When mechanical energy is lost due to friction, it becomes energy. chemical thermal kinetic electrical?

Thermal

Explanation:

Here mechanical energy is defined as

Mechanical energy = Kinetic energy + potential energy

so here we know that mechanical energy is conserved when all forces on an object is conservative in nature

if we have non-conservative forces on the system then that will decrease the mechanical energy.

This decrease in mechanical energy is mainly due to different types of frictional losses

All these frictional losses are always in the form of thermal energy where we will have some heat loss