Conservation of Energy with Impact Problems

[imbackasd]

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So I understand that Energy cannot be created or destroyed etc, only transferred.

Now I am reading TBR and it states that in momentum collision problems Inelastic Collisions have Kinetic Energy being Not Conserved. Now my question is... If kinetic energy is not conserved and if the collision is on the same plane then doesn't that mean that Total energy ends up being not conserved? KEi is not = KEf (since PEi and PEf = 0 )

Or is it that total energy is conserved but the work of non conservative forces like friction take part? So would the equation be KEi + PEi + W = KEf + PEf ... with KE initial being more than KE final and so W compensating for that?

Just trying to sort this all out.

Thanks



EDIT:


Also in TBR it says that Elastic Collisions is defined by having conservation of energy and Inelastic collisions is defined by NOT exhibiting conservation of energy...I thought EVERYTHING has conservation of energy?

 

[milski]

It's converted to heat and potential energy (as deformations of the objects).

They mean conservation of kinetic energy. In a closed system the total energy is conserved - that is the sum of kinetic (linear + rotational) and all sorts of potential (mechanic, chemical, etc) energy.

 

[shaboobly]

energy is only conserved if there are no nonconservative forces, i.e. friction

 

[milski]

energy is only conserved if there are no nonconservative forces, i.e. friction

Energy is always conserved, you just need to include all the interacting objects in the system that you are talking about.