L’aspirisouffle Flight of fancy
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- LIBRE PARCOURS MOYEN
29 J’ai compris ! _____________________________________________________________________ I see…
_____________________________________________________________________ Разбрах! _____________________________________________________________________ Pour voler, apparemment, il doit suffir de souffler de l’air vers le bas. _____________________________________________________________________ To fly, apparently, all you have to do is blow air downwards… _____________________________________________________________________ За да полетя, очевидно трябва да падна. _____________________________________________________________________ Essayons ceci _____________________________________________________________________ Let’s give it a try. _____________________________________________________________________ Да опитам така.
_____________________________________________________________________ Hmmm…not very effective! _____________________________________________________________________ Хм… Нещо не се получава… _____________________________________________________________________ PSCHOUF ………………………………. ПШТ ………………………………………………………… Regarde, Anselme, les ailes des oiseaux n’ont pas la forme de parapluies ! Tu veux toujours tout comprendre tout de suite. Il faut continuer… _____________________________________________________________________ Look, Archie – birds aren’t shaped like umbrellas! Don’t worry; you’ll understand it all pretty soon. Just carry on… _____________________________________________________________________
_____________________________________________________________________ You’re so right, Sophie! _____________________________________________________________________ Права си, Софи! _____________________________________________________________________ Elle n’est pas mal roulée ! _____________________________________________________________________ Доста добре е сложена! _____________________________________________________________________ Vous n’êtes pas mal enroulée non plus _____________________________________________________________________ Вие също сте добре навит. _____________________________________________________________________ mmm… _____________________________________________________________________ Mmmmm… _____________________________________________________________________ Хм… _____________________________________________________________________ 30 ECOULEMENTS A DENSITE CONSTANTE _____________________________________________________________________ INCOMPRESSIBLE FLOW _____________________________________________________________________ ТЕЧЕНИЯ С ПОСТОЯННА ПЛЪТНОСТ _____________________________________________________________________ L’expression “libre comme l’air” n’est pas un vain mot. Les molécules d’un gaz ont horreur de la promiscuité. Elles ont à cœur de maintenir le plus de distance possible entre elles. _____________________________________________________________________ The expression “free as the air” isn’t just a hollow phrase… Gas molecules hate crowds. They try to stay as far apart as possible. _____________________________________________________________________
_____________________________________________________________________ I’ll never make the air denser this way! _____________________________________________________________________ Не мога да увелича плътността на въздуха с такива средства. _____________________________________________________________________ Raté ! Tu n’es pas assez rapide ! On t’a vu venir _____________________________________________________________________ Yah, missed! You’re too slow! I saw you coming! _____________________________________________________________________ Напразно! Не си особено бърз. Видях те като идваш. _____________________________________________________________________ Qu’est-ce qui fait fuir les molécules au moment où les raquettes se rapprochent ? _____________________________________________________________________ Why do the molecules get out of the way as soon as the paddles come together? _____________________________________________________________________ Какво кара молекулите да се разбягват в момента, в който двете ракети се доближават? _____________________________________________________________________ La trouille peut-être ? _____________________________________________________________________ They get scared? _____________________________________________________________________ Може би ги е страх? _____________________________________________________________________ 31 Il faut imaginer une place sur laquelle errent des gens qui ont les yeux bandés. Ils vont jouer le rôle des molécules et la vitesse à laquelle ils se déplacent, au hasard, en tout sens, sera une image de la vitesse d’agitation thermique V. _____________________________________________________________________ To see what the molecules are doing, imagine a place where every body wanders around with blindfolds on. The people will play the role of molecules – and the speed they move at, haphazardly (more hazard than hap!) is the analog of the thermal agitation V. _____________________________________________________________________
_____________________________________________________________________ They go nowhere in particular. Every t second, on average, after traveling a distance l, they collide. We call l the MEAN FREE PATH and t the MEAN FREE TRAVEL TIME. _____________________________________________________________________ Те нямат конкретна посока. Всички t секунди средно, след като изминат разстояние l, се сблъскват. С l се обозначава СРЕДНАТА ДЪЛЖИНА НА СВОБОДНО ДВИЖЕНИЕ, а t е СРЕДНОТО ВРЕМЕ НА СВОБОДНО ПРИДВИЖВАНЕ. _____________________________________________________________________ Dans l’air que nous respirons, V, vitesse d’agitation thermique, est proche de 340m/sec. Le libre parcours moyen moléculaire est voisin d’un cent millième de centimètre, tandis que le temps qui s’écoule entre deux collisions d’une molécule avec ses voisines n’est que d’un dix millième de seconde. _____________________________________________________________________
_____________________________________________________________________ Във въздуха, който дишаме, V – скоростта на топлинното движение, е близка до 340 м/сек. Средният свободен молекулярен пробег е близък до една сто хилядна част от сантиметъра, докато времето, което изминава между два сблъсъка на една молекула със съседните й, е равно на една десетхилядна от секундата. _____________________________________________________________________ Rien n’incite ces gens aux yeux bandés à s’assembler, au contraire : leur mouvement d’agitation incessant amènerait tout attroupement de diamètre D à se disperser en un temps D/V.
_____________________________________________________________________ There is nothing to make these blindfolded people collect together. On the contrary – their random movements tend to disperse any group of diameter D in a time D/V. _____________________________________________________________________
_____________________________________________________________________ C’est en effet le temps qu’il faut à ces personnages pour parcourir la distance D, donc pour quitter le lieu de l’attroupement. _____________________________________________________________________ Essentially this is the time one person takes to move distance D – thereby leaving the group. _____________________________________________________________________ Това е времето, необходимо на тези хора, за да изминат разстоянието D, тоест, да напуснат мястото, в което се натрупват. _____________________________________________________________________ 32 Ces gens, muets par surcroît, ne voient pas plus loin que le bout de leurs mains. Si un objet pénètre dans cette foule à une vitesse V inférieure à la vitesse d’agitation V, les personnages pourront s’en informer, en se heurtant, de proche en proche. Et ainsi ils pourront s’écarter AVANT que l’objet ne soit sur eux. Cette information chemine à la vitesse de leur marche, c’est-à-dire à la vitesse d’agitation V. _____________________________________________________________________ These people – who we assume are also struck speechless – can only “see” as far as their arms can reach. If something moves into the crowd at a speed V lower than their speed of movement V, then the people can tell each other about it, step by step, by bumping into each other. So they can get out of the way BEFORE the object hits them. This information moves at the same speed they do – that is, the velocity of agitation V. _____________________________________________________________________
_____________________________________________________________________ SOUND is the propagation, at constant density, of a pressure – impulse. It’s a sort of wave of jostling, and it moves with a speed equal to V. _____________________________________________________________________ ЗВУКЪТ представлява импулс на налягане с ПОСТОЯННА ПЛЪТНОСТ на средата. Това е нещо като вълна на сблъсък, която се разпространява със скорост V. _____________________________________________________________________ Il faut bien comprendre que le son est la propagation d’une impulsion et non une propagation de matière. _____________________________________________________________________ It’s important to realize that sound is a propagation of IMPULSES, and not a propagation of MATTER. _____________________________________________________________________ Трябва много добре да разберем, че звукът е разпространение на импулс, а не на материя. _____________________________________________________________________ Le son est une ONDE de PRESSION _____________________________________________________________________ Sound is a PRESSURE WAVE. _____________________________________________________________________ Звукът е ВЪЛНА НА НАЛЯГАНЕ. _____________________________________________________________________ C’est à la vitesse du SON que les molécules sont averties du moindre déplacement des raquettes d’Anselme. Elles peuvent donc s’enfuir aisément en maintenant leur DENSITE CONSTANTE. _____________________________________________________________________ The molecules fled from Archie’s paddles at the speed of sound. They could do this easily while maintaining CONSTANT DENSITY, because the bats were moving much more slowly than sound. _____________________________________________________________________ Именно със скоростта на ЗВУКА молекулите са известени и за най-малкото преместване на ракетите на Анселм. Следователно те могат лесно да избягат, запазвайки своята ПОСТОЯННА ПЛЪТНОСТ. _____________________________________________________________________ 33 Anselme a aligné des boules de croquet. Il communique une impulsion à la première qui la transmet à la seconde…et ainsi de suite : Image linéaire de la propagation du SON. _____________________________________________________________________ Archie lines up some croquet balls. He gives an impulse to the first one, which transmits it to the second, and third…and so on. This is a one-dimensional image of the propagation of sound. _____________________________________________________________________
СЪОТНОШЕНИЕТО M = V / V ЩЕ БЪДЕ НАРЕЧЕНО СПОРЕД ОПРЕДЕЛЕНИЕТО, ЧИСЛО НА МАХ. V Е СКОРОСТТА НА ЗВУКА. АКО V < V, ТОЕСТ, АКО M < 1, ФЛУИДЪТ ЩЕ СЕ ДВИЖИ СЪС СКОРОСТ, ПО-МАЛКА ОТ ТАЗИ НА ЗВУКА. ТЕЧЕНИЕТО ЩЕ СЕ ИЗВЪРШИ ПРИ ПОСТОЯННА ПЛЪТНОСТ, ТО ЩЕ БЪДЕ НАРЕЧЕНО „ НЕСВИВАЕМО”. Ръководството
_____________________________________________________________________ BERNOULLI’S LAW _____________________________________________________________________ ЗАКОН НА БЕРНУЛИ _____________________________________________________________________ Ça ne sent pas très bon, ici ! _____________________________________________________________________ It’s a bit smelly in here! Phew! _____________________________________________________________________ Тук не мирише особено приятно! _____________________________________________________________________ Ça sent la taupe ! Qu’est-ce que tu veux que ça sente ? _____________________________________________________________________ It smells of moles – what else do you expect? _____________________________________________________________________ Мирише на къртици. А ти на какво друго искаш да мирише? _____________________________________________________________________ Voyons, voyons, Daniel Bernoulli : physicien suisse, 1700-1782 _____________________________________________________________________ Let me see, let me see…Daniel Bernoulli, Swiss physicist, 1700-1782… _____________________________________________________________________ Я да видим. Даниел Бернули, швейцарски физик, 1700-1782. _____________________________________________________________________ Comme cela, ça devrait aller _____________________________________________________________________ That’s it. It ought to work. _____________________________________________________________________ Ето така ще оправим работата. _____________________________________________________________________ Qu’est ce qu’il fricote là-haut ? _____________________________________________________________________ What’s he playing at up there? _____________________________________________________________________ Той какво човърка там горе? _____________________________________________________________________ 35 Voilà, ça y est. _____________________________________________________________________ There, that’s it. _____________________________________________________________________
_____________________________________________________________________ Ça y est quoi ?! _____________________________________________________________________ That’s what? _____________________________________________________________________ Какво е готово? _____________________________________________________________________ Mon système de ventilation automatique _____________________________________________________________________ My automatic ventilation system _____________________________________________________________________ Моята автоматична система за вентилация. _____________________________________________________________________ Le vent souffle, c’est bon ! Tu sens l’aspiration ? _____________________________________________________________________ The wind’s blowing. Great! You can fell the suction. _____________________________________________________________________ Вятърът духа, прекрасно! Усещаш ли течението? _____________________________________________________________________ Oui mais pourquoi est-ce que l’air du terrier est aspiré ? _____________________________________________________________________ Yes, but why does the air get sucked out of the burrow? _____________________________________________________________________ Да, но защо се всмуква въздухът от подземието? _____________________________________________________________________ Le tumulus est un obstacle au passage de l’air. Pour le franchir, celui-ce doit accélérer _____________________________________________________________________ The mound gets in the way of the air. To get past it, the air has to speed up. _____________________________________________________________________ Хълмът е препятствие за движението на въздуха. За да се преодолее това препятствие, движението му трябва да се ускори. _____________________________________________________________________ Accélérer, pourquoi ? _____________________________________________________________________ Speed up? Why? _____________________________________________________________________ Защо да се ускори? _____________________________________________________________________ 36 Comme dans les rapides d’une rivière _____________________________________________________________________ …like rapids on a river, when it narrows. _____________________________________________________________________
_____________________________________________________________________ Pour assurer un débit constant _____________________________________________________________________ to stop the flow from piling up … _____________________________________________________________________ За да се осигури постоянен разход. _____________________________________________________________________ Pigé ! _____________________________________________________________________ Gotcha! _____________________________________________________________________ Разбрано! _____________________________________________________________________ Bon, ça va plus vite. Mais je ne comprends pas pourquoi ça aspire ! _____________________________________________________________________ O.K, so it goes faster. But I still don’t see how the suction arises. _____________________________________________________________________ Добре, ето тук се движи по-бързо, но не разбирам как се осъществява всмукването. _____________________________________________________________________ Prends un élément de fluide (un paquet de molécules) qui passe par un rétrécissement. Son énergie va rester constante. L’accélération va donc se faire au détriment de l’énergie thermique, donc du mouvement d’agitation. _____________________________________________________________________
Look at a small element of fluid – a package of molecules – passing through a constriction like this. Its energy stays constant. The acceleration has to be compensated by a drop in thermal energy – less agitation! _____________________________________________________________________
_____________________________________________________________________ And that means the pressure drops. _____________________________________________________________________ И ако скоростта на безразборно движение намалее, ще намалее и налягането. _____________________________________________________________________ Comme la pression varie proportionnellement à la température et à la densité, cette pression va baisser. _____________________________________________________________________ Yes, because it’s proportional to the temperature, which is the thermal agitation. _____________________________________________________________________ И тъй като налягането се променя пропорционално на температурата и плътността, то също ще намалее. _____________________________________________________________________ Et c’est pour cela que l’air du terrier va être aspiré _____________________________________________________________________ And that’s what sucks the air out of this hole. _____________________________________________________________________ Именно заради това въздухът от подземието ще бъде всмукан. _____________________________________________________________________ 37 Mais, comment faites-vous pour être si savant ? _____________________________________________________________________
_____________________________________________________________________ Кога сте успели да научите толкова неща? _____________________________________________________________________ Dans le temps j’ai fait taupe _____________________________________________________________________ Oh, I’ve burrowed into a lot of things! _____________________________________________________________________ Докато си правех къртичината. _____________________________________________________________________ C’est curieux, à l’arrêt, la capote était toue détendue et pendait vers l’intérieur. Et maintenant que nous roulons, elle est toute gonflée vers l’extérieur. _____________________________________________________________________ It’s funny – when we stop the roof is all slack and hangs down inside; but now that we’re moving it’s swollen outwards! _____________________________________________________________________ Любопитно е, че когато спряхме, гюрукът на автомобила бе отметнат и висеше навътре. Сега обаче, когато се движим, той се наклони на външната страна. _____________________________________________________________________ Pourtant l’air frappe dessus ! _____________________________________________________________________ And yet the air is pushing against it. _____________________________________________________________________ А въздухът натиска отгоре. _____________________________________________________________________ C’est la même chose que pour le terrier de la taupe. La 2CV lui ressemble un peu non ? _____________________________________________________________________ It’s just like the molehill. You know, this car looks quite like one, doesn’t it? _____________________________________________________________________ Същото се отнася и за дупката на къртичината. Нашият автомобил малко прилича на него, нали? _____________________________________________________________________ Alors l’air doit accélérer pour contourner la voiture à densité constante. La température baisse, donc la pression aussi et la capote est aspirée. Pigé. _____________________________________________________________________ Oh – so the air has to accelerate to get past the car at constant density. Then the temperature drops, the pressure does too – and the roof swells. I see now. _____________________________________________________________________
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