function ydot = fallingf(t, y)
% FALLINGF :  derivative function for simplified falling body
%
% Second-order ODE: x'' = -9.81 + 0.01 (x')^2
% y(1) = x
% y(2) = x'

ydot = [ y(2) ; -9.81 + 0.01 * y(2)^2];