Why can't water kill people, but people can be killed by diving?

On the surface, this problem seems to be a physical problem that needs reasoning and calculation. But people with rich life experience will think this is a very stupid question. Why do you say that? I'll tell you a joke, which many people may have heard. The story goes like this: once upon a time, a man wanted to increase his knowledge, so he joined a doctoral group. After he joined the group, someone asked a question: Will a drop of water die if it falls from a very high place? This person suspected that he might be in the wrong group, but later this issue caused a heated discussion, and various professional titles and doctors from famous universities began a heated discussion. The formula, the calculation of resistance and various assumptions were debated for a whole hour.

Of course, this is just a joke, but it tells us the answer very clearly. How high can a drop of water fall? The answer is that it can't be killed. But some people don't want to draw a conclusion that no matter how high the water is, it won't kill people. But if it turns into hail in autumn, isn't that another result?

Before changing the problem, we must first find out why raindrops fall from such a high sky but can't kill people. According to the commonly used force analysis method in physics, if an object falls from a height and ignores the air resistance, it will always accelerate its fall under the action of gravity. In this way, a drop of water fell to the ground at a high speed. But the fact is just like the joke above, we are all wet by the rain, and the speed of raindrops is not great.

The problem lies in air resistance. When analyzing problems, air resistance can't be ignored. So when raindrops actually fall, they will eventually fall at a constant speed due to the balance of air resistance and gravity.

Maybe someone will learn to use it now. Haven't you seen hail? Hail never kills people. But were you really hit by hail? Compared with raindrops, hail is stronger, bigger and exaggerated to the size of an apple. When the hail falls, the air resistance can not be ignored. If it falls from the sky and hits your head, it will knock you unconscious.

Many people think that coins, a metal product, will definitely kill people. As long as you are tall enough, is this really the case? Will coins hurt or kill people? When a coin falls, gravity will accelerate it, but it will also be affected by air resistance. So as long as we know how fast the coin will arrive under the balance of resistance and gravity, we can calculate the impact force at the moment of landing, and then judge its strength.

Scientists have long thought of this problem. Physicist Louis Broomfield once did an experiment of throwing coins from the sky, just to let the coins hit him. He made a flying machine and dropped coins from a height of 30 meters, but none of them hit him. After many attempts, he was finally hit, and a coin hit his chin. But guess what the result is? He is conscious, or his consciousness tells him that it doesn't hurt at all! According to his experimental results, even if you climb a skyscraper hundreds of meters high and throw it out, the falling speed of the coin will not increase much, and even if you are hit, it will not do much harm.