Why heat never flows from cold to hot in our universe
In short: The first law of thermodynamics says energy is conserved, but it doesn't explain why certain processes never happen in nature. This video explores the second law and the concept of entropy to explain the direction of physical change.
While energy remains constant, the second law of thermodynamics dictates that the entropy of the universe constantly increases. To illustrate this, consider heat transfer: while it is theoretically possible for a cold object to heat up by drawing energy from a hot object without violating energy conservation, such a process never occurs in nature.
The video explains how scientists like Clausius, Kelvin, and Carnot developed different forms of the second law to describe these observations. It introduces entropy as a state variable where the change in entropy (ΔS) equals heat transfer (ΔQ) divided by temperature (T). In reversible processes, such as an ideal flow through a constricted pipe with no boundary layer losses, the entropy of the system and its environment remains constant.
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Sources
- Summary by Intellect · source: Second Law of Thermodynamics and entropy | Biology | Khan Academy
- Also: Second Law - Entropy | Glenn Research Center | NASA
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