A Simple Explanation of First and Second Laws of Thermodynamics

Thermodynamics is a very important subject of mechanical engineering in which lots of mechanical systems are designed and produced according to these laws. Thermodynamics deals with the calculation of energy. Not with the energy transfer mechanisms like heat transfer. With these strict calculations, lots of kinds of engineering systems are produced and developed such as internal combustion engines, refrigerators, air conditioners, etc. 

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So, thermodynamics is understanding energy. To be a very good engineer, you need to understand energy well. A very well understanding of energy starts with the first and the second laws of thermodynamics. Here, you can find very summary information about the first and the second laws of thermodynamics. 

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First Law of Thermodynamics

Actually, this is the simplest one. The total energy of the universe can not change. In other terms, energy is can not be created or destroyed to zero. You may think that when your battery runs out of energy, energy disappeared. No. The energy is converted into other forms of energy with your device. You may use a cordless drill with a 12V battery, when your battery running out of energy, you must assess that this energy is used as mechanical energy while you are tightening or unscrewing your screws or bolts of a mechanical system. 

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Here, you must understand the useful energy term. Your battery has useful energy or high-quality energy that can be converted to other forms of energy or works to make other works. To understand this high quality or useful energy, you must understand the second law of thermodynamics. 

Second Law of Thermodynamics

Energy has quantity and quality. The first law of thermodynamics expresses the quantity term of energy. The second law is about quality. The first law states the conservation of energy in which energy transforms into other forms of energy. The second law states that this conservation of energy is from high-quality energy to low-quality energy. Think about that you are tightening a screw with a cordless drill. While you are tightening it, you are using the useful energy in the battery. And this energy is stored as tight screw energy. Think about the quality of these two energies. 

You can use the high-quality energy in your battery in various kinds of mechanical works. But you can not use the energy stored in the tight screw. Also, an amount of energy is dissipated to surroundings, which is also stated as the efficiency of energy conservation. 


Understanding these basic principles of energy is very vital for an engineer, before starting thermodynamics. 

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