# How would putting a blanket over a rope or chain under tension (i.e. pulling a truck out of sand/mud) work to reduce the risk of it flying out and hurting someone should it snap?

71 views
0

Awhile back I helped pull a couple of guys who’d gotten their truck stuck in the sand out using a couple of heavy cargo straps that I had in my truck.

One of the guys put a blanket over the straps and said it would dissipate the energy should the straps snap. It sounded plausible to me, but curious if it’s a legit claim.

In: 72

When a cord snaps, the newly free end moves *very* quickly, as all the force the cord was under is transferred into motion at that one free end. This is what makes it dangerous, because even though the cord is very light, with that much speed it can still hurt you.

With a blanket on top, if the cord snaps, the free end will collide with that big piece of fabric when it tries to move, and all that force will be distributed to that fabric, which will probably just ripple. It’s the same amount of force, but it doesn’t generate the same speed now as it’s acting on the whole blanket rather than the very end of the cord.

[Here](https://www.reddit.com/r/dataisbeautiful/comments/uo0ooa/oc_velocities_of_different_parts_of_a_whip/) is a nice simulation of what’s going on at the end of a whip. You can see that if anything was impeding it’s movement, it wouldn’t gain nearly so much force at the tip.

[removed]

Tension works in weird ways. Cloth can be really good at spreading any built up tension as the energy needed to move the cloth any considerable distance ends up being quite high.

There’s a pretty cool experiment you can do to show the power of how a light item will disperse energy. Find a wooden or plastic ruler and lean it over the edge of a table. On top of the ruler on the table, place a piece of paper. Then try to catapult that piece of paper by swiping down on the ruler over the edge of the table.

That piece of paper is so good at dispersing the energy of your hand on the ruler that it’ll actually snap the ruler in half. That’s, effectively, how the blanket would work on the strap.

they’re called recovery dampers, if you wanna google them.

basically, when a cable breaks, all of the energy stored in it can only leave through whatever the cable strikes. it’s not actually a lot of energy, but it tends to be heavily concentrated at whatever it hits. the damper forces a lot of that energy to be spent differently, preventing it from being concentrated into a single whipping strike.

The blanket helps in 2 ways. The first way is the blanket spreads out the impact of the small thing moving at high speed. It can be demonstrated with a rubber band. This assumes the blanket is heaver than the rope.

snap a rubber band on your bare skin = ow

snap a rubber band on a hoodie you are wearing = barely feel it

now if a chain snaps a blanket won’t help as much with spreading the impact because chains are heavier than blankets, however the blanket will still help because it will provide wind resistance to slow down the chain so essentially the air is now absorbing the impact through friction.