Question

How does friction affect the law of conservation of energy?

Answer 1

Law of conservation of energy is an exact law of nature. That cannot be violated. If you found some system violating this conservation by observing things, you can infer that your observation went wrong at some point.

Complete answer:
Law of conservation of energy states that, for an isolated system Total energy remains constant. That is energy can neither be created nor be destroyed but it can transfer from one form to different form.
Frictional forces may dissipate energy, that’s why this question arises, does it violate law of conservation of energy? The answer is No. in the act of friction what happens is Energy is transferring from one form to another. There will be no loss of energy.
In order to understand this problem let us take an example, Two buses crash into each other. After the crash the buses are no longer moving. Where does this energy go? The answer is quite simple, the friction between buses and in between bus and road allows the energy to transfer one form to another.
You may know that when we rub our hands together heat generates, what happens here is the frictional energy converting into heat energy. This is what happens in bus crashes, where due to friction and crash the energies can be converted to Thermal energy, sound energy or any other form of energy.
So that energy we thought we lost actually transferred to heat and sound. bus crashes are not only loud, but also generate a lot of friction on the ground and in the bent metal. Heat and sound are both forms of energy.

Note: Exact laws of nature cannot be violated. Law of conservation of energy is such a law. Friction always opposes relative motion between two contact surfaces.