a container shakeout apparatus is provided and has a rigid frame upon which a pair of motors supporting eccentric weights are mounted . spring reactor members are suspended from the frame and said springs in turn suspend a pair of hammers which are adopted to engage the top edge of the spaced sides of a loaded container such as a hopper car . the motors and eccentric weights form a single mass system having a natural frequency close to the operating speed of said motors when said hammers are in contact with the container ; and said frame , springs and hammers form a two mass system having a natural frequency above the operating speed of the motors when said hammers break contact with the container whereby the combined alternating single mass system and two mass system produce rapid high energy vertical impacts on the container for loosening material in the container .