Which of the following best describes hydraulic systems?

Hydraulic systems are fundamentally based on the principles of fluid mechanics, specifically utilizing liquids, most commonly oil or water, to transmit power. The definition provided by the correct choice highlights that hydraulic systems are influenced by the action of fluids, which is central to their operation. In these systems, the pressure applied to a confined fluid is transmitted undiminished throughout the fluid, allowing for the transfer of energy and force through components such as pistons and cylinders. This process enables hydraulics to be used in various applications, including machinery and automotive systems.

The other options do not accurately capture the essence of hydraulic systems. For instance, the use of solid materials would pertain more to mechanical systems rather than fluid-driven systems. While hydraulic systems involve energy transformations, they do not primarily convert mechanical energy into thermal energy. In fact, the efficiency of hydraulic systems relies on minimizing thermal losses. The mention of high viscosity fluids may not be universally applicable, as hydraulic systems can operate effectively with fluids of varying viscosities, depending on design and requirements. Therefore, emphasizing the influence of fluids provides a more accurate representation of how hydraulic systems function.