If it is only used for traveling between cities and daily outdoor wear, 6000mm waterproof jackets and pants are enough to cope with it. But if you need to go to a more difficult environment, it is best to choose jackets and pants with a waterproof index of 10,000mm or more.
It is a common thing to encounter rain outdoors. For outdoor sports enthusiasts, a jacket with good waterproof function is a must-have equipment. The waterproof performance of a jacket is closely related to its waterproof index.
Let us briefly understand this index first. Their unit is millimeters of water column pressure. The usual explanation is that when a 10,000mm high water column presses on the fabric and no more than 3 drops of water seep out of the fabric within 24 hours, then we think The waterproof index of this dress is 10000mm.
So the following question arises, what is the difference between 3000mm, 6000mm waterproof pressure and 10000mm waterproof pressure? Which type of jacket should I buy? It goes without saying that the higher the waterproof index, the stronger the waterproof performance, and of course the higher the price. The key to choosing a jacket under certain specifications depends on your actual needs. The one that suits you is the best. If it is only used for inter-city travel and daily outdoor wear, a waterproof index of 3000mm to 5000mm is enough; if it is for quasi-professional outdoor hiking, camping or crossing activities, a jacket with a waterproof index of 6000mm to 8000mm is enough to cope with it; but if If you need to go to an environment with difficult natural conditions for professional mountaineering, adventure and other outdoor activities, it is best to choose jackets and pants with a waterproof index of 10000mm or above.
We often hear that – ah, the rainproof index of this jacket is 6000, and the rainproof index of that jacket is 10000. The units of 6000 and 10000 here are millimeters of water column pressure. The usual explanation is that when a 10,000mm high water column presses on the fabric and no more than 3 drops of water seep out of the fabric within 24 hours, then we consider the waterproof index of this piece of clothing to be 10,000mm. So someone asked, what is the difference between 6000mm waterproof pressure and 10000mm waterproof pressure? What kind of jacket should I buy? Wait for similar questions. Well, let’s start from the beginning.
The ending speed of raindrops
If there is no air (resistance), the clouds in the sky turn into rain and fall. After accelerating all the way, the speed when reaching the ground will reach 300 meters/second. This speed is basically equivalent to half the speed of a bullet. There would be no living creatures at all on land. Thank God, due to the existence of air resistance, when the raindrops form and start to fall, after a short period of variable acceleration (the acceleration gradually becomes smaller), when the air resistance encountered by the raindrops is equal to its own gravity, ok, at this time, the raindrops begin to move at a constant speed. Falling phase until reaching the ground. In physics, this uniform speed is called the closing speed of an object.
Raindrop size
Some people have concluded that under normal circumstances, the diameter of raindrops is between 0.5mm and 6mm. In rare cases, the diameter of raindrops can reach 8mm or even 10mm (observed in the Hawaiian Islands).
Scientists have discovered that if water particles are smaller than 0.5mm, then due to the effect of atmospheric updrafts, water particles of this size can be kept in the air. The size of raindrops generally does not exceed 6mm. Due to the existence of air resistance, large raindrops often break down into many small raindrops whose volume decreases sharply during the falling process. In addition, these large raindrops constantly collide with each other as they fall, causing them to fall apart. Scientists have found that under laboratory conditions, large raindrops usually begin to disintegrate when they reach about 5 millimeters in diameter. In clouds, when the diameter of large raindrops reaches 5 mm, they usually break up due to collision with each other. This is why it is rare to see raindrops with a diameter of 5 mm or more on the ground, because raindrops cannot avoid the fate of colliding with many others of their kind.
Raindrop size and ending speed
The ending speed of raindrops has a strong correlation with the size of the raindrops. Generally speaking, hairThe ending speed of drizzle (diameter 0.5mm) is 2 meters/second, while the ending speed of heavy rain (raindrop diameter about 5.5mm) is 8~9 meters/second.
Closing speed and water column height
With the closing speed, we can know the kinetic energy behind the raindrops. The kinetic energy and potential energy conversion formula of junior high school physics is enough to answer the relationship between the closing speed and the height of the water column. That is: 0.5MV^2 =MgH, substituting the ending speed, we can get: when the ending speed of the raindrop is 8 meters/second, H=3.2 meters; when the ending speed of the raindrop is 9 meters/second, H=4.05 meters; the ending speed of the raindrop When it is 2 meters/second, H=0.2 meters.
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