The total amount of energy in the universe never changes, but the availability of each different type of energy to do work can change tremendously. What best explains this change in available energy?
a
Energy is always converted with 100 percent efficiency.
b
Energy is regularly changing from one form into another.
c
Energy can only be transferred as heat.
d
Energy can only be created through nuclear reactions.
b
Energy is regularly changing from one form into another.
This answer best captures the concept of energy transformation and its effect on the availability of energy to do work. When energy changes form, some of it often becomes less available for doing work because of entropy increase, which is a core principle of the second law of thermodynamics. For example, when mechanical energy is converted to thermal energy through friction, that heat energy is typically less ordered and less available to do useful work.