[Archive!] Pure mathematics, physics, chemistry, etc.: brain-training problems not related to trade in any way - page 48
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Самолёт взлетит, никуда не денется.
Why would it take off?
Why should it take off?
Why shouldn't it take off? It will take off for the same reasons it would under normal conditions.
Сергей, уж извини, но это слишком. Трудно даже представить, что ты заканчивал МАИ. Все-таки солидная контора.
От слов "механика системы меняется" хочется плакать. Можно подумать, что самолет знает источник силы, которая толкает его вперед: трос, винт, реактивный двигатель или твои собственные руки. Мало того, что знает, так еще имеет свободу вибирать свое поведение в зависимости от этого. Типа "от троса буду, а от винта - нет". А где тут физика, Сергей ? И куда ты засунул физические законы ?
Забудь на 5 минут свое МАИ, вспомни 8 класс школы. Элементарная задача на динамику Ньютона. Нарисуй самолет и все силы, которые при взлете к нему приложены. Дальше сам.
Больше на эту тему с тобой не дискутирую. Опасаюсь за свою психику.
PS
Это говорит только о том, как мало людей умеет пользоваться теми крупицами знаний, которые преподы с таким трудом и угрозой своей жизни, вколачивают им в головы. :-(
Хотя то, что темных больше - это аксиома.
You have a winch bolted to the ground and a rope pulling the aircraft off the transporter. And you think it's absolutely equivalent if the aircraft is being pushed by a propeller or a turbine attached to that aircraft?
That's really too much. I totally agree with you there.
This only shows how few people know how to use the little bits of knowledge that teachers thrust into their heads with such great difficulty and risk to their lives. :-(
-
There is a big difference between teachers and professors: teachers teach and lecturers grind it into their heads :)
If a ton of flies fly continuously in a closed volume, we can approximate replacing it with one equivalent fly. It would hang almost motionless in the centre of the volume and weigh one tonne. The difference in pressure above and below it will depend on the area of its projection on the floor, say for 1000 cm2 this difference is one atmosphere. But we need this difference to be maintained at all times, so our fly should simply hermetically divide the original volume into two equal volumes. If the initial pressure was P0, after our fly takes off it will be P1 under it and P2 above it. Neglecting thermal effects we will have P0 = (P1+P2)/2. The force acting on the fly will be (P1-P2)*S = 1t, the addition in the downward force will be (P1-P0)*S. Note that the areas are the same. Then given the condition P0 = (P1+P2)/2 we obtain for the lifting force the expression 2*(P1-P0)*S = 1t. By comparing it to the formula for the downward force (i.e. the weight) we see that the lifting force will be 0.5t.
A good solution. Just not completed to the end.
I quote: "the increment in downward force will be equal to (P1-P0)*S". Here (P1-P0)*S is the force acting on the floor of the volume where this fly is located. Isn't it true, Nikolai? Such formula is derived from the assumption that the pressure outside the plane = P0 (it was so until the fly flew in there). However, it is good to calculate what force acts on the ceiling of this volume. It is easy to see that it is equal to (P0-P2)*S. Substituting P0 = (P1+P2)/2 we will find out with surprise that the force also equals 0.5t. It is a mystery! And the sum of additions of forces acting on the floor and ceiling = 1t. That is exactly as much as the fly weighs.
It looks like someone has rigged it all up on purpose. :-)))
У тебя лебедка прикручена к земле и канатом стаскивает самолет с транспортера. И ты считаешь, что это абсолютно равноценно если самолет толкает винт или турбина, прикрепленная к этому самолету?
It makes absolutely no difference whether the jet engine pushes it or pulls the string.
The result is the same.
There is a big difference between teachers and tutors: teachers teach and pre-service teachers teach :)
Teachers teach those who want to learn. Those who don't want to learn are left free to choose. That is why a teacher (for me) is not a profession, but a vocation, a state of mind. A teacher is a profession. They pay money for it. Therefore the teacher should, is obliged to teach at least something even to those who in the grave saw all this knowledge. That's why you have to teach. Practice is meaningless and disgusting. But what can you do, that's how the modern education system works.
Хорошее решение. Только не доведено до конца.
Цитирую: "прибавка в силе, направленной вниз будет равна (P1-P0)*S". Здесь (P1-P0)*S - сила, действующая на пол объема, где находится эта муха. Не правда ли, Николай ? Такая формула получается из предположения, что давление снаружи самолета = Р0 (оно ведь было именно таким, пока туда не залетела муха). Однако, хорошо бы еще посчитать, какая сила действует на потолок этого объема. Нетрудно заметить, что она равна (P0-P2)*S. Подставляя Р0 = (Р1+Р2)/2 с удивлением обнаруживаем, что эта сила тоже = 0.5т. Мистика какая-то ! А сумма добавок сил, действующих на пол и потолок = 1т. То есть ровно столько, сколько весит мушка.
Похоже это все кто-то специально подстроил. :-)))
Yuri, I wanted to make everyone happy, but you've ruined everything :)
P.S. It would still be correct to say that the force acting on the floor will increase by half a tonne and the force acting on the ceiling from the inside will decrease by the same amount. The equal force will be directed downwards and will be 1t. And the external forces will not change in any way.
You have a winch bolted to the ground and a rope pulling the aircraft off the transporter.
Did I say that? I don't recall.
You have it bolted to the ground, the ground is standing on an elephant and the elephant is floating on a turtle. That's why you can't solve it, because you don't consider the speeds of the earth, the elephant and the turtle.
And you think it's absolutely equivalent if an aircraft is pushed by a propeller or a turbine attached to that aircraft?
Yuri, I was trying to make up and you ruined it.)
Shit, I'm sorry, I missed the point. :-)