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Conduction & Convection Class Exercises AP Physics 1. How can heat occur between two objects? What forms of energy are exchanged between two objects? 2. How does conduction happen? 3. In the collisions between the molecules that make up two different objects that are in contact with each other, does the energy always get transferred from the hot object to the cool object? *Newton’s Law of Cooling Activity 4. What does Newton’s Law of Cooling say? 5. Why is it more expensive to keep your house heated to 80 °F than at 65 °F during the winter? 6. What factors affect the amount of heat that occurs to an object? What else could you change that will affect the amount of energy that an object loses or gains? 7. You go into the kitchen to fry a meal and find that you have a choice of two aluminum frying pans: one with a thin bottom and the other with a thick bottom. Assuming that you will use them with the burner on the same setting, which one will let you cook your food more quickly? Explain. 8. Bleacher seats are commonly made from either wood or aluminum. Both types of seats are at the same temperature as the air around them, but the aluminum seats will feel colder than the wood seats. Why is this? 9. Why is it more expensive to heat a larger house? 10. Why do people who live in really cold climates wear big bulky coats? 11. If you put your hand in a hot oven, it is uncomfortable but bearable, yet if you grab a glass baking dish that is at the same temperature as the oven, you get burned. Why? 12. What is the purpose of the fins on the radiator of a motorcycle engine or automobile engine? 13. What is the equation that expresses how quickly energy is transferred through an object? 14. You are frying a 10 cm by 10 cm block of something yummy in a 1 cm thick cast iron frying pan. a) If the burner beneath the stove is at 800 °C and the yummy stuff is at 4 °C, how much energy goes into the food every second? b) Once the food is heated up to 80 °C, how much energy is transferred into the food every second? 15. Assume you have a two story house with 6 m tall walls and a base floor that is 8 m side by 10 m deep. You want to keep the temperature inside the house at 20 °C while it is 5 °C outside. a) How much heat would you lose through the walls every second if the walls were made out of 2 cm thick wood? b) How much heat would you lose through the walls every second if the walls were made out of 10 cm thick brick? 16. Suppose you add a layer of 9 cm thick fiberglass insulation, to the walls of your house (from problem 15), then how much heat will you lose through your walls every second? 17. A fancy pot has two layers of metal on the 20 cm diameter bottom – a 3 mm layer of copper and a 2 mm layer of stainless steel. If you place it over a 1200 °C flame, how much energy will it transfer every second to your food which is at 95 °C? 18. Your body is insulated by your clothing and by the layer of air that it holds next to your body. Assume that your body has 1.5 m2 of surface area and a skin temperature of 25 °C. If you wear a 1 cm thick cotton snowsuit, which sits 2 cm off your skin on a day when the outside temperature is –15 °C, how much energy will your body lose every second? 19. Why do you feel colder on a windy day than on a day when the air is still? 20. What is convection? When does it happen? How does it affect the transfer of energy between object? 21. What is the point of adding fiberglass insulation in the walls of your home? How does that reduce the energy transfer through the walls? *22. Why do radiators heat up a whole house instead of just the air around them?
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