BBC 6分钟英语学习 多少热量会从你的头上发散

English from BBC Learning

English. Hello. This is six minute English from BBC Learning English.

I'm Rob and I'm Georgina. What's freezing cold outside today?

Georgina, make sure you wrap

up warm. I'll put my woolly hat on.

When I was growing up, I was told that you lose half your body heat from your head.

Oh no, don't believe that. Your gina.

It's just a popular myth. You know something people think is true, which actually isn't, like bulls get angry when they see the color red, or goldfish only have a three 2nd memory.

Oh, I thought red really did make bulls angry.

But you're right. There is some disagreement over the age or question Should I wear a hat when it's cold outside?

In this program, we'll be asking how much body heat we lose from our head, and discovering that a simple answer isn't so easy to find.

But 1st, it's time for my quiz question.

And let's start by asking someone who knows all about surviving in the cold the US Army, according to the Cold Weather Survival Chapter of the US Army Field Guide, how much heat is lost in the cold through an uncovered head?

Is it A 30 to 35 %?

B 40 to 45 %, or C 50 to 55 %?

You might say it's just a popular mythrob, but I still think half your body heat is lost from the head, so I'll say, see, 50 to 55 %.

OK, georgina will come back to that later.

Anyway, whichever answer is correct, the US Army obviously thinks a large percentage of body heat escapes through the head, but that might not be the whole picture.

Over the years, experiments to measure body temperatures in the snowy wastelands of Canada and Alaska have given wildly different results, mostly because of variations in the methods used, e.g.

whether the volunteer's head was covered or not, and whether they were dry or submerged in water.

So maybe the US army's view is out of date.

And here's some surprising information that Tim Harford, presenter of BBC World Service Program, more or less found after a quick search on Google.

The head accounts for about 7% of the body surface area, and the heat loss is fairly proportional to the amount of skin that showing A human body s surface area means the total area of skin on its outer surfaces, that's a head, chest or tor so, plus the arms and legs.

According to this view, heat loss, meaning the total amount of heat transferred away from something through its surface is proportional to body surface area.

In that case, a 50% heat loss from the head, which only makes up 7% of the body's surface area.

Seems like an overestimation. In the 1950s, other military experiments were carried out in Canada on soldiers wearing Arctic warfare clothing, the kind of super warm thermal clothes you might wear in sub zero temperatures, but with nothing to cover their heads.

Here's professor of physiology Mike Tipton taking up the story with BBC World Service Program.

More or less, the question was, how important is the head now to also provide some equipment for some hat or some form of insulation?

And in that scenario, of course, when youve got insulation over much of the rest of the body, preventing heat loss, then obviously the percentage of heat lost from the head is going to be high.

And at minus four degrees Celsius, it amounted to about half of the resting heat production of the body.

Here, the soldiers bodies were protected with insulation, thick material used to stop heat from escaping.

Since their heads were exposed to the cold, around half of their body heat escaped that way when resting, not moving or doing anything active.

And so the idea that half your body heat is lost to the head slowly became a popular myth.

But before you throw your woolly hats in the bin, there's another consideration to bear in mind, one that concerns your core temperature, that's the internal temperature inside your body, including the blood, heart and other vital organs.

When the head is allowed to get cold and the body is well insulated, the body s core temperature dropped rapidly due to the circulation of blood.

Wow, this question really is blowing hot and cold.

Now, I have no idea how much heat is actually lost from the head.

Why don't you just tell me the answer?

Rob OK, then, well, in my quiz question, I asked how much heat the US Army guide says is lost through the head?

I guessed, see, 50 to 55 %, or roughly one half.

Was I right? Well, you were warm, georgina.

But not right. In fact, the Army field guide says, B 40 to 45 %.

But as we've seen in this case, cold facts are hard to come by.

Let's wake up our vocabulary, then, because we're still not sure

if wearing a hat to keep warm is just a popular myth, something people believe to be true, but which actually is not.

It seems that heat loss, the total of a heat

transferred away from something, is linked to the surface area, or total area, of the body's outer surfaces' when exposed to the cold.

But wearing installation material used to stop heat from escaping may change the body's resting temperature, its temperature were not moving and at rest, and also affect your core temperature, your body's internal temperature, including the heart and blood.

That's all for this programms. Remember to wrap up warm for the winter, and maybe Papa Willie hat in your pocket to wear just in case.

See you again soon. For more trending topics and vocabulary here at six minute English.

Bye for now. Bye.

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