Temperature is directly related to the average speed of the random motion of the atoms in a substance. 

Faster atoms = hotter substance

 

Temperature is actually a measure of the average kinetic energy of the atoms in a substance.

Kinetic energy is proportional to speed, but it is not the same thing:  K.E. = ˝ mv2

 

There is no limit to the amount of  kinetic energy an can have, so there is no absolute highest possible

temperature.  However, there is an absolute minimum energy an atom can have — zero.  Therefore, there is

a limit to how cold atoms can get, and we call this absolute zero.

 

Absolute zero is the temperature at which atoms have no more kinetic energy of random movement.

 

There are three commonly used temperature scales:  Fahrenheit, Celsius, and Kelvin

 

Fahrenheit was a doctor, so he placed 100o at normal body temperature (I know what you’re thinking, and no, 98.6o is not normal body temperature), and 0o at the coldest thing he could find, a mix of salt and snow

 

(read about the myth of 98.6 oF here:  link )

 

 

Celsius set 100o at the temperature of boiling water and 0o at the temperature of freezing water

 

 You do not have to learn to convert between oF and oC, but please learn the following for estimating 

                                                100 oC = boiling water

                                                 40 oC  = heat wave temperatures

                                                 37 oC  = normal human body temp

                                                 20 oC  = room temp

                                                   0 oC  = freezing water/ melting ice

                                                -273 oC  =  absolute zero

 

Absolute zero can be thought of as the temperature at which the atoms stop moving (actually it is the temperature at which atoms can no longer lose any more kinetic energy, or energy of motion)

 

Kelvin realized that a temperature scale should put zero at absolute zero, so he took the Celsius scale and shifted zero down 273o so that zero Kelvins was absolute zero.

 

To convert from Kelvins to Celsius  subtract 273  (ex:  194K – 273 = -79) 

Remember, Celsius can have negative numbers, so subtract 273.

To convert from Celsius to Kelvins add 273          (ex:   194oC + 273 = 467)

Remember, Kelvins can not have negative numbers, so add 273

 

 

(Read more about the three temperature scales here:  link)

 

The Kelvin scale is the best because it is a direct measure of atomic motion, if you double the temperature, you double the kinetic energy of the atoms.  This is not true for either Celsius or Fahrenheit.

 

Since temperature is a measure of the average kinetic energy of the atomic motion of a substance, and

K.E. = ˝ mv2  doubling the temperature is not the same thing as doubling the speed of the atoms.  If you double the speed of the atoms, you quadruple the temperature in Kelvins (v2 )

 

Example: water boils at 100o C.  What would the temperature of the water be (in o C) if the average kinetic energy of the atoms was doubled?

First, convert to Kelvins: 100o C + 273 K = 373 K, then double the value 373 ´ 2 = 746 K, then convert back to Celsius 746 K - 273 = 473 oC