1. Heat Transfer! CH22 Physics (B) Winter, 2010-2011

2. What is Heat Transfer? Heat Transfer: The flow of heat energy from a hot body to a cold body To answer that, let’s think about how you can get to school? (three ways or “modes”) – Walk/Ride Bike – Drive – Bus Heat Energy is like you, and can travel in three ways or “modes” – Conduction – Convection – Radiation 2

3. Heat Transfer: Conduction Conduction: The mode to transfer heat energy where two objects are in direct contact with each other Common in solids Requires presence of matter Must have DIRECT CONTACT 3

4. Heat Transfer: Conduction Solid Metals are good conductors: materials that flow heat energy well Plastics/Rubber are good insulators: materials that DO NOT flow heat energy well EXAMPLE: Do your feet feel colder on tile than on carpet? Why? EXAMPLE: If you hold one end of a metal rod against ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand? 4

5. Heat Transfer: Convection Convection: The mode to transfer heat energy where there is CIRCULAR movement of fluids caused by their different densities at different temperatures Predominant in liquids & gases, and matter must be present, like conduction Can be forced or free convection: forced involves a fan/motor to move air/liquid 5

6. Heat Transfer: Convection Convection is present throughout your world: Earth’s atmosphere/weather: winds, ocean temps, ocean currents Earth’s core: convection currents driving Plate Tectonics In your home? Let’s make a list! 6

7. Heat Transfer: Radiation Radiation: The mode to transfer heat energy where electromagnetic waves carry the heat energy via light Matter is not required Solar energy utilizes radiation: Sun’s Light rays flow heat from sun to whatever object is in contact with the light rays Can see it in Fire, or radiators in old homes… 7

8. Heat Transfer Let’s Go Transfer Some Heat! 8