Final answer:
The factor that reduces the total energy of an isolated system over time is D) Energy loss due to friction and heat, since it results in the dispersion of energy in non-recoverable forms, decreasing the system's usable energy.
Step-by-step explanation:
Isolated systems maintain the same amount of total energy, even though it may be transformed from one type to another. The factor that would reduce the total energy of this system over time is D) Energy loss due to friction and heat. This is because, in an isolated system, no energy is entering or leaving the system. Therefore, factors such as increasing energy input or adding an external energy source would not apply, as they would involve external interactions. Reducing friction within the system would not reduce the total energy; it would merely minimize the transformation of energy to non-useful forms. Energy loss due to friction and heat, however, directly correlates to energy being dispersed in forms that may not be useful to the system and cannot be recuperated, thus reducing the usable total energy of the system over time.
When considering how the total energy is affected, it's essential to recognize that the total energy of the system is the sum of its kinetic energy, potential energy, and microscopic internal energy. Transfers of mechanical energy into or out of the system, such as doing work on the system or transferring energy by heat, can also modify the total energy of the system. However, since we're discussing an isolated system, the total energy can only decrease through internal processes like friction and the resulting heat, not through external work or heat transfer.