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Dark Physics & Dark A.I. & Dark Dynamix / defying the laws of gravity?

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mm0zct
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Posted: 26th Jul 2008 02:15
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I haven't used dark physics but i was rather disturbed to read in the recent newsletter:
Quote: "
"This will create a typical sphere in DBPro and allow physics gravity to take control of it. Now change the size of the sphere to 1 and see the difference in how quickly it picks up speed during the decent.""


surely the size of the object should not effect it's rate of acceleration?!

gravity accelerates everything at the same rate, the only effect "size" could have is on the effect or air resistsnce. if this is the case it should be object density not size that effects the object's maximum verocity. a tiny ball bearing will reach a higher speed than a giant polystyrene boulder. But a brick would reach a higher maximum speed than a feather.

please tell me "size" in the dbp sense does not effect the gravitational acceleration applied to it?

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BiggAdd
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Posted: 26th Jul 2008 04:16 Edited at: 26th Jul 2008 04:18
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While that may be true in a vacuum, Its not true in Air. PhysX may include some rudimentary drag calculations.

Like:
D=-1/2pV^2ACv, with an approximate calculation for the drag coefficient.

F=Ma
a=(F-D)/M

Therefore the acceleration will be decreased with more drag. (As you can see, in a Vacuum, D=0 and therefore a=F/M, As F is the weight of the object, a=acceleration due to gravity)


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mm0zct
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Posted: 27th Jul 2008 04:24
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that's why i was talking about drag/terminal velocity, but that's not going to make "bigger" things accelerate faster.

somewhere it is making the assumptions about the density / mass to surface area ratio of the object and the atmosphere which it is in, shouldn't it let you easily set these attributes if it's not going to assume it's a vacuum?

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BiggAdd
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Posted: 27th Jul 2008 05:10
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Quote: "that's why i was talking about drag/terminal velocity, but that's not going to make "bigger" things accelerate faster"


I've actually just ran a test. It seems no drag calculations are done.
All size shapes fall at the same rate.





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dark coder
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Posted: 27th Jul 2008 06:22
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Well it does say "see the difference in how quickly it picks up speed during the decent", so maybe it means the apparent rate of movement, which for a smaller object will be more apparent, whereas for a giant object, while it may well fall the same speed at any time as a small one, from a distance where you can see it, it would barely appear to move, who knows?

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BiggAdd
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Posted: 27th Jul 2008 06:51
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Quote: "Well it does say "see the difference in how quickly it picks up speed during the decent", so maybe it means the apparent rate of movement"


You are probably right there.


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mm0zct
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Posted: 29th Jul 2008 04:21
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ah thanks for clearing that up
my faith in physx/dbp is restored

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Nano brain
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Posted: 14th Aug 2008 00:47
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Phewww....heheh.
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General Reed
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Posted: 17th Aug 2008 14:11
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So your saying if one drops a pea it decends at the same rate as a baseball? Obviously if something is heaver, it will be pulled more toward the centre of gravity.

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BiggAdd
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Posted: 17th Aug 2008 16:52
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A pea and a baseball will fall at the same rate in a vacuum. Due to the air resistance on Earth, this is not so.

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