Oscillation criteria for nonlinear second order differential equations with damping

Using the integral average method, we give some new oscillation criteria for the second order differential equation with damped term (a(t) Psi(x(t)) K(x'(t)))' + p(t) K(x'(t)) + q(t) f(x(t)) = 0; t >= t(0). These results improve and generalize the oscillation criteria in [ 1], because they eliminate both the differentiability of p(t) and the sign of p(t), q(t). As a consequence, improvements of Sobol's type oscillation criteria are obtained.