2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/93643A conditional kinetic energy is defined in terms of the Wigner distribution. It is shown that this kinetic energy may become negative for negative Wigner distributions. A free particle wave packet with negative kinetic energy will spread in a nonclassical manner.To appear in proceedings of the 5th International Conference on Squeezed States and Uncertainty RelationsQuantum Physicstext