Or is it better to leave it on?

還是不要擦掉比較好？

Obviously we're ignoring all social norms and medical advice and just talking from a pure physics perspective.

顯然，我們在這會忽略所有的社會規範和醫學建議，只是從純粹的物理學角度來討論。

And in physics, there are two main ways you can use water alone to cool something down. 

在物理學中，有兩種​​主要方法可以單獨使用水來冷卻物體。

The first water cooling method is to run cool water over or through the hot object so the water warms up and takes away the heat, and therefore, cools the object down.

第一種水冷卻方法是將冷水流過或流過熱物體，使水升溫並帶走熱量，從而冷卻物體。

This direct transfer of heat is the basic idea behind the radiators in car engines, liquid cooling of fancy gaming computers, and water cooling of power plants.

這種直接的熱量傳遞是汽車引擎散熱器、高級遊戲電腦的液體冷卻和發電廠水冷卻背後的基本概念。

For a human being, this would mean drinking, say, a liter of freezing-cold water every hour, letting your body heat the water up to body temperature, and then removing it from your body by urinating or sweating and then wiping off the sweat.

對於人類來說，這意味著每小時喝一公升冰冷的水，讓身體將水加熱到體溫，然後透過排尿或出汗將其排出體外，然後擦掉汗水。

A liter of water can move 1 calorie of heat per degree Celsius it heats up, so using water for liquid cooling can remove at most around 37 Calories of heat every hour

一公升水每升溫攝氏度可帶走 1 卡路里的熱量，因此使用水進行液體冷卻每小時最多可帶走約 37 卡路里的熱量

One calorie for every degree Celsius between freezing and body temperature.

冰點到體溫之間每升高一攝氏度就消耗一卡路里熱量。

The second water cooling method is to put water on the object and let it evaporate.

第二種水冷卻方法是將水放在物體上並讓其蒸發。

A liter of water, to evaporate, absorbs around 540 calories of heat, which is a lot more than the 37 Calories removed by drinking and urinating ice water.

一公升水蒸發時會吸收約 540 卡路里的熱量，比飲用和排尿冰水吸收的 37 卡路里多得多。

But a human body can't necessarily evaporate a liter of water every hour: a square meter, under room temperature conditions, will only evaporate about a third of a liter per hour, and the surface area of a human is only between 1 and 2 square meters. 

但人體不一定每小時蒸發一公升水：一平方公尺，在室溫條件下，每小時只會蒸發約三分之一公升，而人體的表面積僅在 1 至 2 之間平方公尺。

So we could expect a sweaty human body to lose at most maybe 180-360 Calories of heat every hour from evaporative cooling.

因此，我們預計出汗的人體每小時最多會因蒸發冷卻而損失 180-360 卡路里的熱量。

Which is still 5 to 10 times more cooling power than liquid cooling.

其冷卻能力仍比液體冷卻高 5 至 10 倍。

Obviously, evaporation is also super condition-dependent: if it's hotter or windier or drier, then the power of evaporative cooling increases substantially, while if it's cooler or more humid then evaporation is less effective. 

顯然，蒸發也非常依賴條件：如果天氣更熱、風更大或更乾燥，那麼蒸發冷卻的能力就會大大增加，而如果天氣更冷或更潮濕，那麼蒸發的效果就會較差。

But either way, it seems pretty safe to say that for human bodies, evaporative cooling is far more effective than liquid cooling.

但無論哪種方式，似乎可以肯定地說，對於人體來說，蒸發冷卻比液體冷卻有效得多。

In other words, letting your sweat evaporate is far more effective than wiping it off.

換句話說，讓汗水蒸發遠比擦掉更有效。

Which actually isn't that surprising: sweating is our evolutionary means of cooling off, so perhaps it's not surprising that letting your body do its thing turns out to be a good idea, but it's amazing how effective it really is. 

這其實並不奇怪：出汗是我們進化而來的降溫方式，所以讓你的身體做它自己的事情被證明是一個好主意也許並不奇怪，但令人驚訝的是它的實際效果如何。

And luckily your body can use both methods of water cooling.

幸運的是，你的身體可以使用這兩種水冷卻方法。

If you drink cold water, you benefit from direct heat transfer while your body warms the water up to body temperature, and then you benefit from evaporative cooling when the water evaporates as sweat. 

如果你喝冷水，當你的身體將水加熱到體溫時，你會受益於直接熱傳遞，然後當水作為汗水蒸發時，你會受益於蒸發冷卻。

And physics doesn't completely prohibit wiping off your sweat.

物理學並沒有完全禁止擦汗。

If sweat is literally dripping off of you, a) it's not going to help evaporatively cool you once it's on the ground, and b) chances are you're producing sweat faster than it can evaporate.

如果汗水確實從你身上滴下來，a）一旦它落在地面上，它就不會幫助你蒸發冷卻，b）你產生汗水的速度可能比蒸發的速度快。

So it's probably ok to wipe some of the sweat off - or perhaps better yet, smear it around to make sure it has the most surface area possible for the most effective cooling!

因此，擦掉一些汗水可能就可以了，或者更好的是，將其塗抹在周圍，以確保其具有最大的表面積，從而實現最有效的冷卻！

As a reminder - nothing in this video constitutes medical or hygiene advice.

提醒一下：本影片中的任何內容均不構成醫療或衛生建議。

But if your sweat is dripping, it's much better – for the purposes of evaporative cooling – to smear it around rather than wipe it off entirely.

但如果你的汗水正在滴落，出於蒸發冷卻的目的，最好將其塗抹在周圍，而不是完全擦掉。

And if you're hot and sweaty but it's not dripping, physics says "leave it on."

如果你很熱、出汗，但它沒有滴下來，物理學會說「讓它繼續留著」。