The Fascinating Physics Behind Lift Cables | The Secret Genius of Modern Life- BBC

[Laughter] obviously I knew it was going to go so this string is made up of these multiple threads like this right now each one of these is of course capable of supporting a certain amount of weight a surprising amount of weight in fact which I can demonstrate over

Here let’s see how many of these 2 and 1/2 kilo bricks the threads hold when they’re separated out so 7 8 9 10 okay that’s 17 bricks total weight approximately 44 kilos thing is over time there’s kind of a high chance that one of these is going to break which I’m going to represent using the smallest pair of scissors that production could find right here okay you ready I’m actually quite nervous okay here we

[Laughter] go yeah I mean not ideal is it not ideal the problem is when you’re using individual threads as soon as one of them fails the load on the remaining ones is going to massively increase in a really dramatic way and cause them to fail which is exactly what happened there but

There is a trick that you can use to stop this from happening so I’m going to reset this and show you how it Works right let’s go again but this time when you look a string like this carefully you’ll notice that all those threads they’re twisted around one another like this exactly the same number of threads as before but that makes an incredible difference let me show You okay so now that is exactly the same number of bricks as before except this time because the threads are twisted it makes two key differences the weight of that lift is going to be spread throughout the threads much more evenly and secondly because of the friction that exists between these Twisted

Threads hang on what friction there’s friction because the threads have a rough texture which creates resistance making them grip Together anyway where were we because of the friction that exists between these Twisted threads it means that even if one piece fails it’s wrapped together so tightly that it will still support the structure of this string all the way down at least that’s the theory now

Makes sense why I’ve got such teeny tiny scissors okay here we go all right let’s see if I can get in there with one of these look at that there you go one thread’s gone and it’s holding look at that so at that point there now it’s

Only on two like nothing has changed we are using the same number of threads the same basket and yet one time it fails and the other time it doesn’t just because you twisted it together like it’s like hacking the laws of physics almost okay can I put more in the

Basket okay the first time it failed at about 44 kilos I’ve just added another 27 kilos nearly double I mean look I’m a mathematician so if I say it’s double you’ve got to go with [Laughter] it obviously I knew it was going to go my lizard brain made me jump I’m saying

Hanging on by a thread, literally… #SecretGenius #iplayer

Subscribe and 🔔 to the BBC 👉 https://bit.ly/BBCYouTubeSub
Watch the BBC first on iPlayer 👉 https://bbc.in/iPlayer-Home

Hannah Fry uncovers the secrets behind the miraculous technologies of the modern world, revealing the mind-blowing stories behind their invention.

All our TV channels and S4C are available to watch live through BBC iPlayer, although some programmes may not be available to stream online due to rights. If you would like to read more on what types of programmes are available to watch live, check the ‘Are all programmes that are broadcast available on BBC iPlayer?’ FAQ 👉 https://bbc.in/2m8ks6v.

11 comments

  2. That's exactly the problem, for computer science nobody works directly with integrals and matrices and it is your life work or maybe is a process adapted by newspapers to know who knows any math by the Enola Holmes looks or about to drop out the college. We can inspire the young ones to build bridges or some big severs someday with them knowing why this runs less than 10fps with more bricks. I really don't think rest of great Britain population does this with smallest scissors, but now I feel I'm not alone as a Zandalari troll with Jaina Proudmoore being that person I wish to become. Now I know it's biggest Jenga ever played by Julia Roberts or Sandra Bullock. But these relics of the past still here 0:30 and how heavy can be paper tubes? What this have to do with HTML and CSS, because this is how I'm about to change to Silicon Valley all the farm fields that need a hay transport. Should focus on some office, but I doubt it be some Technopolis.

  4. I wish that my old Physics teacher was as good looking as she and not the eccentric elderly man who had illegible handwriting on the blackboard but was very accurate at throwing pieces of chalk at inattentive pupils heads.

  9. I think the first experiment wasn't correct enough. You cannot tie 3 separate robes exactly the same length. So one robe will always be carrying mostly all load oneself.

  10. If the strings were rigged for equal load distribution, which they are not, there would be no difference in the magnitude of the failure load. The three lower rings (at 0:42) have friction against the larger ring to which they are clipped, such that when one string is cut the remaining two will not likely have equal loading, also, the way this is rigged does not prevent or allow for control over unequal loading due to variations in string elasticity. Twisting the strings into a rope results in a more equal load distribution than the unequally distributed rigging that was used. Construction rigging is normally designed to ensure equal load distribution to multiple cables when multiple cables are utilized. I think this video could be clearer on the causal factors involved.

Leave a Reply