# Determining kinetic energy loss in inelastic collisions

I know there have been a lot of threads about this topic, but I haven't found one that answers my specific question. So if we have a case of two objects that stick together after colliding, with no external force present, then the momentum of the system is conserved. From that one can calculate the velocity of the combination of the two objects and use that to find the final kinetic energy (K.E.). We also know the initial K.E. as the sum of the K.E. of each object. The difference K.E.(final) - K.E.(initial) can be calculated and it is negative as some K.E. has been converted to heat. An example with equations can be found in @Bob D's answer here: Why do objects always stick together in perfectly inelastic collisions

What I'm wondering about is that it seems to me that if a variety of objects were used, all with different physical properties governing their deformation (elasticity, stiffness or whatever is appropriate), then that should affect how much K.E. is lost to heat. But the equations give one particular answer for K.E. loss. How do they "know" to do that without detailed knowledge of the objects' composition?

• Does this answer your question? Inelastic Collision and Kinetic Energy Commented Jul 27, 2020 at 21:28
• I didn't find my specific question addressed there. If it was, please point out where. Suppose the two objects were cotton balls, or pillows, or slabs of Jello or mechanical slinky toys, etc. It would seem that the loss of K.E. to heat and/or sound would be different in each case, yet the same loss of K.E. is calculated just based on their masses and initial velocities, without knowing what they are. Commented Jul 28, 2020 at 1:22
• The kinetic energy loss for a perfectly inelastic collision is unique and described in the answer to the linked question. However, you do still need to know the properties of the colliding objects in order to determine whether the collision will be perfectly inelastic. Commented Jul 28, 2020 at 4:24
• @Not_Einstein Look at ohw's answer . Kinetic energy depends on velocity and mass only. Commented Jul 28, 2020 at 4:59
• I am aware of the equations and so stipulated in my question. I am really after an intuitive understanding of how very different materials with different physical properties all manage to lose the exact same amount of kinetic energy (for given masses, initial velocities) to heat, sound, etc. when they stick together. Why is that K.E. loss unique? Commented Jul 28, 2020 at 13:29