function xdot= tennis1p(t,x)
global g alpha w etha
v = sqrt(x(3)^2 + x(4)^2);
Cd = (0.508 + 1/(22.503 + 4.196*(v/w)^0.4))*alpha*v;
Cm = etha*w/(2.022*w + 0.981*v)*alpha*v;
xdot = [ x(3)
         x(4)
         -Cd*x(3) + Cm*x(4)
         -g-Cd*x(4) - Cm*x(3) ];

