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Why does paper fold so well?

bbc.co.uk

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Re: Why does paper fold so well?

#51

Post by oidar »

srean wrote: post #6

Oh no! woe is me, they don't highlight my absolutely, ridiculously favourite fact/curiosity about a sheet of smooth paper: If you fold it clean, the crease is a straight line. In fact I don't know of any other good way of obtaining a straight edge from scratch quickly, meaning without transporting one existing straight edge to another (*). I remember spending a lot of enamored time coming up with different geometrica…

> If you fold it clean, the crease is a straight line. In fact I don't know of any other good way of obtaining a straight edge from scratch quickly, meaning without transporting one existing straight edge to another.

It would be interesting to see how progressively larger pieces of paper handle this. A roll of masking paper would be the easiest way to test.

Re: Why does paper fold so well?

#52

Post by rolph »

dotancohen wrote: post #30
globular-toast wrote: post #20

Earlier quoted context omitted.

> In fact I don't know of any other good way of obtaining a straight edge from scratch quickly A string made taut between two points is surely a better way? And works at much bigger sizes too (people build walls and foundations using this technique all the time). The paper is less useful in practice because any paper you find is probably straight and square anyway. Still, I had fun thinking about this as I definitely…

Over long distances the string will sag in the middle. That's one of the reasons (not the only reason) construction uses lasers today.

yeah its pretty hard to get new help to pull hard without fear of breaking the tool, coincidentally the beam width of a laser will increase over long distance, similar to line slack sagging over long distance.

Re: Why does paper fold so well?

#53

Post by dotancohen »

rolph wrote: post #52
dotancohen wrote: post #30

Earlier quoted context omitted.

Over long distances the string will sag in the middle. That's one of the reasons (not the only reason) construction uses lasers today.

yeah its pretty hard to get new help to pull hard without fear of breaking the tool, coincidentally the beam width of a laser will increase over long distance, similar to line slack sagging over long distance.

The DeWalt that I've been using recently had a bright green line pencil thin, in the sun, easily ten meters from the device. That's far enough to do an entire patio - ten meters in each direction. I don't know about longer needs, such as sidewalks, but for building construction the DeWalt was excellent.

I've never tried other brands.

Re: Why does paper fold so well?

#54

Post by IAmBroom »

UltraSane wrote: post #37
bena wrote: post #28

Earlier quoted context omitted.

This is actually a tool used in construction. A chamber filled with chalk and a coiled line. You hook the line to one end of your item, pull the chamber across, make it tight, snap the line. https://www.homedepot.com/p/Milwaukee-100-ft-Bold-Line-Chalk...

Using one of these to snap a perfect reference line is extremely satisfying.

"Perfect" is doing some heavy lifting here. The string is always a non-straight catenary curve, unless infinite force is used to pull an indestructable string.

A laser beam* across the room will show the defect in the string straightness. It's more than good enough to fool human eyes, which are not good at judging slow gradients (such as all the touristy "mystical anti-gravity locations" where balls roll apparently uphill). Therefore, the snap-line is good enough. But not perfect.

* Gravity of course still affects the laser beam's straightness, but on a level good enough to fool electron microscopes, so we can give that a pass.

Re: Why does paper fold so well?

#55

Post by IAmBroom »

Peterz_shu wrote: post #24

It has a lot of air gaps within its fibers. We know that Solids CANNOT be compressed. So what's actually being folded is the air gaps. Which is why you can't easily fold a piece of tungsten. It has less air gaps.

Pretty sure the material's innate stiffness plays a role there, too.

Metallic film folds quite nicely.

Re: Why does paper fold so well?

#57

Post by rolph »

dotancohen wrote: post #53
rolph wrote: post #52

Earlier quoted context omitted.

yeah its pretty hard to get new help to pull hard without fear of breaking the tool, coincidentally the beam width of a laser will increase over long distance, similar to line slack sagging over long distance.

The DeWalt that I've been using recently had a bright green line pencil thin, in the sun, easily ten meters from the device. That's far enough to do an entire patio - ten meters in each direction. I don't know about longer needs, such as sidewalks, but for building construction the DeWalt was excellent. I've never tried other brands.

the really serious guys use GPS based equipment, and its serious stuff, being able to center up on a 1/64 inch brad tacked into the asphalt.

[that 50,000$ ufo on a tripod by the highway, dont try to steal one, man do they ever know exactly where they are]

yeah i like team yellow too :) the beam spread is what you want to check out if your serious about > 100 ft distance

https://www.gpsalaska.com/

^ this is a very commercial website, but example of higher end equipment and technique

Re: Why does paper fold so well?

#58

Post by UltraSane »

IAmBroom wrote: post #54
UltraSane wrote: post #37

Earlier quoted context omitted.

Using one of these to snap a perfect reference line is extremely satisfying.

"Perfect" is doing some heavy lifting here. The string is always a non-straight catenary curve, unless infinite force is used to pull an indestructable string. A laser beam* across the room will show the defect in the string straightness. It's more than good enough to fool human eyes, which are not good at judging slow gradients (such as all the touristy "mystical anti-gravity locations" where balls roll apparently u…

You can usually put enough tension on the string to make any droop negligible. But yes modern laser levels are a better if less tactile option in some cases.

Re: Why does paper fold so well?

#60

Post by Cthulhu_ »

bena wrote: post #28
wongarsu wrote: post #27

Earlier quoted context omitted.

If you want to use a rope to get a straight line, your best bet is to turn the rope itself into the pencil. Coat it in chalk or other powder, then put it under tension and snap it on to the desired surface

This is actually a tool used in construction. A chamber filled with chalk and a coiled line. You hook the line to one end of your item, pull the chamber across, make it tight, snap the line. https://www.homedepot.com/p/Milwaukee-100-ft-Bold-Line-Chalk...

It's technology that goes back thousands of years, here's one from the Iliad: https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext....

I love youtube manufacturing videos, saw one where they made a wooden Japanese one that has like a hopper of soot where the string is pulled through.

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