Physicists use experiments to tell you how to quickly cool hot coffee.

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According to foreign media reports, how does the temperature of hot coffee change? How can we make the coffee cool quickly? A few days ago, a physicist had nothing to do to study this problem by laboratory method. And the whole experiment was published in Wired magazine.

Like many people, I also like to enjoy a good cup of coffee in my spare time. Not such as Lafayette, Fat-free Coffee or Vanilla Coffee, but a cup of hot traditional classic black coffee. But there is often a problem with hot coffee-it is too hot to be imported immediately. When we get a cup of hot coffee, we must find the best way to cool it down so that we can taste it quickly.

At present, I have two more ways to cool hot coffee. One is to open the lid of the coffee cup, the other is not to open the lid, but I will blow through the drinking hole in the coffee cup so that it can cool down.

Which method is the best? Let's try it through a simple physics experiment. Before that, I need some tools. First of all, there is no doubt that it is a coffee cup; second, we need some thermometers. What's the temperature of the hot coffee? I think 80 degrees Celsius is the most common hot coffee temperature. And what kind of temperature is suitable for drinking coffee? In my personal experience, 64 degrees Celsius is a pretty good choice.

Now let's do an experiment. First of all, I will simulate the hot water of black coffee into three cups of coffee.

Now we have three cups of hot coffee with a temperature of 80 degrees Celsius. Cup 1 has a lid, which is our standard coffee cup, while Cup 2 has no lid, and Cup 3 has a lid, but I keep blowing air into it through a small hole.

So which cooling method works better? Of course, I can taste each cup and compare it with my own feelings. But I will actually measure the temperature with a thermometer and put a temperature probe in the three cups.

In order to make the third cup as realistic as possible, I will blow air into it through the small hole. Not continuously, but at intervals, as if I was busy doing something else while waiting for the coffee to cool down. We collect temperature data through temperature sensors. Here are the values of three coffee cups that vary with temperature in a few minutes.

(the X axis is the time in seconds and the Y axis is the temperature. The blue line represents the temperature curve of cup 1 with time, the green line represents the temperature curve of cup 3 with time, and the yellow line represents the temperature curve of cup 2 with time. )

You can see the results of the experiment. Although the starting temperature is different, the cup without a lid obviously cools the fastest. Because in essence, we only have two ways to cool the coffee. First of all, we use heat conduction to lower the temperature of the coffee by placing the hot coffee next to the colder object to transfer the heat to the colder object. In my experiment, what is colder than coffee is the air and the base of the cup. This is not enough to have a significant effect on the temperature of coffee.

The second method is through evaporative cooling. When the water on the surface of the coffee evaporates, it will leave water molecules with lower heat energy, resulting in a decrease in the temperature of the coffee. Without the lid, the steaming area of the coffee in the cup increases, so it can cool quickly. If there is a lid, we can increase the evaporation rate by blowing air into the hole, but this is obviously not as effective as lifting the lid.

Now let's do another experiment. Insert a cup stopper into the drinking hole to see if it helps to keep the coffee warm.

I still repeated the early experiment with two cups. Cup 1 has a lid, while Cup 2 has a lid and a cup stopper. Here are the changes in the temperature of two cups of coffee over time:

(the X axis is the time in seconds and the Y axis is the temperature. The blue line represents the temperature curve of cup 1 with time, and the yellow line represents the temperature curve of cup 3 with time. )

The thermometer shows that the temperature of the two cups of coffee is about the same. I thought coffee without a stopper would cool faster. But this is not the case. It seems that the main function of the cup stopper is to prevent coffee from spilling. one