Chapter 9-2: Defining Heat

1. Chapter 9-2: Defining Heat St. Augustine Preparatory School January 11, 2017

2. What is heat?

3. Heat • Heat is the energythat is transferred from one object to another because of a temperature difference. • Heat moves from areas of high concentration to areas of low concentration (hot to cold objects). • Radiation • Conduction • Convection

4. Heat Transfer – Three Methods • Radiation: Heat travels in the form of electromagnetic waves from a warmer object to a cooler object. No physical contact is required. • Conduction: Occurs between objects in contact when a temperature difference is present. The temperature difference means that the molecules in the two objects have different kinetic energies. The collisions between the two objects result in an energy transfer. • Convection: occurs when warmer areas of a liquid or gas rise to cooler areas in the liquid or gas. As this happens, cooler liquid or gas takes the place of the warmer areas which have risen higher. This cycle results in a continuous circulation pattern and heat is transferred to cooler areas

5. Radiation from the Sun to the Earth. The Sun is emitting heat in a form of electromagnetic radiation (infrared waves). Conduction from box A to box B through physical contact. Convection in the water, conductionbetween the tea pot and the burner. https://www.youtube.com/watch?v=yUEPGMnRqGs

6. Radiation • Thermal imaging is possible as a result of different objects radiating different amounts heat. • Note: “Night vision” is very different from thermal imaging as it detects small amounts of light, rather than heat.

7. What are some possible uses for thermal imaging?

8. Uses for Thermal Imaging • Police and Military: https://www.youtube.com/watch?v=YwAfIDX4xYs • Firefighters • Life in Thermal: https://www.youtube.com/watch?v=iRmgnWzi0DE • Doctors: https://www.youtube.com/watch?v=WwKEMp8hIn4 • Dentists

9. Conduction – result of molecular collisions

10. Heat Transfer • The greater the difference of the temperature between two objects, the greater the rate of energy transfer between them is.

11. Thermal Conduction • If a cardboard food container and a metal tray are removed from the freezer, which feels colder? Are they at different temperatures?

12. Thermal Conduction • Objects that rapidly transfer energy as heat are called thermal conductors. (metals) • Objects that slowly transfer energy as heat are called thermal insulators (plastic, wood, etc.)

13. Questions to be completed • How come blowing on your hands when they are cold will heat them up, yet blowing on a bowl of soup will cool it down? Use a microscopic interpretation for your answer (what are the molecules doing?) • A bottle of water at room temperature is placed in a freezer for a short time. An identical bottle of water that has been lying in the sunlight is placed in a refrigerator for the same amount of time. What must you know to determine which situation involves more energy transfer. • A friend tells you that fluffing up a down sleeping bag before you go to bed will keep you warmer than sleeping in the same sleeping bag when it is still crushed from being in it’s storage sack. Explain why this happens. • What are three methods of heat transfer? Provide a real world example for each method that was not given in the slides.