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Channel: GetAClass - Physics in experiments

физика

physics

science

наука

статика

сопротивление материалов

строительная механика

механика

опыты по физике

эксперимент в школьной физике

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[music] the

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bridge company next to which I am now

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is a monument to the railway bridge

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across the Ob,

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built more than 100 years ago on the

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Trans-Siberian Railway, and it is from

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this bridge that the history of the city of Novosibirsk begins,

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then we see the current railway

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bridge across the court which stands on the same

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supports and ours today's video

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will be devoted to the designs of bridge companies

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and how the load is distributed in the

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elements of these structures,

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and in order to understand what

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advantages such a structure as a

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truss provides, we will recall the problem that in 2013 the

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participants in the international

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tournament of young physicists solved, the

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problem was called do it yourself and it

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suggested from an ordinary sheet of

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A4 paper using a small

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amount of glue, build a bridge

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that would span the span of the length of

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this sheet by a little less than 30

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centimeters and would withstand the maximum

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load, and then we began our experiments by

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gluing tubes from a

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4 sheet and testing to test their strength in

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this way, a

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load will now be applied in the middle, I pull the

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force sensor and see at what force the

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tube will break;

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to

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bend and it is clear that it is not at all

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difficult for me to do this with my hands; it will break in the

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center where the bending moment will be the

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largest, but if we stretched it, it

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would withstand much more

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force, and even if we compressed

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along its axis the forces that are required

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in order to it has lost stability

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in this position, they are also quite large,

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probably if I press with my whole palm, I

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can and break it with one finger, I ca

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n’t do this, well, what

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if we built a structure in

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which all the elements worked in

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tension, or if we pressed it and there would be no

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working elements in bending,

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such a structure would probably be

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very strong and trusses, at least in

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their simplest version, are precisely

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this kind of

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structure; the

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simplest firms are assembled from

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triangles because a triangle

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is a rigid geometric figure,

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and here we have assembled such a firm; we

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will apply a load to its central node, the

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vector sum of the forces acting in any

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node of the firm must be equal to zero,

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so 2 inclined braces coming from the

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central node work in tension,

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let's now see what happens to the two

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upper nodes of the trusses and we pull the

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central braces and the tensile forces

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must be balanced by the compressive

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forces in the central beam and in On the lateral

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braids, we just need to figure out the

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balance of forces in the nodes at the edges of the bridge;

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we will depict the compressive forces in the lateral

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braids and the support reactions so that the side nodes

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remain in balance; we need to add

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tensile forces to the external beams;

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we will depict the same tensile forces in the

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central node;

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thus, we have obtained the distribution

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forces and we see which elements of the truss

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work in compression

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and which in tension,

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but now the time has come for tests for

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different companies and the first will be this

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design, it is made of a

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horizontal beam of a vertical rod and

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2k shortened ok when we load the

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beam the rod will transfer the load to the braces

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they will stretch they'll take the weight on themselves and

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start chewing the rod from the ends, and

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we'll see, most likely, of course, the braces

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will break, and maybe the rod

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will lose stability, well, let's

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test it, put a sensor on the ribbons, now

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we need to connect the sensor, well, we started

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pulling 5 newtons in 10 15 20 something

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went I have but 25 30 35 already 40

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newtons, marik is still holding on, he

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bent 45 and a breakdown occurred,

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now we will test the second bridge

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structure, it’s arranged like this, that means 4

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downward braces, so they

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are held in place by these tapes,

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when I start loading everything will come apart,

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you can help, that means the load will be

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applied from above, again the load is

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transferred to the braces,

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they stretch the lower tapes, and again I

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turn on the recording and apply efforts of 10

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newtons 2025 so you need to correct it a

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little so that it does not move 25 30 30

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40 at 40 newtons you are broken and we

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remember that

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the tube made from sheet 4 could withstand only 20

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Newtons, it was a good test,

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so this kind of bridges are made from

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trusses from us, by the way, where the

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loss of stability occurred, this

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leg broke, which means that this kind of bridges can

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withstand, in any case, about

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twice the load, a similar

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design has the most the youngest of the

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Novosibirsk bridges, the Burinsky Bridge,

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its load-bearing truss consists of two

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arches inclined to each other, and already on

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these arches the road surface hangs on cables.

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When in 2013, the task of inventing it yourself

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about bridges from a sheet of A4 paper

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was played at a tournament of young physicists, there

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were such bridges on the floor It’s

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a lot, but we still weren’t able to get a structure

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that would confidently withstand a load

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of 50 newtons created by a load of 5

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kilograms,

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maybe you can come up with something like that,

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and as for our bridge, I’d

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like to test it on a more full-scale basis,

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and here I have it three and a

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half kilograms of lead and other

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iron, and now I’m going to risk this load, well

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hang our vintage bridge carefully, we

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see how the lower bands are stretched, I

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let go and the load hangs, the bridge withstood it,

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and now we are in a place

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where we can see as many as four Novosibirsk

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bridges closest to we have a metro

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bridge, this is a box closed on all

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sides and the train goes inside this box, the

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next automobile communal

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bridge, then you can see the railway bridge near

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which our shooting today began,

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and even further away you can see another

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automobile bridge and you see that the

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designs of all these four tails are

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different but and at this point I would like to

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ask what is the advantage of

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this or that design, why engineers do

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not build all bridges the same but

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each time they choose some other

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device, what is the reason for this, it is clear

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that this question probably has a short

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definite answer, and yet

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your thoughts on you can write this score

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in the comments to this video on

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youtube

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[music]

Description:

Ферма - это лёгкая и прочная конструкция, все элементы которой работают на сжатие либо на растяжение, и не работают на изгиб. В ролике мы делаем несколько мостов из листа бумаги А4 и испытываем их на прочность. Ключевые слова: статически определимая система, работа на растяжение, работа на сжатие, строительная механика, сопротивление материалов. Наш канал с дополнительными материалами https://t.me/getaclass_channel Новосибирский Государственный Университет https://www.nsu.ru/n/ Физический факультет НГУ

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