GED Science TestPhysical ScienceHard
A car engine operates by burning fuel, which converts chemical energy into mechanical energy to move the vehicle. During this process, a significant amount of heat is also generated and dissipated. Which fundamental principle of physics best explains why not all of the chemical energy is converted into useful mechanical energy?
- ALaw of Conservation of Mass
- BArchimedes' Principle
- CNewton's First Law of Motion
- DSecond Law of Thermodynamics
Show answer & explanationAnswer & explanation
Correct answer: D. Second Law of Thermodynamics
The Second Law of Thermodynamics states that in any energy transfer or transformation, some energy is always lost as unusable heat, increasing the entropy of the universe. This explains why no energy conversion process can be 100% efficient.
Why the other options are wrong
- A. The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction; it doesn't address energy efficiency.
- B. Archimedes' Principle describes buoyancy, which is unrelated to energy conversion efficiency.
- C. Newton's First Law (inertia) describes motion but not energy conversion efficiency.
Second Law of Thermodynamics
States that the total entropy of an isolated system can only increase over time, or remain constant in ideal cases. This implies that heat cannot spontaneously flow from a colder body to a hotter body, and that all energy transfers result in some energy being lost as unusable heat.
- Entropy (disorder) tends to increase.
- No energy conversion is 100% efficient.
- Heat always flows from hot to cold naturally.
Memory trick: Thermodynamics tells us about energy's flow, how it's conserved, and where it can't go.