Rainy days are not so annoying for outdoor enthusiasts. It is impossible for every trip to be a clear sky, which also loses a lot of fun. When traveling outdoors in rainy days, you should consider the waterproof performance of the equipment you choose. Here we will analyze it with you. Let’s take a look at the waterproof performance of the jacket
in the equipment.
The waterproof strength of the jacket is closely related to its waterproof index. Let us first briefly understand this index, their unit is the millimeter water column pressure, the usual explanation is that when A water column with a height of 10000mm is pressed on the fabric, and no more than 3 drops of water seeps out of the fabric within 24 hours, then we think that the waterproof index of this garment is 10000mm.
So there are the following problems, What is the difference between 3000mm, 6000mm waterproof pressure and 10000mm waterproof pressure? Which indicator 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 which index depends on your actual needs, and the most suitable one is the best.
If there is no air (resistance), the clouds on the day will turn into rain and fall down. After all the way of acceleration, the speed when they reach the ground will reach 300 m/s, which is basically equivalent to the speed of bullets. Half. There will be no living things on land at all. Thank God, due to the existence of air resistance, when raindrops form and start to fall, after a short period of variable acceleration (the acceleration gradually decreases), when the air resistance of the raindrops is equal to its own At this time, the raindrops begin to fall at a constant speed until they reach the ground. In physics, this constant speed is called the ending speed of the object.
In addition, some factors (wetting, Increase the thickness to prolong the service life of the waterproof membrane, etc.), if it is only used for inter-city travel and daily outdoor wear, the 6000mm waterproof jacket is enough to deal with it.
Some people have come to the conclusion that the general situation The diameter of raindrops is between 0.5mm and 6mm. In rare cases, the diameter of raindrops will reach 8mm or even 10mm (observed in the Hawaiian Islands).
Scientists have found that if the water particles are smaller than 0.5mm, then due to the effect of the updraft of the atmosphere, it is enough to keep water particles of this size in the air. The size of the raindrops generally does not exceed 6mm. Due to the existence of air resistance, large raindrops tend to fall in the process of falling. In addition, these large raindrops collide with each other as they fall, which also causes them to disintegrate. Scientists have found that under laboratory conditions, large raindrops usually reach a diameter of about 5 mm. It begins to disintegrate and disintegrate. In the clouds, when the large raindrops reach 5 mm in diameter, they usually break up due to collision with each other. 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 types.
The ending speed of raindrops has a strong correlation with the size of raindrops. Generally speaking, drizzle (diameter 0.5mm) The ending speed of the raindrop 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.
With the ending speed, you can know the last raindrop. Kinetic energy, the kinetic energy and potential energy conversion formula of junior high school physics, is enough to answer the relationship between the ending 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 m/s , H=3.2m; when the raindrop ending speed is 9m/s, H=4.05m; when the raindrop ending speed is 2m/s, H=0.2m;
so it is only used for inter-city travel , For daily outdoor wear, the waterproof index is 3000mm to 5000mm; if it is quasi-professional Outdoor hiking, camping or crossing and other activities, the waterproof index of 6000mm to 8000mm is enough for the jackets and pants; but if you need to go to the environment with harsh natural conditions for professional mountaineering, adventure and other outdoor activities, it is best to choose a jacket with a waterproof index of more than 10000mm Pants.
