As the others have mentioned, momentum is conserved in a perfectly inelastic collision, but kinetic energy is not. Assuming that not all of the missing energy is lost to heat, sound or the deformation of the balls, a force will be present to hold the two balls together, so that they stick. The missing kinetic energy is converted to the potential energy associated with the force, which you might call the "binding energy" for the system.
bad_bird_karamaru t1_jczvl4k wrote
Reply to What happens if you throw 2 balls of equal mass and equal velocity at each other and they combine into one object? by minecraftmanyt
As the others have mentioned, momentum is conserved in a perfectly inelastic collision, but kinetic energy is not. Assuming that not all of the missing energy is lost to heat, sound or the deformation of the balls, a force will be present to hold the two balls together, so that they stick. The missing kinetic energy is converted to the potential energy associated with the force, which you might call the "binding energy" for the system.