# Inclined plane 3d-physic simulation

1. Nov 27, 2003

### shaolin

I try to program a 3d-physic simulation, with bouncy collisions, friction, etc. and i have a problems with splitting forces at an inclined plane. i know that

$$F_n = F_g * sin(\alpha)$$ and
$$F_p = F_g * cos(\alpha)$$

$$F_n$$ ... normal force
$$F_p$$ ... parallel force
$$F_g$$ ... gravity force

but i would need this in general, in 3d and working in every dircetion. i don't know the angle of my collosion, but a normal
$$\vec{n}$$.

$$\vec{F_n} = \bar{F_g} * \vec{n}$$

but i can't think of how to do the paralell force.
can anybody help?

2. Nov 27, 2003

### Staff: Mentor

I'm not sure what you're trying to do, but if $$\alpha$$ is the angle the inclined plane makes with the horizontal (and assuming gravity acts vertically):
$$F_n = F_g * cos(\alpha)$$ (directed out of the plane) and
$$F_p = F_g * sin(\alpha)$$ (directed down the plane)

3. Nov 28, 2003

### zarcon

I would normalize the vector from the point of impact to the center of mass of the colliding object. With a sphere, it should be simply the normal of the inclined plane.

The gravitational force tangential to the inclined plane will be the original graviatational force vector MINUS the Dot Product of the original gravitational force vector and the plane normal (magnitude) multiplied by the plane normal (direction).

(sorry if that is confusingly displayed - I am a bit clumsy with this message stuff...)

But it is easy enough to work out on a sheet of paper...

try to avoid using any sines or cosines etc...