Period 4: Transfer of Thermal Energy

Transcription

1 Name Section Period 4: Transfer of Thermal Energy 4.1 How Does Temperature Differ from Thermal Energy? a) Temperature Your instructor will demonstrate molecular motion at different temperatures. 1) What happens to molecular motion at higher temperatures? 2) Define temperature in terms of molecular motion. b) Thermal Energy 1) What is thermal energy? How does thermal energy differ from temperature? 2) Which has more thermal energy a cup of hot coffee or a bathtub full of warm water? 4.2 How Is Thermal Energy Transferred? a) Transferring Thermal Energy What is the one essential condition for the spontaneous transfer of thermal energy between two objects? b) Conduction 1) Before watching the demonstration, predict the order in which the steel balls will fall off of a metal rod when it is heated. Prediction: Answer: 2) What are the necessary conditions for heat transfer via conduction between two objects? 1

2 c) Thermal Conductivity Your instructor will discuss thermal conductivity. 12/22/12 1) You will heat a bar with four metal strips by placing it into a beaker of hot water provided by your instructor. BEFORE putting the strips into the water, predict the order (1 st, 2 nd, 3 rd, or 4 th ) in which the different metals will conduct heat from the water to change the color of the liquid crystal thermometer at the top of the strips. Prediction: Answer: Steel Aluminum Copper Brass 2) Before watching the next demonstration, predict the order in which the steel balls will fall off of rods made of different metals. Prediction: Answer: Why do the steel balls fall off in this order? 3) Touch the glass, metal, and cork squares. a) Do the squares feel as if they are all at the same temperature? b) Measure the temperature of the squares with an infrared thermometer. How do their temperatures compare? c) Why do the squares feel as if they are at different temperatures? 2

3 4) Your instructor will place ice cubes on two black squares on your table. What happens? Why? d) Convection Watch the demonstrations of thermal energy transfer via convection. 1) What are the necessary conditions for thermal energy transfer via convection? 2) Does convection involve a transfer of matter? 3) Does conduction involve a transfer of matter? e) Radiation Place the flood light an equal distance from the two cans fitted with balloons. 1) Which balloon inflates first? Why? 2) Why is the inside of a thermos silver-colored? 3) Does thermal energy transfer via radiation involve a transfer of matter? 4) Does thermal energy transfer via radiation require objects to be touching? 3

4 f) Examples of thermal energy transfer Place a small paper cup of water on the screen of the metal stand. Light the burner with a match and carefully move the burner under the paper cup. 1) Does the paper cup catch on fire? 2) Use an infrared thermometer to measure the temperature of the boiling water. (Point the thermometer at the water in the cup.) 3) Why didn t the cup catch on fire? 4) What forms of energy transfer are involved in heating the water? 5) Group Discussion Question: What do you think would happen if the paper cup were full of pennies instead of water? 4

5 Name Section Period 4 Exercises: Transfer of Thermal Energy 1. Explain the difference between temperature and thermal energy. 2. Suppose you are near a lit incandescent light bulb that is hot. What would be the primary form of thermal energy transfer from the bulb to your hand in each of the following cases? a) Your hand touches the bulb. b) You place your hand beside, but not touching, the bulb. c) You place your hand above the light bulb. 3. In class you touched pieces of glass, aluminum, and cork. a) Which material felt warmest? b) Which material felt coolest? c) Explain why you felt temperature differences for these materials. 4. In class you boiled water in a small paper cup over a burner. The paper cup may have turned brown on its bottom, but the cup did not catch on fire. Explain why the cup did not burn. 5