Thermal Energy and Heat Transfer

By the end of this lesson, you will be able to explain thermal energy and temperature, apply specific heat capacity, describe the three heat transfer mechanisms, and state the Laws of Thermodynamics.

Temperature and Thermal Energy

Temperature: average kinetic energy of particles.

Thermal energy (internal energy): total KE of all particles.

Heat ($Q$): energy transferred due to temperature difference.

$Q = mc\Delta T$ where $c$ = specific heat capacity.

Water: $c = 4184$ J/kg·°C (very high — explains moderate climate near oceans).

Heat Transfer Mechanisms

Conduction: transfer through direct contact; metals are good conductors; wood, air are insulators.

$Q/t = kA\Delta T/L$ (Fourier's Law)

Convection: transfer by fluid motion; heated fluid rises, cooler fluid sinks.

Examples: heating a room, ocean currents, weather patterns.

Radiation: transfer via electromagnetic waves; no medium needed.

$P = \varepsilon\sigma A T^4$ (Stefan-Boltzmann Law)

All objects above absolute zero emit radiation.

Laws of Thermodynamics

Zeroth Law: if A and B are each in thermal equilibrium with C, then A and B are in equilibrium with each other. (Defines temperature.)

First Law: $\Delta U = Q - W$ (energy conservation: internal energy change = heat added − work done by system).

Second Law: entropy of an isolated system increases (or stays constant). Heat flows spontaneously from hot to cold; you can't build a perfect heat engine.

Third Law: entropy approaches a constant minimum as temperature approaches absolute zero.

Summary

Temperature: average KE; Thermal energy: total KE; Heat: energy transfer.

$Q = mc\Delta T$; specific heat capacity determines resistance to temperature change.

Heat transfer: conduction (contact), convection (fluid flow), radiation (EM waves).

First Law: $\Delta U = Q - W$ (energy conservation).

Second Law: entropy increases; heat flows hot → cold.