if(@Frame % 2){
    vector center = {0,0,5};
    vector pos ;
    pos = set(-(nrandom()-0.5),0,2);
    int pt = addpoint(0,pos);
    vector vel = set(0,0,-4*nrandom());
    setpointattrib(0,"v",pt,vel);
    setpointattrib(0,"m",pt,1);
    }

vector grad = volumegradient(1,0,@P);
vector dir_g = normalize(grad);
vector dir_v = normalize(@v);
int sig = sign(dot(grad,@v))*-1;
float strength = 5*(1-dot(dir_g,dir_v));
@force += strength *grad*sig;
if(@P.y >0)
@force.y += -1.98;
if(@P.y <= 0)
@force += 0.5*vector(onoise(@P));

@accel = @force/@m;

@v += @accel*@TimeInc;
@v  = clamp(length(@v),0.2,4)*normalize(@v);
@v.x= 0;
@P += @v *@TimeInc ;
@force = {0,0,-0.1};