Does Cloth Room Gravity match Earth Gravity?

In short, I took a piece of cloth, turned it into lead, disarmed all air effects, dropped it from a height and measured positions at all frames. This gave me velocities, and acceleration.

Earth gravity acceleration is sort of a constant. Converting 1 sec to 30 frames gave the Poser equivalent. Measured acceleration and (converted) Earth acceleration were the same, within (5%) measurement accuracies. 0.01092 vs 0.01089, less than half a percent difference anyway.

This implies that we safely can get our rulers, scales and books out, to obtain values for Poser Cloth parameters. 

By the way, I just found out that the best website ever on Poser cloth, in the good old days that was: www.poserfashion.net, has disappeared. I therefore found out that the main pages of that site, are in my Library. So I will do you a cloth parameters table.

In long.

Piece of cloth is the hires square, raised to 19,6 mtr to give it exactly 2 sec = 60 frames for impact on the ground at 9,8 m/s^2 Earth gravity. Sim is set accordingly, all collision options switched off. Cloth parameters were set to max, thats 1000 for fold / sheer and stress resistance, and 1 for stretch damping and cloth density. cloth / static / dynamic frictions were set to 0, as was air-damping.

Reality test: a pack of 500 sheets of office paper measures 5cm, so 1 sheet has a 0,1mm thickness. Lead has a specific density of 11340 kg/m^3, therefore a sheet of lead as thick as office paper will have a density of 1,1340 kg/m^2. A similar value can be obtained with a sheet five times as thick (half a mm) and a specific density of 2000 kg/m^3. This is what stone (as used in corn-mills) is about (all: wikipedia). So, now we know what density 1 stands for.

The sim was run and as expected, it took about 60 frames to hit the floor.
Then I used a box to measure positions per frame, I could find no other way to find out. This introduced some measurement errors, for rounding (3 decimals = mm only), for the Front Cam is not good in spotting falling horizontal cloth position (no mesh thickness) and because the sim artefacts coased irregularities at the cloth edges.
Then I calculated velocity, according to V(f) = [ H(f-1) - H(f+1) ] /2, H= height, V=speed, f= frame number. Note that when you take adjecent frames, you get the speed at halfway the frame which is a minor shift in time. This way is more accurate.
The I obtained acceleration the same way: A(f) = [ V(f-1) - V(f+1) ] /2. It varied a bit due to the measurment errors mentioned, but did not fall down so air resistance was taken out indeed, within accuracy.

Note that due to this method frames 1,2, 59 and 60 (impact) could not produre meaningful results for acceleration. The average result over all other frames read 0.01092 m/f^2. The measurement error was obtained as about 5%.
Thats in frames time. The sim was done at 30fps, so I checked whether changing the value in the Animation Window made a difference. It did not. For the sake of it, I checked whether the scale of the cloth made any difference. It did not. 

Earth gravity reads 9.800 m/s^s on the Earth surface. There are differences, it's 9.832 at the poles and 9.780 at the equator as the Earth is not a perfect ball, and it varies a bit with underground and surroundings too. But 9.800 is a decent average.

That value, converted to 30fps, equals to 0.01089. 

And although the measured value resembles more to the gravity found at the poles or in the Rocky Mountains than with Earth average, in my point we've got a match. 

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though