how do i keep a object from bouncing up and down or left and right?

guilleface

hi all i have a big square and inside some balls, i have the balls to change velocity to 100 related to actor and to collide with others balls and the wall, in the beginning every is ok but once i start destroying some balls, some of them get stuck moving up and down or left to right, what i need is when they collide with the ball to change direction to angle except 0,180,90 or 270 , thanks