work done by the muscles.

Correct me if I've made a mistake.

Edit: Also forgot to mention radiative heat transfer from the body which is blocked by the foil. The foil is shiny (low emissivity) meaning it is less likely to absorb the heat. A perfect emissivity (1.0) would be a blackbody which fully absorbs.
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