is mechanical energy conservative?
No, the mechanical energy of a system might, occasionally be conserved; "conservative"/non-conservative is a way to classify FORCES.
I assume you mean: Is mechanical energy conserved? Answer: Sometimes!
For example: A block sliding down a frictionless incline--mechanical energy (PE + KE) is conserved; but introduce friction, then mechanical energy is not conserved.
Did you have a particular situation in mind?
sliding a block on a flat table. I saw that there wasn't a change in Kinetic Energy. So, that means energy is not conserved. I know that the friction force is non-conservative but I wasn't sure about the mechanical energy.
Why would seeing the KE not change lead you to think that energy was not conserved?
Mechanical energy is not a force.
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