Which of the following quantities is not conserved? A. Momentum B. Entropy C. Angular momentum D. Energy
The Correct Answer and Explanation is:
The correct answer is B. Entropy.
Explanation:
In physics, conservation laws describe quantities that remain constant in a closed system over time, provided no external forces or energy are added or removed. Let’s examine the options one by one:
A. Momentum:
Momentum is a conserved quantity in all isolated systems. According to the law of conservation of momentum, the total momentum of a closed system remains constant if no external forces are acting on it. This holds true for both linear momentum (in straight-line motion) and angular momentum (in rotational motion).
B. Entropy:
Entropy is not conserved in a closed system, except in ideal, reversible processes. In real-world situations, entropy tends to increase due to the Second Law of Thermodynamics, which states that the entropy of an isolated system will always either increase or remain the same, but never decrease. This law explains why certain processes are irreversible, like the mixing of gases or heat flowing from hot to cold bodies.
C. Angular Momentum:
Angular momentum, like linear momentum, is also conserved in a system with no external torque. This is a key principle in rotational motion. For example, when an ice skater pulls in their arms, they spin faster because angular momentum is conserved, even though their rotational speed changes.
D. Energy:
Energy is another conserved quantity in physics, according to the law of conservation of energy. In a closed system, energy cannot be created or destroyed, but it can change forms (kinetic, potential, thermal, etc.). However, this is true only in the absence of external work or energy losses (like friction or heat dissipation).
In summary, entropy is the only quantity listed that is not conserved, because it typically increases in real processes according to the Second Law of Thermodynamics.
