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Why does paper fold so well?

bbc.co.uk

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Re: Why does paper fold so well?

#61

Post by srean »

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…

Yes it will be a catenary but it is not a problem if the purpose is to mark the ground.

If the purpose is also to measure the distance between the 'pegs' and one uses the length of the cable in between, then it can be a problem. That's why survey chains are expensive.

If we get real picky, no physical method will really be accurate because straight line is a mathematical abstraction. It can only be approximated in the physical world, much like a circle.

Light paths come closest, although they 'bend', they bend in a way that is 'straight' with respect to space-time.

Re: Why does paper fold so well?

#62

Post by srean »

Cthulhu_ wrote: post #60
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...

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.

Early humans fill me with awe with their ingenuity.

Consider the planets. They noticed that among thousands of stars these five move funny. Of course it helped that most of them are very bright and don't twinkle. On a clear sky even Sirius often doesn't twinkle though.

Re: Why does paper fold so well?

#63

Post by srean »

rolph wrote: post #57
dotancohen wrote: post #53

Earlier quoted context omitted.

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 com…

How do you calibrate the GPS

Re: Why does paper fold so well?

#64

Post by IAmBroom »

RetroTechie wrote: post #38
OJFord wrote: post #7

Earlier quoted context omitted.

I really can't imagine getting paper to sink any more easily than wood?

Try toilet paper. Let it into the water vertically as to not catch air pockets.

It floats, unless it is burdened with matter. Even when fully wet.

Re: Why does paper fold so well?

#65

Post by IAmBroom »

srean wrote: post #50
foobarian wrote: post #41

Earlier quoted context omitted.

One thing I find interesting about paper is that wetting and drying it turns it uneven. Even when drying it under a press. And then another ridiculous process not involving paper, but super cool nonetheless is creating a flat surface by grinding 3 not-flat objects against each other in round-robin manner.

I think wetting and drying of paper is a bit like heat treatment of steel. The fibres find a new local minimum stable position, prompted by the swelling and the shrinking.

Exactly. They were initially rolled, not merely pressed, which implies a longitudinal strain during the pressing moment.

Re: Why does paper fold so well?

#66

Post by rolph »

srean wrote: post #63
rolph wrote: post #57

Earlier quoted context omitted.

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 com…

How do you calibrate the GPS

there is a sattelite network, and a terrestrial reference station infra

Re: Why does paper fold so well?

#68

Post by rolph »

srean wrote: post #67
rolph wrote: post #66

Earlier quoted context omitted.

there is a sattelite network, and a terrestrial reference station infra

Yeah but how do we know there distances accurately

usually laser ranging is used to establish a baseline, rather than using a theodolite and chain like OG surveyors.

the rest is trigonometry, withe the GPSS defining points relative to the baseline.

https://www.gps.gov/trilateration

https://apps.dtic.mil/sti/html/tr/ADA165932/index.html

https://app.studyraid.com/en/read/15241/528230/determining-d...

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