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# Forces

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Got a little question for you math-guys. Say I have a point A, which in this case is the centre of gravity of a car. If I then apply a force at another point B with direction D and size P how do I calculate the resulting positional and rotational forces on point A. This could for example be if we drive into something with the front left corner of our fantastic car. Hope you understand what I mean. Oh, another thing, I'm trying to do this in 3D. And I really suck at 3D-math. Any help would be greatly appreciated. Edited by - Lantz on October 19, 2001 8:15:46 PM

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Five years ago I could have helped you... but now instead of going to Physics class I just drink beer and play video games

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Damn. Anyone else?

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The vector from A to B is called the arm. The application of force at B results in a moment around A. That''s all I can remember (I drink Moutain Dew, though).

So look up vector moments.

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The cross product of a vector from the center of mass to the point of impact with a vector for the force applied is the torque. Well, actually I think the torque is the magnitude of the resulting vector. My physics is more than a bit rusty so I don''t know where you go from there.

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Hmm. I already think I know the principles and what I have to do. But I dont know how. I was hoping on some formulas.

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Okaayy...

|--------------|
| A |
|--------------B
^
/
/ P
The direction would be the same i think.
The force...crap...its been years.
What you need to do is look up levers. :-D
Thats basically whats going on, i think.

I came, I saw, I got programmers block.
~V''''lion

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So, you have:
A ----- B         \          \           D

First, find angle ABD = arcos((AB.BD)/|AB||BD|)
Now, translational forces are P(cos ABD) in direction AB and rotational forces are P(sin ABD) in direction perpendicular to AB

rotational forces can probably just be modelled as a rotational acceleration of P(sin ABD)/mass_of_car.

Not fully sure of anything, but hopefully someone will see this post and correct anything that''s wrong.

Hope that helps

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This is IMHO the best starting place on such matters: http://www.d6.com/users/checker/dynamics.htm
It has a series of 4 articles, explaining rigid body dynamics. It starts very simple in 2D with just lineair force effects, then handles 2D rotational effects of forces, 2D collision response impulses and then those same things in 3D.

Dirk =[Scarab]= Gerrits

1. 1
2. 2
Rutin
22
3. 3
JoeJ
18
4. 4
5. 5

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