- Slides: 9
Thermal Energy 11/13/2012
What is thermal energy? • Thermal energy is also known as heat and is the kinetic energy of all the molecules in a material. • If molecules are moving fast… – (1) Do they have more or less kinetic energy? – (2) Does the material have more or less thermal energy? – (3) Do you predict it will be a high or low temperature?
Temperature • Temperature is a number related to the average kinetic energy of the molecules of a substance. • Heat, however, IS the energy in a substance and is measured in Joules, just like all the kinds of energy we have been talking about. http: //phet. colorado. edu/en/simulation/gas-properties What happens to the molecules in a gas when you add more energy or heat to the gas? Describe what you see in the simulation.
Heat • Heat is thermal energy that is transferred between two bodies due to a difference in temperature. If one object is higher temperature than the other, heat will flow from high to low temperature. • Heat transfer is the process of increasing the kinetic energy of a materials’ particles from a material of high temperature to one of lower temperature.
Three kinds of thermal energy transfer • Conduction • Convection • Radiation
Conduction • Conduction is the transfer of heat by direct contact (mostly with solid objects). • Molecules in one material can increase the energy of molecules in the other material. • Materials that allow heat to flow through them are called conductors (metals are good conductors). • Materials that do not conduct heat well, such as plastic and wood, are called insulators.
Convection • Convection is the transfer of heat by the movement of the medium itself and occurs in liquids and gases but not in solids. • Hot areas of the material flow and mix with cool areas (like in air conditioning). • Convection transfers heat over a distance faster than conduction but cannot transfer to solid objects.
Radiation • Radiation is the transfer of heat in the form of waves through space. • Hot objects give off infrared electromagnetic radiation, which can be absorbed in another object and heat it up. • Transfer of heat by radiation moves at the speed of light and can go great distances, for example from the Sun to the Earth.
Exit Slip (turn in!) • What is thermal energy? • If you add heat to air in a balloon by putting it over a candle, what kind of heat transfer are you using? • For that balloon, what do you think would happen to the air molecules inside?