Heat and Heat Transfers

1. Heat and Heat Transfers

2. What is heat? • Heat is a tricky word and can mean different things depending how you look at the definition. • For our purposes heat is the amount of thermal energy an object has based on the motion of the molecules in the object. • Fast Molecules = Hot • Slow Molecules = Cold

3. How does heat move? • Heat (thermal energy) always transfers from high concentrations to low concentrations. • Heat moves from hot to cold.

4. In what way does heat move? • Conduction: Heat moves from hot to cold by DIRECT CONTACT. • Example: Warming your hands by holding a nice warm mug of hot chocolate. • Example: Cooking pancakes on the griddle.

5. In what way does heat move? • Convection: Heat moves from hot to cold by CURRENTS IN A FLUID. • Example: Warming your hands by blowing your warm breath on them. • Example: Cooking fruit with steam.

6. In what way does heat move? • Radiation: Heat moves from hot to cold by ELECTROMAGNETIC WAVES (mainly infrared and light). • Example: Warming your hands by holding them near the fire. • Example: Toasting marshmallows over a fire. • Example: Baking a pie with an Easy-Bake Oven.

7. Let’s apply this to weather now.

8. Where does the Earth receive most of its heat from? • The Sun How does the energy from the Sun get to the Earth? Radiation • Radiation

9. What are the two main types of Earth’s surfaces? • Landmasses • Bodies of Water Bodies of Water Landmasses How does the Sun’s energy affect the heating of the different surfaces of the Earth ?

10. Specific Heat Capacity: • Specific heat capacity is the ability of an object to absorb and hold heat. • High Specific Heat: The object heats and cools slowly. The object DOES hold its heat well. (Example: Cast Iron Skillet) • Low Specific Heat: The object heats and cools quickly. The object DOES NOT hold its heat well. (Example: Asbestos)

11. How does the Sun’s energy affect the heating of the different surfaces of the Earth ? • Landmasses (Soil Beaker) : Soil has a lower specific heat capacity so the temperature of the soil heats up more quickly but then loses its heat quickly too. • This is partially due to the fact that the Sun’s (lamp’s) energy is trapped in the upper levels of the soil and does not penetrate to the bottom of the soil.

12. How does the Sun’s energy affect the heating of the different surfaces of the Earth ? • Large Bodies of Water (Water Beaker) : Water has a higher specific heat capacity so the temperature of the water heats up more slowly but then keeps its heat better than the soil. • This is partially due to the fact that the Sun’s (lamp’s) energy can move to all parts of the water (even the deep parts) and spread out.

13. When the soil loses its heat, where does the heat go? • The heat is transferred to the air surrounding the soil. What type of heat transfer is this an example of? • Radiation

14. Another example of heat loss by radiation: Tree Wells are created when the tree absorbs the energy from the sun and then loses the heat (via radiation) and melts the snow around the trunk. Tree Wells can be fatal to skiers, snowboarders and other winter recreationalists.

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