Ice Melting Cubes Block A Feels Cold Block B Feels Warm Aluminum Conducts heat very well

Heat Transfer Heat always transfers from hot objects to cold objects. Metals conduct heat very well partially because valence electrons are delocalized and can flow freely and transfer energy. Heat always transfers from hot objects to cold objects. Metals conduct heat very well partially because valence electrons are delocalized and can flow freely and transfer energy.

Heat vs Temperature Temperature is the average energy of the molecules in a substance. Heat is the transfer of that energy between objects Question: A sparkler can get up to 3000°F, why doesn’t it burn you? Answer: Heat transfer is dependent upon mass!

Heat transfer by Radiation Heat transfer by convection Heat transfer by conduction Heat from a closed system to surroundings Q = heat transferred in joules (J) m = mass of material in grams (g) c =specific heat of material (J/g°C) ΔT = change in temperature k = thermal conductivity of material A = cross sectional area t = times in seconds d = thickness of material H c = heat transfer coefficient σ =Stefan Boltzmann Constant Q = heat transferred in joules (J) m = mass of material in grams (g) c =specific heat of material (J/g°C) ΔT = change in temperature k = thermal conductivity of material A = cross sectional area t = times in seconds d = thickness of material H c = heat transfer coefficient σ =Stefan Boltzmann Constant

Calculate the Heat lost by the block when iron block decreases its temperature from 60 o C to 40 o C if the mass of the body is 2 Kg. Specific heat of iron C = 0.45 kJ/kg C. Qlost = mcdt A room is maintained at 20 o C where as temperature outside the room is 10 o C. There is one of the window in the corner having area 1m by 2m. Calculate the heat transfer? Thermal Conductivity of glass is 1.4 W/mK. How much energy does it take to raise the temperature of 50 g of copper by 10 0C? Copper has a specific heat of J/gC Q =mcdt If we add 30 J of heat to 10 g of aluminum, by how much will its temperature increase? Q =MCDt

Heat is transferred between objects (hot to cold) until they are all the same temperature. If we had two objects next to one another, one hot and one cold, what would happen over time? 90°C10°C 50°C Thermal equilibrium: objects are the same temperature and no more heat will be transferred.

Conduction, Convection and Radiation Image Src

Convection: heat transfered through a moving fluid (e.g. air or water). Hotter fluids rise up and colder fluids sink. Ex. Boiling water, hot air rising, hot air balloons, plate tectonics. Conduction: heat transfer through touching via molecular collisions. Ex. Touching a hot cup of coffee, a metal pan getting hot on a burner, stepping on hot sand. Radiation: transfer of thermal energy through space via electromagnetic radiation without the need of conduction or convection. Space is empty and this is how the sun’s heat travels 93 million miles through a vacuum to reach us. hyperphysics Img src

Wind Chill Effect 1.Our bodies generates a natural shield of heat which surrounds us. 2.Air is a very poor conductor of heat so this layer keeps up warm. 3.When wind blows it removes this natural layer of heat allowing our body to cool more quickly. Warm Cold Heat Shield No Heat Shield WIND

1.Its 30°F outside and wind is 20mi/hr, what is the apparent temperature? 2.Why is it important to cover your skin when its cold and windy out? 3.It is forecasted to be 10°F outside with 20mi/hr wind what temperature would a car be?

In Norilsk, Russia, 'the coldest city on earth' it gets so cold (~- 50C) that the fuel freezes in the tanks, and has to be melted in the tanks