Design Engineer Interview Question:

Explain the laws of thermodynamics and its importance of in Mechanical Engineering?

Submitted by: Muhammad

Thermodynamics is a physical science which studies the interrelation between heat, work and the internal energy of any system. Thermodynamics helps study all the systems of mechanical engineering. There are three laws of thermodynamics.

First Law: Energy can be neither created nor destroyed. It can only change forms. In any process in an isolated system, the total energy remains the same.

Eg: turning on a light would seem to produce energy; however, it is electrical energy that is converted.

Second Law: The second law of thermodynamics states that the entropy of any isolated system not in thermal equilibrium almost always increases.

Eg: A car that has run out of gas will not run again until you walk 10 miles to a gas station and refuel the car.

Third Law: As temperature approaches absolute zero, the entropy of a system approaches a minimum.

Eg: Water in gas form has molecules that can move around very freely. Water vapor has very high entropy (randomness). As the gas cools, it becomes liquid which can still move around but not as freely. At this point they have lost some entropy. On cooling further it becomes solid ice where molecules can no longer move freely but can only vibrate within the ice crystals. The entropy is now very low. As the water nears absolute zero, the vibration of the molecules diminishes. If the solid water reaches absolute zero, all molecular motion would stop completely. And at this point the water would have no entropy at all.
Submitted by: Muhammad