Physics Notes - Chapter 22
Heat Transfer
- Chapter 22 Terms and Objectives
- Three Methods to Move Energy (Three Types of Thermal Contact)
- Conduction
- conductor - a material that transmits energy readily
- example:
- metals, where "free" valence electrons carry energy from place to place
- insulator - a material that does not transmit energy readily
- transfers energy through atom to atom interaction
- transfer of energy is slow
- Works best in solids. Liquids and gasses are generally poor conductors of heat.
- Simulation: Passing a note from student to student.
- Convection
- give energy to atoms/molecules, then move the energetic atoms/molecules
- won't work in solids, since molecules are locked in place
- although conduction in metals is often considered convection in an "electron cloud"
- best in fluids
- a very efficient way of moving energy in liquids and gasses
- Simulation: A student gets out of her/his seat and walks over and delivers the note to its recipient
- Radiation
- energy transmitted by electromagnetic waves
- the electromagnetic spectrum
- infrared & visible
- transmits heat energy without using matter to carry the energy
- good absorbers are good emitters
- very efficient way to move energy
- Simulation: The first student tosses the note to its recipient
- Newton's Law of Cooling
- rate of cooling (rate of energy transfer) is proportional to the temperature difference
- large temperature difference means energy moves quickly
- small temperature difference means energy moves slowly
- Demo: Rate of cooling
last update January 28, 2006 by JL Stanbrough