is there Air Resistance in AR?

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is there Air Resistance in AR?

Postby dudiobugtron » Wed Sep 27, 2006 8:25 am

Initially I thought that there wasn't any air resistance in Armadillo Run, and that the 'cloth parachute' efect was caused by some other weird physics. But I was talking to someone else who seemed pretty sure it was a simulation of Air resistance.

So I tried it out (see attached file):

The results I got show that there is a really basic air resistance - different materials fall faster or slower than others. But it isn't based on surface area/etc or anything else which might affect air resiustance in real life - it is just based on the different materials. The order of falling acceleration is below:

Armadillo (fastest)
Rubber
Metal Bar
Metal Plate
- big gap -
Elastic
Rope
Cloth (slowest)

Why does a horizontal metal plate fall faster than a piece of rope?


There is one other air-resistance like effect, which sees the endpoints of cloth objects bending down (although I think the overall centre of gravity stays the same)


Anyway, I'm sure many of you have tried a similar thing, but even if you haven't, what are your thoughts? is it 'air resistance' or some other phenomenon?
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drag race.lvl
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Postby ?rjan Flatseth » Wed Sep 27, 2006 10:48 am

I think it is just that different materials are delt with a litlte difference in gravity - to make it look a bit like there are air resistance. To actually simulate air-resistance would be 214 times more complicated I guess. The explanation of the ending points at horizontal cloth, elastics and rope falling faster - is that the endingpoints are exposed to a litle higher "gravity". Another question. Is it more likely that the Armadillo lifeform was created by "Peter Stock", or that it has develloped step by step from litle primitive pixels in the dawn of dillos? (about mars2006) :shock:
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Postby dudiobugtron » Wed Sep 27, 2006 10:10 pm

The other thing to note in this is that the force doesn't increase the speed of that metal bar construction falling. How can the force create rotational acceleration, but no acceleration up or down?
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Postby RaDiuM » Mon Oct 09, 2006 12:23 am

Once and for all I will proof that there is no Air resistance in this game :P
here ya go! :wink:
All similar objects even if their Air resistance (their size) are high or low they are always in the same speed.

(See Attachment :arrow: )

BTW i'm new to armadillo :D hello armadillo players!
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No Air Resistance.lvl
This is showing that there is no air resistance..
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Postby Mathias-san » Sat Oct 14, 2006 11:40 pm

Actually you can use the cloth as a type of parachute :D
(see attachment)
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Parachuter!.lvl
Parachuting Dillo
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Postby Gravity » Sat Nov 11, 2006 12:28 pm

Air resistance is proportional to velocity, so the correct way to check it is not to have a "drag" race, it could very well just be that different materials have different accelerations due to gravity, but to check to see if acceleration slows down. That is, does the armadillo gain as much speed in the second half of his fall as he does in the first half? If so, then yes, there is an air resistance. If no, then there is no air resistance.

I don't think there is air resistance, I think certain materials just have different accelerations.
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Postby ?rjan Flatseth » Sat Nov 11, 2006 6:14 pm

The drag race has been done. The Cloth is some of the slowest falling material.
Surely there is no air nor air-resistance in AR. It is just different falling speeds plotted in to make it a bit like something like airresistance..
I have never looked closely but I think every falling material reach a top speed very soon - they dont accelerate for ever - perhaps this is ment to give a "feeling" of air resistance to? I think author of AR has kept it very simple - wisely - cause real air-r. simulation would have smoked my CPU :wink:
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Postby Drone_Fragger » Sat Nov 11, 2006 9:09 pm

I think it is in place to stop amazingly dumb machines. Think about it, You could drop a weight over a large distance and then the sheer velocitymight cause it to fall through the floor, or push the poor armadillo through a wall.

I do know, however, that it is possible to force things to go above their max speed if you use a load of compressed rubber in a semicircle (like half an oragnge) That will fire the armadillo about 4 times its top speed. It does slow down to its normal max speed rather fast however. (about 2 seconds, which is enough for it to travel over a 0.75X0.75 map :O
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Postby Gravity » Sat Nov 11, 2006 10:00 pm

?rjan Flatseth wrote:The drag race has been done. The Cloth is some of the slowest falling material.
Surely there is no air nor air-resistance in AR. It is just different falling speeds plotted in to make it a bit like something like airresistance..
I have never looked closely but I think every falling material reach a top speed very soon - they dont accelerate for ever - perhaps this is ment to give a "feeling" of air resistance to? I think author of AR has kept it very simple - wisely - cause real air-r. simulation would have smoked my CPU :wink:

Air resistance isn't that complicated, especially given in two-dimensions, I think it simplifies down to an exponential function that you can generalize over all the objects (since different object have different accelerations), and you can even factor in area as well.
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Postby dudiobugtron » Mon Nov 13, 2006 3:03 am

Gravity wrote:Air resistance is proportional to velocity, so the correct way to check it is not to have a "drag" race, it could very well just be that different materials have different accelerations due to gravity, but to check to see if acceleration slows down. That is, does the armadillo gain as much speed in the second half of his fall as he does in the first half? If so, then yes, there is an air resistance. If no, then there is no air resistance.

I don't think there is air resistance, I think certain materials just have different accelerations.


Hehe, that's an interesting concept of 'half'

However you are right that my test is not a particularly insightful one. As I now see it, there are two models:

1) the one you think is the case;
materials have different (constant) accelerations. They accelerate (a) forever, or more likely, (b) until they reach a preset velocity (thanks ?rjan ;) )

2) the one you said that we need to check against;
there is an 'air resistance' which affects different materials differently, and is a function of the speed the material is going at. As a material accelerates, the air resistance increases, so overall acceleration decreases. The material stops accelerating when the upwards force from the air resistance is equal to the acceleration due to gravity.

Having thought about it, I now believe that model 2 is more likely. Anyone want to test it?
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Postby ?rjan Flatseth » Mon Nov 13, 2006 5:52 am

Hmm.. Yes perhaps some simple substitute for air resistance dont need to be that complicated - but a "true simulation" would be like estimating lots of chaotic turbulences and interferences between stuff and stuff - stash and stuff - stuff and stash -stash vs stash - and opposite :wink: .I guess some meteorology software to a couple of millon ? would add a cool touch to the game :lol: But of course as you say - its 2D anyway :shock:
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Postby the shizzle » Mon Jan 29, 2007 10:31 am

There is no air resistance in armadillo run. It is simply that each type of material has a different weight. the only real way to test air resistance is to create a parashoot and then test it with and withought the cloth for the shoot. i have done this and the drop times where exactly the same proving that armadillo run has no air resistance. it has gravity and each material has a specific gravitational pull i.e. weight.
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Postby JohnnyRoastbeef » Fri Aug 10, 2007 2:46 pm

Gravity wrote:
?rjan Flatseth wrote:The drag race has been done. The Cloth is some of the slowest falling material.
Surely there is no air nor air-resistance in AR. It is just different falling speeds plotted in to make it a bit like something like airresistance..
I have never looked closely but I think every falling material reach a top speed very soon - they dont accelerate for ever - perhaps this is ment to give a "feeling" of air resistance to? I think author of AR has kept it very simple - wisely - cause real air-r. simulation would have smoked my CPU :wink:

Air resistance isn't that complicated, especially given in two-dimensions, I think it simplifies down to an exponential function that you can generalize over all the objects (since different object have different accelerations), and you can even factor in area as well.


The simple form of air resistance on a body falling is just

constants*Ac*V^2

where you've got the cross sectional area and the square of the velocity. The problem with putting it in the game is with making it look real. Sure you could calculate the cross sectional area and the velocity, but falling plates with tilt will get a little bit of an airfoil effect and develop a horizontal velocity component as well. Try dropping a piece of paper and see how it behaves. There's instability to it and the force doesn't always act in an easily predictable direction. And what happens when you try to calculate it for a flexible material like the cloth? Now you need integrals to figure out the result. It's either put air resistance in and have it be very (a) complicated or (b) unrealistic, or make a simulated air resistance that gives pretty realistic results unless you look too closely at it. AR goes with the latter.
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Postby NeXFerret » Fri Aug 10, 2007 4:26 pm

WEIGHT DOES NOT AFFECT RATE OF FALL!

Drop an aluminium and lead cannonball in the same instant. They should hit the ground at exactly the same time if they are exactly the same shape.
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Postby JohnnyRoastbeef » Fri Aug 10, 2007 4:39 pm

NeXFerret wrote:WEIGHT DOES NOT AFFECT RATE OF FALL!

Drop an aluminium and lead cannonball in the same instant. They should hit the ground at exactly the same time if they are exactly the same shape.


I think if you study a little more physics you'll find that on earth, in the presence of atmosphere, weight does affect the rate of fall.

Sum F = m a right?

In the case of falling objects in the absence of air,

Code: Select all
-m g = m a
=> -g = a (minus indicates down toward the ground)

The mass cancels out, and the time it takes the object to fall is t=sqrt(2h/a), it doesn't depend on mass. With air resistance, it's more complicated.

Code: Select all
Fd - m g = m a


but Fd, the drag force, is:

Code: Select all
Fd = 1/2 * density * drag-coefficient * Ac * vel^2


so now, solving for the acceleration:

Code: Select all
a = 1/m * (1/2*density*drag-coefficient *Ac * vel^2) - g


The mass doesnt cancel out of the first term. And you've got a square in the velocity. That makes the solution for position what they call a non-linear differential equation. Very difficult to solve for the movement of the object.
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