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Why barbed needle?
Physics | Why barbed needle?
It would seem that this question is so simple and the answer is so obvious that it should not have and consider. Nevertheless go in some detail in the subject. It is known that even a piece of cardboard with a blunt nail puncture sometimes does not work. Although the applied force is the same. What is the secret of a sharp object such as a nail or a conventional sewing needle? Christmas tree needle pricked for the same reason, which will be revealed below. High technology confidently dominate , attracting everyone’s attention. Meanwhile remain invisible interesting facts. Physical facts, which is based on the use of our entire civilization.
All business in the area. In blunt nail area “island” and more, respectively, the force is distributed over a larger surface. And the sharp tip area is minimal, and any attachments thereto, efforts are focused on her slimline tip.
Farmers know that the less harrow teeth, the deeper it vspashet soil. The reason for this behavior agricultural tools is that the fewer teeth, the large load is applied to each tine.
One force is insufficient. Plays a huge role as an area to which the force is applied. Suffice it to cite a simple example. If you know that the employee receives 100 thousand rubles, it is impossible to say how much this lot. After all, it could be as annual and monthly wages on. Since force is the case in the same way, one and the same force can be applied to an area of a square inch, or one hundredth to one square millimeter.
The most famous example: skiing. They are able to keep people on the loose snow, which he will fail if shod in the most ordinary shoes. It is clear that the whole thing in the area that have skis significantly greater than that of even the largest shoe size. This means that the weight of the human body is distributed to the entire area of the ski, instead of the relatively small area of the soles shoelace. Assume that the ski area twenty times exceeds the area of winter footwear soles. This means that the skier has on the surface of loose snow twenty times less pressure than those who paces the white cover boots. The weight of both can be equal. Snow skier stand, and no pedestrian.
For the same reason the horse has to work in a swampy area, “shoes” in a special way. To her hooves special tie (like the people they are called) “shoes” that make the area more support. This means that the pressure is reduced to the swamp and horses legs do not sink into the swamp. I must say that such “swamp” and used by people. On the ice is not strong enough person moves on all fours. Thus the weight is distributed over a larger area. These are examples of situations where it is necessary to increase the area of support. But in the case of a nail with a needle so it must, on the contrary, decreased.
Crawler tractor, and especially tank, weigh a lot. But in loose soil they get stuck. The whole thing just in weight distribution of these massive machines on a large area of the tracks. Vosmitonnaya whopper weighs per square centimeter of soil just six hundred grams. Special tracked freight cars for the swamps carries two tons of luggage, and the pressure is only 160 grams per square centimeter. This allows him to “stay afloat” in peat bogs, sand-covered spaces and swamps.
From the foregoing it is clear that only the tip pierces through insignificance area on which the action is distributed forces. Completely for the same reason a sharp knife cuts better than a dull: the power is concentrated in a smaller space.
It is now clear that the tip of the nail or sewing needle so easily pierces the material because the tip area of these items is extremely low. For this reason, a sharp knife is easier to cut than blunt. After accompanying cook whole force is concentrated on a small area of a sharp blade. Area blunt blade some more. In other words, sharp objects pierce and cut so well because of their sharp endings concentrated all the force applied to an object.
Mankind has learned to use these physical properties. Therefore, when necessary, the pressure force is concentrated in a minimum of one “point”. And when you need it to disperse the largest possible surface. This is a fact and not a myth or assumption. And only thanks to him that people have long learned to sew clothes. So even the most stylish jeans carry particle discussed above ideas. This brief overview allows briefly return to the past – in the days when mankind gladly opened up new physical laws. And the theory was interesting practice.
On the grounds of “Entertaining Physics” Ya.I.Perelmana
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