efficiencies

Efficiency is a measure of how effectively a system converts input resources into useful output. The term spans multiple domains and is usually expressed as the ratio of useful output to total input, often as a percentage. Efficiencies can apply to energy, mechanical systems, processes, and economic decisions. It is different from effectiveness, which focuses on achieving intended goals regardless of resource use.

In physics and engineering, several specific notions exist. Energy efficiency refers to delivering the same service with less energy; mechanical efficiency is the ratio of useful work to total work supplied, accounting for losses such as friction and heat. Thermal efficiency applies to heat engines, defined as work output divided by heat input. Electrical efficiency is the ratio of electrical power delivered to the load to the electrical power supplied by the source.

In economics and operations, efficiency concerns optimal resource allocation and process performance. Economic efficiency considers whether resources are allocated to maximize social welfare, while operational efficiency focuses on reducing waste and cycle times in production and service delivery.

Measurement and limits. Efficiency is context-dependent and requires a clear definition of input and output. In thermodynamics, the second law imposes fundamental limits, such as the Carnot efficiency. Practical systems typically exhibit efficiencies well below theoretical maxima due to losses, design constraints, and cost trade-offs.

Applications. Improving efficiency is a common objective in energy policy, engineering design, manufacturing, and environmental management. Examples include upgrading insulation, adopting energy-saving technologies, and optimizing processes through lean principles.