Lecture Notes: Thermodynamics and the Drinking Bird

Introduction

• The Drinking Bird toy appears like a perpetual motion machine, but it's not due to physical laws.
• Perpetual motion is impossible according to physics.

First Law of Thermodynamics

• Main Goal: Describe the transfer of energy.
• Two key processes: Work and Heat.
  • Work done by a system results in heat loss.
  • Heat added to a system can do work.
• Internal Energy (U): Total kinetic and potential energy of all molecules.
• First Law Formula:
  • U = Q - W
  • Q = heat transfer, W = work done.
  • Signs:
    • Q > 0: Heat added.
    • Q < 0: Heat removed.
    • W > 0: Work done by system.
    • W < 0: Work done on system.

Conservation of Energy

• The first law restates the conservation of energy principle.
• Heat loss (e.g., through friction) prevents perpetual motion.

The Drinking Bird's Mechanics

• Depends on energy from water.
• The fluid inside has a low boiling point.
• Cycle:
  • Head dips and gets wet.
  • Water evaporation cools vapor, condenses into liquid.
  • Partial vacuum forms, liquid moves up.
  • Head dips back, cycle restarts.

Types of Thermodynamic Processes

1. Iso-volumetric Process

   • Volume constant, heat added/removed.
   • Pressure & temperature change.
   • No work done, only internal energy changes.

2. Isobaric Process

   • Pressure constant, volume changes with heat.
   • Can do work (e.g., moving a piston).
   • Work formula: Work = pressure x change in volume.

3. Isothermal Process

   • Temperature constant, system connected to heat reservoir.
   • Pressure changes, requires integration to calculate work.
   • No change in internal energy.

4. Adiabatic Process

   • No heat exchange, but gas can expand/compress.
   • Change in internal energy equals negative of work done.

Second Law of Thermodynamics

• Heat flows spontaneously from hot to cold.
• Entropy:
  • Describes disorder of a system.
  • Entropy increases in real-life scenarios.
  • When system entropy decreases, environment's entropy increases more.
  • Probability favors increases in entropy.

Entropy and Probability

• Shattered mug analogy: Many ways to be broken (high entropy), few to be whole (low entropy).
• Heat flow increases entropy.

Conclusion

• Reviewed the first and second laws of thermodynamics.
• Overview of isovolumetric, isobaric, isothermal, and adiabatic processes.
• Discussed entropy and its implications.

Further Resources

• PBS Digital Studios and affiliated shows.
• Crash Course production credits.