Energy comes in various forms, each with unique characteristics and applications. From kinetic energy of moving objects to potential energy stored in position, these forms play crucial roles in our daily lives and technological advancements.

Understanding energy conservation and conversion is key to grasping thermodynamic principles. As energy transforms from one form to another, it obeys the law of conservation, allowing us to analyze and optimize systems for better efficiency and resource utilization.

Forms of Energy

Forms of energy

• Kinetic energy
  • Associated with motion depends on mass and velocity of an object
  • Calculated using the formula $KE = \frac{1}{2}mv^2$ (moving car, flowing river)
• Potential energy
  • Stored in an object due to its position or configuration
  • Includes gravitational potential energy $PE = mgh$ and elastic potential energy (compressed spring, stretched rubber band)
• Thermal energy
  • Associated with random motion of particles in a substance
  • Depends on temperature and mass of the substance relates to internal energy of a system (hot coffee, molten lava)
• Chemical energy
  • Stored in bonds between atoms in a molecule
  • Released or absorbed during chemical reactions (gasoline, batteries)
• Electrical energy
  • Associated with movement of electric charges
  • Stored in electric fields or transported through electric currents (power lines, lightning)

Energy conservation and conversion

• Energy conservation
  • Cannot be created or destroyed only converted from one form to another
  • Total energy of an isolated system remains constant (pendulum, bouncing ball)
• Energy conversion examples
  • Kinetic to potential: roller coaster climbing a hill
  • Potential to kinetic: falling object (skydiver, avalanche)
  • Chemical to thermal: burning of fuel (campfire, gas stove)
  • Electrical to kinetic: electric motor (power tools, electric vehicles)
• Efficiency of energy conversion
  • No energy conversion is 100% efficient some always lost as heat due to friction or irreversibilities
  • Aim to maximize efficiency to conserve resources (LED lights, hybrid cars)

Energy transfer processes

• Work
  • Energy transfer through application of force over a distance
  • Calculated using the formula $W = \int F \cdot ds$ (moving a piston, lifting weights)
• Heat
  • Energy transfer due to temperature difference
  • Occurs through conduction, convection, or radiation (heating a pan, solar water heater)
  • Sensible heat transfer calculated using $Q = mc\Delta T$
• Mass transfer
  • Energy transfer associated with flow of matter into or out of a system
  • Carries energy in the form of enthalpy important in open systems (heat exchangers, turbines)

First law of thermodynamics applications

• First law of thermodynamics
  • Statement of energy conservation
  • Change in internal energy equals heat added minus work done: $\Delta U = Q - W$
• Closed systems
  • No mass transfer across system boundaries energy transfer limited to heat and work
  • Examples: sealed piston-cylinder device, closed refrigeration cycle
• Open systems
  • Mass transfer across system boundaries energy transfer includes heat, work, and mass transfer
  • Examples: steam turbine, gas compressor
• Problem-solving approach
  1. Identify the system and its boundaries
  2. Determine the type of system (closed or open)
  3. Apply the first law of thermodynamics, accounting for all energy transfers
  4. Use appropriate sign conventions for heat and work (positive for energy entering the system, negative for energy leaving the system)