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Internal Energy. Liceo Da Procida. Lesson 3. Review. Last time: Heat propagation Conduction (two things touching, thermal conductivity) Convection (fluids flowing) Radiation (two things not touching, electromagnetic waves) Today: Effects of heat propagation inside a material.
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Internal Energy • Liceo Da Procida Lesson 3
Review • Last time: Heat propagation • Conduction (two things touching, thermal conductivity) • Convection (fluids flowing) • Radiation (two things not touching, electromagnetic waves) • Today: Effects of heat propagation inside a material
Reminder Question What is thermal conductivity? • A quantity measured in degrees Celsius • How much energy it takes to increase the temperature of a material • Energy transfer due to a temperature difference • A measure of how well a material conducts heat
Reminder Question What is thermal conductivity? • A quantity measured in degrees Celsius • How much energy it takes to increase the temperature of a material • Energy transfer due to a temperature difference • A measure of how well a material conducts heat
Heating Different Materials During the summer time, when you walk from the sand into the ocean, which is hotter? Why could this be?
Sand vs. Water • The sun transfers heat to the sand and water • What kind of heat propagation is this? • The sand and water each get the same amount of heat from the sun • Why does one get hotter than the other? vs.
Heat Capacity • The sand and water are at different temperatures because they have different heat capacities • Heat capacity tells us how quickly a material’s temperature will increase for a given amount of heat transfer • Think of a pie: the crust and filling get the same amount of heat from the oven, but which part do you burn your mouth on?
Heat Capacity vs. Thermal Conductivity • Thermal conductivity = how well a material will conduct heat (heat passing, heat transfer) • Heat capacity = how quickly something will heat up (heat staying, temperature) • Heat going through the walls vs. temperature of the walls vs.
Heat Capacity vs. Thermal Conductivity Practice Are each of these examples of heat capacity (1) or thermal conductivity (2)? • I make a pizza and the tomato sauce gets hotter than the cheese • I burn my mouth when I eat the pizza • A pot doesn’t feel hot if I use a glove to hold it • Gold increases its temperature more quickly than silver • Walking barefoot across the street feels hotter than walking on the sidewalk
Specific Heat Capacity If we look at the heat capacity per mass, we call this specific heat capacity. A high specific heat capacity means that something takes a long time to heat up, while a low specific heat capacity means something heats up quickly. Water has an extremely high specific heat capacity, while metals do not.
Calculating Specific Heat Capacity • We have a formula that relates: • heat (Q) • mass (m) • specific heat capacity (c) • change in temperature (ΔT) • Q = m c ΔT
Concept Question Remember, Q = m c ΔT If I increase the specific heat capacity, will it take more or less heat to increase the temperature by 1 degree? • More heat • Less heat
Concept Question Remember, Q = m c ΔT If I increase the specific heat capacity, will it take more or less heat to increase the temperature by 1 degree? • More heat • Less heat
Concept Question Remember, Q = m c ΔT Remember the beach question. Does sand or water have a higher specific heat capacity? • Sand • Water
Concept Question Remember, Q = m c ΔT Remember the beach question. Does sand or water have a higher specific heat capacity? • Sand • Water
Video Specific heat capacity/global warming
Specific Heat Capacity of Water The specific heat capacity of a material is usually not a constant - it changes with temperature. However, we generally only work around 15 deg. C, so we take the specific heat capacity of water as 1 C/g, or 4.184 J/g.
Internal Energy • Remember, heat is a kind of ENERGY • When you add heat energy to an object, where does that energy go? • The energy is used to increase the temperature, and it is stored in the object • Since it is stored in the object, we refer to this energy as internal energy • Change in internal energy = heat added to the object • ΔU = Q
Practice Problems Remember, Q = m c ΔT • How much heat is absorbed when 500. g of water , c = 4.184 J/goC, goes from 25.0oC to 35.0oC? • What is the change in internal energy when 500. g of copper, c = 0.385 J/goC , goes from 25.0oC to 35.0oC? • I have a cup filled with 0.150kg of coffee (c=4187J/kg°C) at 70°C. I add 0.01kg of milk (c=3800J/(kg°C)) at 5.0°C. What is the final temperature of the coffee and milk mixture? • I made a bowl of minestrone soup (c=4187J/kg°C). I then put 0.6kg of soup at 90°C in a 0.2kg glass bowl (c=840J/kg°C) that is initially at 20°C, what will be the temperature of the soup and the bowl when they have reached equilibrium?