Chapter 12.1

Temperature and Thermal Energy

What makes a hot body hot?

• In the 18th century scientists came up with the caloric theory of heat

• In this theory an invisible substance called “caloric” created heat.

• Only in the mid-nineteenth century did scientists develop the kinetic-molecular theory.

• This stated that as the particles moved faster they created a greater kinetic energy and thus heat.

Thermal Energy and Temperature

• According to the kinetic-molecular theory hot bodies have a greater average thermal energy than a cold body.

• Temperature is measured on a definite scale. • Thermal energy is

proportional to the

number of particles in

the object,

while temperature

is not.

Equilibrium and Thermometry

• Temperature is measured using a process called conduction.

• When your body and the thermometer are at the same temperature they are at thermal equilibrium.

• Thermometers contain a liquid that will expand when heated and retract when cooled, thus the liquid rises and falls.

Temperature Scales: Celsius and Kelvin

• Each interval on the kelvin scale is called a kelvin.

• A reading of 0oC is where water freezes.

• However, a reading of 0K is absolute zero.

• At absolute zero all molecules cease to move.

• We have never been able to create conditions of absolute zero.

Heat and Thermal Energy

• Heat is the energy that flows between two objects due to a temperature difference.

• The transfer of energy through electro-magnetic waves is radiation.

• The motion of fluid due to a temperature difference is called convection.

• The specific heat of a material is the amount of energy needed to change its temperature

Specific Heat of Common Substances

Material Specific heat Material Specific heat

J/kg x K J/kg x K

aluminum 903 lead 130

brass 376 methanol 2450

carbon 710 silver 235

copper 385 steam 2020

glass 664 water 4180

ice 2060 zinc 388

iron 450

Heat Transfer

• Q=mCT = mC(Tfinal – T initial)

• T= temperature (K)

• m= mass (Kg)

• Q= heat gained or lost (J)

• C=specific heat (J/Kg*K)

heat transfer. Chart. Heart Transfer. N.p., n.d. Web. 11 Jan. 2011. <http://www.aos.wisc.edu/ ~aalopez/aos101/wk5.html>.

heat transfer. Chart. Heart Transfer. N.p., n.d. Web. 11 Jan. 2011. <http://www.aos.wisc.edu/ ~aalopez/aos101/wk5.html>.