I'm having a bit of trouble understanding the concepts of momentum conservation. Lets say I'm standing on a frictionless surface and I throw a 3kg brick horizontally with a velocity of 4m/s. In this scenario I can see that I'm going to be repelled backwards at a velocity of 12/my mass in kg but lets say instead of throwing a brick I punch a wall. The normal force acting on my fist will repel me backwards and I will have a new momentum but how is momentum conserved here if the velocity of the wall remains 0? Does all the kinetic energy go into vibrating the molecules of the wall + the tiny amount of heat and sound produced or something?