Algodoo's 2 Dimensional Pressure Standard

[xplane80]

I was wonder the other day:

How can you measure pressure with only 2 dimensions? Because P = f/a

So why do we make the 2D equivalent of Pressure. We can measure the Force (Newtons) and the Length (Meters) so:

F/L = (2d)P

And the standard should be like APU (Algodoo Pressure (2d Pressure) Unit) or something a little more complicated like this:

Sqrt( N*((6/7)^2)/m ) = 1 Gnr

So what do you think?

[RA2lover]

nice, but a slightly rotated box(or even a circle) will deliver too much pressure.

[xplane80]

With a box that would be true but a circle could be different e.g:-

Width of the pressure = (Diameter/√2)*(2/3)
E.g. a circle with a diameter of 1m would and have a mass of 1kg would exert:
9.81N/0.4714m = 20.8106 (~20.8) Apu or 3.910146(~3.9) Gnr.

1 meter square with a mass of 1kg would exert:
9.81N/1m = 9.81 (~9.8) Apu or 2.6847 (~2.7) Gnr.

With a quadrilateral you could say that each corner is 1/1000th of the mean diameter (√Area) e.g.

A rhombus' sides are 3m and the angles are [60, 120, 60, 120] thus the area is 2*((9√3)/4) and the mean diameter = 2.79181m so 1 corner would be 0.00292m (2.92mm).

[xplane80]

Here is a conversion table here:-

1 Apu = √Pa
1 Apu = 0.857143 Gnr
2 Apu = 1.212183 Gnr

1 Gnr = 1.361111... Apu
2 Gnr = 5.444444... Apu

1 atm = 318.31588 Apu ≈ 15.3 Gnr
1 bar = 316.227766 Apu ≈ 15.242 Gnr
1 psi = 83.022469 Apu ≈ 7.81 Gnr
1 Pa = 1 Apu = 0.857143 Gnr
2 Pa = √2 Apu = 1.01932 Gnr

Gnr => Apu

(Gnr^2)/((6/7)^2) = Apu

Apu => Gnr

(Apu*((6/7)^2))^0.5 = Gnr

[xplane80]

This is kind of a bump but if we have pressure then we would have stress and this means you would have to show this in someway or another.

Instead of stress being:

Fn/A

because Algodoo/Phun only has 2 dimension it should be:

Fn/L (L is length) or √(Fn/A)

[davidz40]

Generally good idea, but like Ra2Lover said, corners could create very high (infinite, to be exact) pressures. And assuming that corners have some length is really weird and doesn't fit into physics simulation for me.

[xplane80]

Yeah but in real life, there is no such thing as a perfect corner so it wouldn't be infinite.

[Antotabo]

In 2D simulation, like you said, pressure is measured on a length.

This happen because we assume that all body have the same thickness. So in the area calculation A=Lenght*Thickness, We give a constant value like 1, so it become: A=L*1 Or A=L.

But, to introduce element of 3D, you could give different Thickness values on the different body. For example; the air friction coefficient of individual body is a kind of thickness variable. The value mean that this particular body, have a relative thickness of ... compared to others. But this variable only have an effects on aerodynamic thickness.

Maybe This could be a cool suggestion: Add a thickness parameter on body. This would allow to go further and to enhance the simulation of real life physics.

Thickness would have an influence, solve problems of, or enhance :

- Aerodynamic or air friction thickness : Thicker body = larger forces. Air friction coefficient value that can be changed individually without changing thickness (like it is in Algodoo now) is unreal; For example; On an air plane if you put wider wings for added lift, then the wings would be heavier.

-Weight : Thicker body = more heavy . Weight would then be the real density units like kg/cubic M and weight would become the real life formula: Mass= density * volume = density*length*length*thickness

-Air, and Water buoyancy: This would allow more buoyancy realism, an example: A thicker body, would not float more itself in term of water line level (because as you increase buoyancy forces, you increase weight proportionally), but you could add a lot more weight on this body before it sinks.

-.....And many other glitches and misscomprehension of units.

-Also, if the Algodoo program get better, like if they implement stress or aerodynamic or... This would become Necessary.

Dam, as I wrote this, I realize that this is really something missing and/or wrong in Algodoo.

In sum, this would solve all your 3d to 2d calculation problem and it would let you use real good old formula like P=F/A or M=Density*V ..... Then no need to create special unit like APU .

[KarateBrot]

I don't think it's a good idea for a 2D physics simulation. If there's thickness it's just there. It's a number that affects the behaviour of geometries but you can't see any differences in the geometry shape no matter how thick a geometry is.
3D to 2D calculation isn't really a problem. It's very easy to achieve. Far from it: it's way more easy if you only have 2D instead of 3D. And there's no need and there never was a need to create a special unit like APU or something weird. Why trying to make it complicated if it's more easy with SI-units which already is the standard?

[Antotabo]

If this is not correct for 2D, then air friction isn't either, its worst. And I recommend that the thickness would be like air friction value: Normally set to 1, so absolutely nothing change in the gameplay if you don't wanna.

This is just like the original collision set idea suggestion in Phun, at first, people where saying that its not a good Idea because you can't see it.

This would not be complicated, it would be simpler in fact and a minor adjustment in the program.

And I know KarateBrot that you are more than enough bright to know that some calculation, or units are unachievable without the third dimension, like the pressure. I'm completely with you with the fact that creating new unit is a bad thing and that SI is the way to go. This is a solution for us to not do this.

I hope that this post can change your mind about that because I like you Karate and I would like your support .

[KarateBrot]

I hope that this post can change your mind about that because I like you Karate and I would like your support .

Thanks, I appreciate it^^

But still you also can simulate air friction in 2D correctly. I discovered that it's not correct in algodoo when I made calculations for an artillery projectile but that's because of another reason.
Even air friction get's much easier in 2D. In 3D you have to get the area of the shape that's projected on a plane in the direction of velocity (like the area of a shadow that's projected on a plane in the direction of the light). In 2D this siplifies to a simple line but still you can calculate it correctly.

[Antotabo]

And what about if you want more friction on a particular object? how would you make the air friction difference between a rectangle that represent a 4' x 8' x 1/2'' plywood viewed on the side, and a 8' long 1/2''x 1/2'' ? And when those shape floats what happen? They can carry the same mass? And how can you give a mass to something that have no volume to contain that mass?

[KarateBrot]

If you want to make the friction different just adjust the air friction coefficient. Of course there's a constant thickness of 1 meter in algodoo to calculate everything but if it can be adjusted they directly can make it 3D and there's no more need for a 2D view.

[guyboy]

At the moment phun doesn't really simulate 2d physics, it simulates a 2d projection of simplified 3d physics, assuming all objects have the same depth... I fully support a "depth multiplier" maybe not directly accessible through the GUI, but hidden in the script menu. 2d physics would be very different from 3d physics, like for example, in 2d the gravity falloff would be linear instead of quadratic.