Preface/Author’s Note

Thermodynamics is a particularly boring yet essential part of physics. A statement I am sure many college readers pursuing an applied physics field can relate to. I hope this article makes thermodynamics a bit more enjoyable.

What is Thermodynamics?

Thermodynamics is the branch of physics that studies energy, heat, and their transformations. It focuses on how energy moves between systems and surroundings, and how it changes form, such as from heat to work. Thermodynamics is guided by four main laws that explain concepts like energy conservation, entropy (disorder), and equilibrium. These principles apply to everything from engines and refrigerators to stars and biological processes.

0th law

The zeroth law of thermodynamics states if there are three objects in a system and the third one is in thermal equilibrium with object 1 and 2, then they are all in equilibrium. For objects to be in thermal equilibrium, their temperatures must be equal. 

Pretty simple so far.

1st law

The first law of thermodynamics has to do with the conservation of energy which strictly lays out the fact that energy can change forms but never be created or destroyed…never. A very simple example as to how it works is, a phone converts chemical energy (battery) to electrical energy to thermal energy which is radiated into the air, so on and so forth. If we rewind, the electrical energy for the phone to work comes from an energy plant whose energy can be traced back millions of years from carbon life that died millions of years ago.

2nd law

The second law of thermodynamics states heat transfers go from hot to cold, so a hot object will heat up a cooler one until they reach a point of equilibrium. For example, a hot cup of tea cools down because heat, in the form of water vapor, coming from the coffee heats up the air surrounding it. Similarly, water becomes cooler with ice in it because it is giving off heat to the ice in other words ice is “absorbing” energy.

Entropy

To proceed to the next law and to better understand the previous law it is necessary to understand what entropy is, as I’ve found that it is the most poorly explained word on the internet, where it is described as the state of disorder in a system. The given definition is a good concise definition but doesn’t give clarity to it being used in a thermodynamic context. Where it could be refined to say: Entropy is a value that quantifies the disorder of molecules in something. For example, when something is heated there is more kinetic energy produced by the molecules resulting in more entropy, and when something is cooled there is less kinetic energy produced by the molecules resulting in less entropy. But, what happens when something cools to absolute zero…that my friends is where the third law of thermodynamics comes in.

3rd law

The third law of thermodynamics states entropy approaches a constant value and temperature approaches absolute zero. In essence, it means that as a system gets colder, approaching absolute 0 (0 Kelvin), the motion or kinetic energy of particles slows until a point where entropy reaches the lowest possible value. When entropy is equal to 0 it means that there is only one possible state/arrangement the particles can be in.

IMPORTANT PLEASE READ:

To make these posts more interactive, I will start asking questions for my readers to answer in the comments.

Today’s prompt, type your answer below in the comments: 

What is your favorite field of engineering or physics?

I’ll Start: Aerospace Engineering