[Sidefx-houdini-list] Gravity in Pop

chris exarhos cexarhos at realimaginations.com
Sat Aug 22 19:39:56 EDT 2009


i should of said a change in velocity  :)

-----Original Message-----
From: sidefx-houdini-list-bounces at sidefx.com
[mailto:sidefx-houdini-list-bounces at sidefx.com]On Behalf Of chris
exarhos
Sent: Saturday, August 22, 2009 7:39 PM
To: sidefx-houdini-list at sidefx.com; andy at andynicholas.com
Subject: Re: [Sidefx-houdini-list] Gravity in Pop


actually...gravity is an acceleration, its a change in a constant
speed(velocity)

-chris

-----Original Message-----
From: sidefx-houdini-list-bounces at sidefx.com
[mailto:sidefx-houdini-list-bounces at sidefx.com]On Behalf Of Andy
Nicholas
Sent: Saturday, August 22, 2009 7:34 PM
To: sidefx-houdini-list at sidefx.com
Cc: sidefx-houdini-list at sidefx.com
Subject: Re: [Sidefx-houdini-list] Gravity in Pop



I wouldn't describe gravity as an acceleration. Gravity is a force like
any other, except that it's magnitude is proportional to the mass of the
object it's acting on.

F = G M m / r^2

Assuming M is constant (the Earth's mass), then since F=ma, the mass m
cancels from both sides giving the property of constant acceleration
independent of mass.

So, the short answer is yes, you're right, the shelf is wrong.

I tend to use "Override Mass" and set it to 1 though, as it's a bit
ambiguous what it does by ignoring mass. I'm guess it's doing that when
you ignore mass, but I like to be sure.





> Hi, a silly one :)
>
> Do I understand it properly? A force in real world react differently
> depending of the mass but since gravity is an acceleration, no matter
> the mass all objects should fall at the same speed. For that reason we
> must check "Ignore Mass" on a Force Pop to simulate gravity but when you
> create it through the shelf it is not checked by default. Who's wrong?
>
> François
> _______________________________________________
> Sidefx-houdini-list mailing list
> Sidefx-houdini-list at sidefx.com
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>


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