Summary
- Internal Energy
- The energy due to the coordinated motion (kinetic energy) and average position (potential energy) of a large collection of particles is usually known as mechanical energy, but is sometimes called external energy.
- The sum of the energies due to the random motion (kinetic energy) and local position (potential energy) of a large collection of particles is known as its internal energy.
- The symbol for internal energy is U.
- The SI unit for internal energy is the joule [J]
- Heat
- Two regions that can exchange internal energy are said to be in thermal contact.
- The net transfer of internal energy between two regions in thermal equilibrium is zero.
- Heat is the net transfer of internal energy from one region to another.
- The symbol for heat is Q (probably from "quantity of heat").
- The SI unit for heat is the joule [J]
- Temperature
- Temperature can be defined informally as the measure of a region's "hotness".
- A region which is "hot" has a higher temperature than one that is "cold".
- Two regions have the same temperature when there is no net exchange of internal energy between them.
- Heat flows from one region to another due to a difference in temperature. (Heat flows from "hot" to "cold".)
- No heat flows between two regions with the same temperature.
- The symbol for temperature is T.
- A device that can be used to measure temperature is called a thermometer.
- All thermometers measure the value of some thermometric variable that responds to changes in temperature.
- Thermometers can be classified according to the thermometric variable measured.
- A temperature scale is built from…
- at least two fixed points (an upper fixed point and a lower fixed point) corresponding to the temperatures of a pair of reproducible experiments and…
- a fundamental interval or span of numbers between the two fixed points
- The SI unit of temperature is the kelvin [K].
- Symbology
- In current usage, the kelvin is always written in lowercase letters without a degree symbol [K].
- In some early 20th century sources it was common to see degree Kelvin [°K], but this is no longer considered acceptable.
- The kelvin is is one of the seven base units of the International System of Units.
- The kelvin is now defined by relating the defined value of Boltzmann's constant (k = 1.380649 × 10−23 J/K) to the definitions of the meter, kilogram, and second.
- The original definition of the kelvin temperature scale is still approximately true with…
- the triple point of water as the upper fixed point
- absolute zero as the lower fixed point
- 273.16 K as the fundamental interval
- The degree Celsius [°C] is an acceptable non SI unit for temperature.
- Symbology
- The reversed phrase Celsius degree [C°] is sometimes used for temperature intervals (ΔT).
- The original name for this unit was the degree centigrade [°C], but this is no longer considered acceptable.
- The degree Celsius and kelvin have the same size, but assign zero to different values.
- Absolute zero is assigned the exact value −273.15 °C.
- The original definition of the Celsius temperature scale is still approximately true with…
- the normal boiling point of water as the upper fixed point
- the normal freezing point of water as the lower fixed point
- 100 °C as the fundamental interval
∆T |
[K] |
= |
∆T |
[°C] |
|
T |
[K] |
= |
T |
[°C] |
+ 273.15 |
T |
[°C] |
= |
T |
[K] |
− 273.15 |