The second law of thermodynamics states that in any energy transfer or transformation, the total entropy of a closed system will always increase over time. Entropy is a measure of disorder or randomness, meaning that systems naturally progress towards a state of greater disorder. This principle explains why processes like melting ice or mixing hot and cold water occur spontaneously. In practical terms, the second law implies that energy conversions are never 100% efficient. For example, when a car engine burns fuel, some energy is lost as heat, contributing to increased entropy. This law has significant implications in fields like physics, chemistry, and engineering.