Name: Hr: Activity 3.3.6 Heat Transfer Introduction Heat is the transfer of thermal energy. Thermal energy exists when the atoms or molecules in a substance are in motion and vibrate. The atoms possess kinetic energy, which creates thermal energy. The amount of thermal energy an object has is the sum of the kinetic energy of all of the particles. That s why a bathtub of water has more thermal energy than a sink of water when the water is the same temperature in both. If thermal energy is lost, these vibrations slow down. If thermal energy is gained, these vibrations increase. If enough thermal energy is added to a substance, the vibrations may even cause a solid material to lose its form and melt, or a liquid substance to evaporate, or a gaseous substance to expand as the distance between particles increases. Thermal energy can be transferred from one place to another when a temperature difference exists. Heat transfer always occurs from the direction of the higher temperature to the cooler temperature. Heat transfer in a bathtub occurs from the hot water to the cooler air, floor, tub sides, and person in the water. Temperature is a measure of the average kinetic energy that the particles in a substance have at a particular location. Many scales are used to measure temperature, such as Fahrenheit, Celsius, and Kelvin. A cup of boiling water may have a higher temperature than a bathtub of warm water because the average kinetic energy of the particles is higher. However, if you were to sum up the kinetic energy of all of the water molecules in the tub, it would have a higher total thermal energy. Temperature is like counting the money one person in a room has in their pocket. Thermal energy is like counting the money that everyone in the room has and adding it all up. Heat transfer occurs when thermal energy is transferred. In this activity you will watch several demonstrations performed by your teacher. You will summarize what you learn about heat transfer in the conclusion questions below. Equipment PLTW Gateway notebook Pencil 6 Digital thermometers 6 soda cans, 1 wrapped with aluminum foil, 1 with paper towel, 1 with plastic wrap, 1 with wool sock, 1 with cotton sock Stainless steel tray and plastic tray Stainless steel spoon and plastic spoon (one set per group) Cardboard house with roof painted black Mylar blanket Shop light with 150 watt light bulb Stand for clamping shop light Fish tank LCD thermometers PLTW Gateway Energy and the Environment Activity 3.3.6 Heat Transfer Page 1
Procedure Watch as your teacher completes several demonstrations. The information you will learn from these demonstrations will help you engineer a product during a future project. Conduction and Insulation Demonstrations Soda Can Wrap 1. Complete the chart below. First number your predictions 1 through 6, with #1 being the wrap that keeps the soda coldest. Record the temperature of each can and a reading from earlier or later in the day that your teacher provides. How did your prediction compare to the actual temperature? Material Wool sock Paper towel Aluminum Plastic wrap Cotton sock Nothing Your Prediction Temperature at Time 1, F Temperature at Time 2, F 2. Complete the bar graph below to show the temperatures at Time 1 and Time 2 for each. PLTW Gateway Energy and the Environment Activity 3.3.6 Heat Transfer Page 2
3. Draw a picture of how you think the cans get warm over time. If you use arrows, be sure to label them. Metal Spoon vs. Plastic Spoon 4. Which spoon made the ice melt faster? Why? 5. We discussed conduction and insulation;; describe the difference between a conductor and an insulator. 6. Which spoon is a conductor? Which spoon is an insulator? Metal Tray vs. Plastic Tray 7. What is the temperature of the plastic tray? 8. What is the temperature of the metal tray? 9. Why does the metal tray feel colder? 10. Draw how heat is being transferred when you touch the metal tray. PLTW Gateway Energy and the Environment Activity 3.3.6 Heat Transfer Page 3
11. Draw how heat is being transferred when you hold the metal spoon. Convection and Radiation Demonstrations 12. Describe the difference between convection and radiation. 13. Sketch a picture of a house and describe how and where convection and radiation occur in and around a house. 14. Draw a picture with arrows showing how heat was transferred when the house was flipped upside down, and label your arrows. Conclusion 1. Why does one type of sock prevent heat transfer better than another? 2. Why does one type of food wrap prevent heat transfer better than another? 3. Which material was the best insulator? 4. Why are some fabrics better to wear in the winter than others? PLTW Gateway Energy and the Environment Activity 3.3.6 Heat Transfer Page 4
5. Would a penguin-shaped ice cube last longer sitting on a metal surface or a plastic surface? 6. Record the appropriate type of heat transfer (conduction, convection or radiation) in the box with each example. The sun makes you feel warm. Meat is heated in a frying pan. The primary method of heat transfer in a fluid. Smoke and hot air travel up a chimney. The handle of a saucepan gets hot when it is on the stove. You keep your window open for ventilation. A pinwheel over a candle starts to spin as a result of air movement. The outside of a bowl of soup becomes hot. A tin cup gets hot when you pour coffee into it. The roof of your car gets hot in the sun. On a bright, sunny day, the pavement becomes very hot. Transfer of heat by direct contact. It produces winds. You cook a hotdog over a campfire. Water moves in a saucepan when it is heated. The outside of a pipe gets hot when it carries hot water. Your body is warmed by a sun lamp. Heat is transferred in water by currents. You become warm standing in front of a fireplace. The second floor of a house is usually hotter than the first floor. Material used under license from Christine G. Schnittka, Ph.D. in cooperation with Virginia Middle School Engineering Education Initiative. PLTW Gateway Energy and the Environment Activity 3.3.6 Heat Transfer Page 5