[Sidefx-houdini-list] Gravity in Pop

Andy Nicholas andy at andynicholas.com
Sat Aug 22 19:34:10 EDT 2009

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
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