Naked Science Forum
General Science => General Science => Topic started by: jfoldbar on 03/07/2022 18:26:43
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i was on a construction site. i had a rope/pulley on a 6 story building and i was pulling up scaffold pieces. a few of us was at this for about a week. we noticed that the rope/hook end always spins. so the scaffold piece was spinning as it was going up.
any idea what causes this? is it the Coriolis effect, or just human "error". since the scaffold piece was twisting, why doesnt the rope twist up?
the rope was new. it made no difference who pulled the rope. rope length is 6 stories up, then 6 stories back down. so total about 36 meters. from the underneath side looking up, the scaffold spun clockwise.
after being at this for days and pulling up more than 1000 scaffold pieces, the rope was showing no signs if twist in it.
hope this makes sense. we were curious as to why it spun.
TIA.
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Most ropes have a twist to them; sometimes it's obvious, sometimes not.
But when you hang a load on the rope, it untwists a bit, and that's why the scaff poles twist.
But when you let the load off, it untwists again and that happens when you lower the rope back. But you are less likely to notice that.
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from the underneath side looking up, the scaffold spun clockwise.
That would make sense. Most ropes of this sort are 3 strand with a right hand lay. This means that in construction the rope is tightened by twisting the end anticlockwise, so when it is stretched (as described by @Bored chemist ) it will untwist clockwise when viewed from below.
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How was the rope attached to the scaffold? Did it always spin the same way? When you shorten a rope any misallignment in the attachment will be exacerbated.
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Pulleys are a type of work transmission device (Force x Distance). Pulley systems effectively reduce the amount of force required to pull an object while increasing the distance required to pull.
Using a simple 2:1 pulley system, moving a 10kg distance of 1m would require pulling 2m of rope with a force of 5kg.
The pulley advantage can then be increased to lift very large loads slowly.