[Coda]

No, change in energy per unit time is power, which is measured in watts. It's the P in P=IV. Voltage is change in energy per unit charge.

Yes, humans perceive changes in the kinetic energy of the eardrum as sound. However, if a tree falls in the wood, and no one is around to hear it, it still produces sound waves, so it's imprecise to describe sound as the way humans perceive kinetic energy.

The second sentence is the easier one. You're listing independent descriptions of the film. You could describe it as a "dark film" or as a "greasy film" without being wrong, therefore commas are appropriate.

The first sentence is more complex to analyze. The two descriptions aren't completely independent. You can drop "white" without damaging the sentence -- saying "middle-class Americans" would still be correct. However, if you were to say "white Americans" were affected, then you would be wrong, because poor white Americans (here the comma MUST be omitted to be correct!) were not affected due to not having TVs, and rich ones (notice that the pronoun "ones" replaces "white Americans" as a whole unit) were not affected due to already having access to everything they want.

I apologize for being imprecise. It doesn't require that there be more than one kind; that was meant as an example.