1.1 Fundamental concepts and definitions

Thermodynamics is all about energy and how it changes. It's the science behind power plants, engines, and even your fridge. Understanding energy, work, and heat is key to grasping how things move and transform in the world around us.

Energy comes in many forms, from the motion of objects to the bonds in chemicals. The big idea? Energy can't be created or destroyed, only changed. This principle helps us figure out how machines work and how to make them better.

Introduction to Thermodynamics

Concept of thermodynamics

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Top images from around the web for Concept of thermodynamics

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  The First Law of Thermodynamics | Physics View original

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  The First Law of Thermodynamics and Some Simple Processes | Physics View original

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  Applications of Thermodynamics: Heat Pumps and Refrigerators | Physics View original

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  The First Law of Thermodynamics | Physics View original

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• Studies energy and its transformations focuses on relationships between heat, work, and other forms of energy
• Deals with conversion of energy from one form to another (mechanical to thermal, chemical to electrical)
• Applies to design and optimization of power generation systems (steam power plants, gas turbines, internal combustion engines)
• Used in refrigeration and air conditioning systems, heat exchangers and heat transfer equipment, fuel cells and renewable energy systems, aerospace and automotive engineering

Energy vs work vs heat

• Energy capacity to do work or cause change measured in joules (J) or other equivalent units
• Work energy transfer associated with force acting through a distance calculated as $W = F \times d$, where $F$ is force and $d$ is displacement
• Heat energy transfer due to temperature difference flows from higher temperature object to lower temperature object measured in joules (J) or calories (cal)
• Temperature measure of average kinetic energy of particles in a substance indicates hotness or coldness of an object measured in Kelvin (K), Celsius (°C), or Fahrenheit (°F)

Energy Forms and Conservation

Forms of energy

• Kinetic energy associated with motion
  • Translational kinetic energy $KE = \frac{1}{2}mv^2$, where $m$ is mass and $v$ is velocity
  • Rotational kinetic energy $KE = \frac{1}{2}I\omega^2$, where $I$ is moment of inertia and $\omega$ is angular velocity
• Potential energy associated with position or configuration
  • Gravitational potential energy $PE = mgh$, where $m$ is mass, $g$ is acceleration due to gravity, and $h$ is height
  • Elastic potential energy $PE = \frac{1}{2}kx^2$, where $k$ is spring constant and $x$ is displacement
• Internal energy sum of kinetic and potential energies of particles within a system
• Chemical energy stored in chemical bonds
• Electrical energy associated with flow of electric charges
• Electromagnetic energy associated with electromagnetic waves (light, radio waves)
• Interconversion of energy forms
  • Mechanical energy (kinetic + potential) converted to thermal energy through friction
  • Chemical energy converted to electrical energy in batteries or fuel cells
  • Electrical energy converted to mechanical energy in motors

Energy conservation in systems

• First Law of Thermodynamics energy cannot be created or destroyed, only converted from one form to another
  • Change in internal energy ($\Delta U$) of a system equals heat added ($Q$) minus work done by the system ($W$)
    • $\Delta U = Q - W$
• Closed systems no mass transfer across system boundaries
  • Change in internal energy depends only on initial and final states, not path taken
• Open systems mass transfer across system boundaries
  • Energy balance must account for heat and work interactions, as well as energy associated with mass flow
• Steady-state systems no change in properties over time
  • Energy entering the system equals energy leaving the system
• Isolated systems no energy or mass transfer across system boundaries
  • Total energy remains constant