SG_Chap11 - 11/9/2009 Chapter 11 Energy in Thermal...

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11/9/2009 1 11.1 Heat and Internal Energy Heat and internal energy are different! Internal Energy , U, is the energy associated with the microscopic components of the system. (Kinetic energy and bond energy of molecules/atoms) Heat, Q , is the transfer of energy between a system and its environment because of a temperature difference between them. (Coffee cup) Chapter 11 Energy in Thermal Processes Energy flows from hot (high T) to cold (low T) Units of Heat Since heat is redistribution of internal energy, its unit is same as energy: Joules More commonly (mis)used:calorie 1 cal = 4.186 J In food labels, Calorie=1000 cal = 4186 J !! Example If a 70 kg person goes to the top of a 10 story building, say around 40 m high, how much work is done? W = mgh = 70 x 9.8 x 40 = 27440 Joules = 6.6 Calories A can of soda ~ 150 Calories Have to go up 909 m high to use up 150 Calories As a reference: Empire State Building is 448 m tall. One can of soda, two Empire State Buildings!
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11/9/2009 2 Thankfully, our body is not all that efficient! Muscles use up more calories than the work done. Releasing heat: major source of calorie loss Same person runs 1 km (much easier than going up 909 m). Experts say 75 Calories will be burned. 2 km for a can of coke ( A can of soda ~ 150 Calories) Not a very appealing deal, considering calories!!! But, it does make you healthy!!
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SG_Chap11 - 11/9/2009 Chapter 11 Energy in Thermal...

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