function dq = golf(q)

x = q(1);
y = q(2);
dx = q(3);
dy = q(4);
omega = q(5);

m = 0.046; % kg
r = 0.021; % m
Cd = 0.2; % dimensionless
S = 2e-5; % Magnus effect coefficient
rho = 1.2; % density of air, kg/m^3
A = pi*r^2; % cross sectional area

vvec = [ dx; dy ];
v2 = dot(vvec,vvec);
v = sqrt(v2);

FG = [ 0 ; -m*9.8 ];
FD = 0.5 * Cd * rho * v2 * A * (-vvec / v);
FL = S * omega * [-dy; dx];

avec = (FG + FD + FL)/m;
ax = avec(1);
ay = avec(2);
dq = [ dx; dy; ax; ay; 0 ];