It's not unusual to encounter rain in the wild. For wild sports enthusiasts, an impact garment with good waterproof function is a must-have. The waterproof function of impact clothing is closely related to its waterproof index.
Let us first understand this index briefly. Their unit is millimeter water column pressure. The usual explanation is that when a 10000mm high water column is pressed on the fabric, the water seeping from the fabric does not exceed 3 drops in 24 hours, then we think The waterproof index of this dress is 10000mm.
So there is the following question, what is the difference between 3000mm, 6000mm waterproof pressure and 10000mm waterproof pressure? What kind of target impact clothing should I buy? Obviously, the higher the waterproof index, the stronger the waterproof function, and of course the higher the price. The key to choosing the impact suit under the target depends on your own practical needs, and the right one is the best. If it is only used for city tours and daily outdoor wear, the waterproof index is 3000mm to 5000mm; if it is a quasi-professional hiking, camping or crossing activities, the impact underwear with a waterproof target of 6000mm to 8000mm is enough to deal with it comfortably; but If you need to go to the environment with more difficult natural conditions for professional mountain climbing, adventure and other field activities, it is best to choose impact underwear with a waterproof index of more than 10000mm.
We often hear that the rainproof of this impact suit reaches 6000, and the rainproof index of that impact suit is 10,000. 6000 and 10000 here are measured in millimeters of water column pressure. The usual explanation is that when a 10000mm high water column is pressed on the fabric, the water seeping from the fabric does not exceed 3 drops within 24 hours, then we think that the waterproof index of this garment is 10000mm. So someone asked, what is the difference between 6000mm waterproof pressure and 10000mm waterproof pressure? What kind of target impact clothing should I buy? And so on similar questions. So good, let's start from the beginning.
The ending speed of raindrops
If there is no air (resistance), the clouds on the day will turn into rain and then fall. After accelerating the movement all the way, the speed when reaching the ground will reach 300 meters per second, which is basically equivalent to half the speed of a bullet. There will be no living creatures on land. Thank God, because of the existence of air resistance, when raindrops form and begin to fall, they will move faster (acceleration gradually decreases) after a short time. When the air resistance of raindrops is equal to its own gravity, ok, at this time, raindrops begin Enter the stage of constant falling until it reaches the ground. In physics, this uniform speed is called the ending speed of the object.
The size of the raindrops
It has been concluded that in general, 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 found that if the water particles are smaller than 0.5mm, then due to the effect of the updraft in the atmosphere, it is enough to keep water particles of this size in the air. The size of raindrops generally does not exceed 6mm. Due to the existence of air resistance, large raindrops tend to decompose into many tiny raindrops with a sharp decrease in volume during the falling process. In addition, these large raindrops keep bumping against each other as they fall, which also promotes their collapse. Scientists have found that under laboratory conditions, large raindrops usually begin to break apart when they reach about 5 millimeters in diameter. In the clouds, when the large raindrops reach 5 mm in diameter, they are usually shattered due to collisions. This is why raindrops with a diameter of 5 mm or even larger are rarely seen on the ground, because raindrops cannot avoid the fate of colliding with many other similar species.
Raindrop size and finishing speed
The ending speed of raindrops has a strong correlation with the size of raindrops. Generally speaking, the ending speed of drizzle (0.5mm in diameter) is 2 m/s, and the maximum ending speed of raindrops in heavy rain (the maximum diameter of raindrops is about 5.5mm) is 8-9 m/s.
Finishing speed and water column height
With the finishing speed, the final kinetic energy of raindrops can be known. The conversion formula of kinetic energy and potential energy in junior high school physics is enough to solve the relationship between the finishing speed and the height of the water column. That is: 0.5MV^2 = MgH, substituting the tailing speed, we can get: when the tailing speed of raindrops is 8m/s, H=3.2m; when the tailing speed of raindrops is 9m/s, H=4.05m; raindrops are ending When the speed is 2m/s, H=0.2m;
Incorporating some factors (infiltration, increasing thickness to extend the service life of the waterproof membrane, etc.), if it is only used for city tours and daily outdoor wear, the 6000mm waterproof target impact underwear is sufficient to deal with it. But if you need to go to a more difficult environment, it is best to choose impact underwear with a waterproof index of more than 10000mm.