Chapter 15: Thermal Energy and Heat

Thermal Energy

The total kinetic energy of the particles in an object.

Heat

The flow of thermal energy from a region of higher temperature to a region of lower temperature.

Thermodynamics

The study of thermal energy and its transfer.

Kinetic-Molecular Theory

Thermal energy arises from the motion of particles. Faster motion corresponds to higher temperatures.

Caloric Theory

An outdated theory that described heat as a self-repelling fluid called caloric.

Evidence for the Kinetic-Molecular Theory

• Diffusion: Dye spreads faster in gases than in liquids, showing particle motion.
• Brownian Motion: Visible movement of particles provides evidence of molecular motion.

Development of Heat Theories

• Count Rumford disproved caloric theory through cannon-boring experiments.
• James Joule demonstrated the mechanical equivalent of heat, showing energy conservation.

Mechanical Equivalent of Heat

Mechanical Equivalent

$4.186 J=1 \mathrm{cal} (\mathrm{at} 15°C)$

Mechanisms of Heat Transfer

• Conduction: Direct transfer of energy between particles.
• Convection: Movement of thermal energy by fluids or gases due to buoyancy.
• Radiation: Transfer of energy through electromagnetic waves.

Questions for Students

1. Define thermal energy and differentiate it from heat.
2. What evidence supports the Kinetic-Molecular Theory?
3. Explain the mechanical equivalent of heat and its significance.
4. How did Count Rumford's experiments challenge the caloric theory?
5. What are the three mechanisms of heat transfer, and how do they differ?