How to calculate acceleration

[adam77]

I'm trying to get the acceleration of a given object at a given moment in time.
Does anyone have any tips on how to do this?
Is there a property, or would I have to calculate it from velocity?

Thanks.

[stooch]

I'm trying to get the acceleration of a given object at a given moment in time.
Does anyone have any tips on how to do this?
Is there a property, or would I have to calculate it from velocity?

Thanks.

you get a vector from subtracting the current position from the last. the length of this vector is your velocity at that point.
acceleration is the change of velocity, so you would want to sample more than one frame back if you want to establish a trend.

[RBD]

I'm just curious, since I don't really understand the need... rigid bodies have a constant velocity unless a force acts upon them, such as gravity or an other additional user specified force. Therefore, the only acceleration happening is the sum of the force vectors you are applying to an object, which you should already have.... No? Or are you are trying to calculate deceleration caused by friction and/or damping? If you could explain the problem, thanks.

[adam77]

yes i want decelaration as well

for any 2 arbitrary points in time i want the avg. acelaration or deceleration, i just wondered if there was a shortcut to avoid sampling the velocity and calculating myself

[RBD]

Ok, makes sense, thanks. (sorry, didn't mean to come across as critical; I thought I was missing something).

[bkate]

So, have we determined that sampling is the only way to get the current linear and angular acceleration of a body?

[adam77]

As far as I know, yes.