Skip to Content
College Physics for AP® Courses

# Section Summary

### 14.1Heat

• Heat and work are the two distinct methods of energy transfer.
• Heat is energy transferred solely due to a temperature difference.
• Any energy unit can be used for heat transfer, and the most common are kilocalorie (kcal) and joule (J).
• Kilocalorie is defined to be the energy needed to change the temperature of 1.00 kg of water between $14.5ºC14.5ºC$ and $15.5ºC15.5ºC$.
• The mechanical equivalent of this heat transfer is $1.00 kcal=4186 J.1.00 kcal=4186 J.$

### 14.2Temperature Change and Heat Capacity

• The transfer of heat $QQ size 12{Q} {}$ that leads to a change $ΔTΔT size 12{ΔT} {}$ in the temperature of a body with mass $mm size 12{m} {}$ is $Q=mcΔTQ=mcΔT size 12{Q= ital "mc"ΔT} {}$, where $cc size 12{c} {}$ is the specific heat of the material. This relationship can also be considered as the definition of specific heat.

### 14.3Phase Change and Latent Heat

• Most substances can exist either in solid, liquid, and gas forms, which are referred to as “phases.”
• Phase changes occur at fixed temperatures for a given substance at a given pressure, and these temperatures are called boiling and freezing (or melting) points.
• During phase changes, heat absorbed or released is given by:
$Q=mL,Q=mL, size 12{Q= ital "mL"} {}$

where $LL size 12{L} {}$ is the latent heat coefficient.

### 14.4Heat Transfer Methods

• Heat is transferred by three different methods: conduction, convection, and radiation.

### 14.5Conduction

• Heat conduction is the transfer of heat between two objects in direct contact with each other.
• The rate of heat transfer $Q/tQ/t size 12{Q/t} {}$ (energy per unit time) is proportional to the temperature difference $T2−T1T2−T1 size 12{T rSub { size 8{2} } - T rSub { size 8{1} } } {}$ and the contact area $AA size 12{A} {}$ and inversely proportional to the distance $dd size 12{d} {}$ between the objects:
$Qt=kAT2−T1d.Qt=kAT2−T1d. size 12{ { {Q} over {t} } = { { ital "kA" left (T rSub { size 8{2} } - T rSub { size 8{1} } right )} over {d} } } {}$

### 14.6Convection

• Convection is heat transfer by the macroscopic movement of mass. Convection can be natural or forced and generally transfers thermal energy faster than conduction. Table 14.4 gives wind-chill factors, indicating that moving air has the same chilling effect of much colder stationary air. Convection that occurs along with a phase change can transfer energy from cold regions to warm ones.

### 14.7Radiation

• Radiation is the rate of heat transfer through the emission or absorption of electromagnetic waves.
• The rate of heat transfer depends on the surface area and the fourth power of the absolute temperature:
$Qt=σeAT4,Qt=σeAT4, size 12{ { {Q} over {t} } =σeAT rSup { size 8{4} } } {}$

where $σ=5.67×10−8J/s⋅m2⋅K4σ=5.67×10−8J/s⋅m2⋅K4$ is the Stefan-Boltzmann constant and $ee size 12{e} {}$ is the emissivity of the body. For a black body, $e=1e=1$ whereas a shiny white or perfect reflector has $e=0e=0$, with real objects having values of $ee$ between 1 and 0. The net rate of heat transfer by radiation is

$Q net t = σ e A T 2 4 − T 1 4 Q net t = σ e A T 2 4 − T 1 4 size 12{ { {Q rSub { size 8{"net"} } } over {t} } =σeA` left (T rSub { size 8{2} } rSup { size 8{4} } - T rSub { size 8{1} } rSup { size 8{4} } right )} {}$

where $T1T1 size 12{T rSub { size 8{1} } } {}$ is the temperature of an object surrounded by an environment with uniform temperature $T2T2 size 12{T rSub { size 8{2} } } {}$ and $ee size 12{e} {}$ is the emissivity of the object.

Citation/Attribution

Want to cite, share, or modify this book? This book is Creative Commons Attribution License 4.0 and you must attribute OpenStax.

Attribution information
• If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:
Access for free at https://openstax.org/books/college-physics-ap-courses/pages/1-connection-for-ap-r-courses
• If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:
Access for free at https://openstax.org/books/college-physics-ap-courses/pages/1-connection-for-ap-r-courses
Citation information

© Jan 15, 2020 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License 4.0 license. The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.