Final answer:
Machines transform energy from one form to another according to the law of conservation of energy, keeping the total energy in an isolated system constant.
Step-by-step explanation:
The law of conservation of energy is a fundamental principle in physics that applies to machines as well. This law states that within an isolated system, energy can change forms, such as from potential to kinetic energy, or be transferred from one object to another. However, the total amount of energy in that system remains constant. Therefore, when it comes to machines, option C is correct: Machines transform energy, but the total energy in a system remains constant. Machines do not create energy; instead, they convert it from one form to another, often doing work in the process. For instance, a car engine converts chemical energy from fuel into kinetic energy to propel the car forward. Similarly, an electric fan transforms electrical energy into kinetic energy to move air. These transformations and transfers adhere to the law of conservation of energy, ensuring that the energy within the system is neither created nor destroyed, but merely changed in form.