Temperature

Temperature (sometimes called thermodynamic temperature) is a measure of the average kinetic energy of a systems particles. Temperature is the degree of "hotness" ( or "coldness"), a measure of the heat intensity.
When two objects of different temperatures are in contact, the warmer object becomes colder while the colder object becomes warmer. It means that heat flows from the warmer object to the colder one.

Degree Celsius (^oC) and Degree Fahrenheit (^oF)

A thermometer can help us determine how cold or how hot a substance is. Temperatures in science (and in most of the world) are measured and reported in degrees Celsius (^oC). In the U.S., it is common to report temperature in degrees Fahrenheit (^oF). On both the Celsius and Fahrenheit scales the temperature at which ice melts (water freezes) and the temperature at which water boils, are used as reference points.

• On the Celsius scale, the freezing point of water is defined as 0 ^oC, and the boiling point of water is defined as 100 ^oC.
• On the Fahrenheit scale, the water freezes at 32 ^oF and the water boils at 212 ^oF.

On the Celsius scale there are 100 degrees between freezing point and boiling point of water, compared to 180 degrees on the Fahrenheit scale. This means that 1 ^oC = 1.8 ^oF.
Thus the following formulas can be used to convert temperature between the two scales:

t_F = 1.8 t_C + 32 = 9/5 t_C + 32         (1)
t_C = 0.56 (t_F - 32) = 5/9 (t_F - 32)         (2)
where
t_C = temperature (^oC)
t_F = temperature (^oF)

 celsius -fahrenheit diagram

 Degree Celsius and degree Fahrenheit are compared in the table below: 

Temperature
oC	oF
-20	-4
-15	5
-10	14
-5	23
0	32
5	41
10	50
15	59
20	68
25	77
30	86
35	95
40	104
45	113
50	122

Example - A patient with SARS (Severe Acute Respiratory Syndrome) has a temperature of 106 ^oF. What does this read on a Celsius thermometer?

t_C = 5/9 (106 - 32) = 41.1 ^oC

Kelvin - K

Another scale (common in science) is Kelvin, or the Absolute Temperature Scale. On the Kelvin scale the coldest temperature possible, -273 ^oC, has a value of 0 Kelvin (0 K) and is called the absolute zero. Units on the Kelvin scale are called Kelvins (K) and no degree symbol is used.
Because there are no lower temperatures than 0 K  - the Kelvin scale does not have negative numbers.
A Kelvin equal in size to a Celsius unit:

1 K = 1 ^oC

To calculate a Kelvin temperature, add 273 to the Celsius temperature:

t_K = t_C + 273.16         (3)

Example - What is the normal body temperature of 37 ^oC in the Kelvin scale?

t_K = t_C + 273.16 = 37 + 273.16
    = 310.16 K

Degree Rankine - R

In the English system the absolute temperature is in degrees Rankine (R), not in Fahrenheit:

t_R = t_F + 459.67         (4)