function dy=move0(t, y)
dy = zeros(3,1); % force a column vector
dy(1) = 0.5; % dv/dt = acceleration, y(1) is velocity
dy(2) = y(1); % dx/dt = v,           y(2) is position
dy(3) = y(2); % ds/dt = x,           y(3) is integral of position
