tailieunhanh - Lecture Thermodynamics

In mechanics we deal with quantities such as mass, position, velocity, acceleration, energy, momentum, etc. Question: What happens to the energy of a ball when we drop it on the floor? Answer: It goes into heat energy. Question: What is heat energy? | Thermodynamics Temperature, Heat, Work Heat Engines Introduction In mechanics we deal with quantities such as mass, position, velocity, acceleration, energy, momentum, etc. Question: What happens to the energy of a ball when we drop it on the floor? Answer: It goes into heat energy. Question: What is heat energy? The answer is a bit longer. In Thermodynamics we deal with quantities which describe our system, usually (but not always) a gas. Volume, Temperature, Pressure, Heat Energy, Work. We all know about Volume. Pressure: Demonstrations: Balloons, Bed of Nails, Magdeburg hemispheres. Example 120 lb woman putting all her weight on 2in2 of heals. Pressure = 120 lb/2in2 = 60 lb/in2. Is that a lot? Comparison: 1 atm = lb/in2. Thus of heals is approximately 4 atm. This is the pressure you would feel at a depth of approximately 133 ft of water. Temperature and Heat Everyone has a qualitative understanding of temperature, but it is not very exact. Question: Why can you put your hand . | Thermodynamics Temperature, Heat, Work Heat Engines Introduction In mechanics we deal with quantities such as mass, position, velocity, acceleration, energy, momentum, etc. Question: What happens to the energy of a ball when we drop it on the floor? Answer: It goes into heat energy. Question: What is heat energy? The answer is a bit longer. In Thermodynamics we deal with quantities which describe our system, usually (but not always) a gas. Volume, Temperature, Pressure, Heat Energy, Work. We all know about Volume. Pressure: Demonstrations: Balloons, Bed of Nails, Magdeburg hemispheres. Example 120 lb woman putting all her weight on 2in2 of heals. Pressure = 120 lb/2in2 = 60 lb/in2. Is that a lot? Comparison: 1 atm = lb/in2. Thus of heals is approximately 4 atm. This is the pressure you would feel at a depth of approximately 133 ft of water. Temperature and Heat Everyone has a qualitative understanding of temperature, but it is not very exact. Question: Why can you put your hand in a 400 F oven and not get instantly burned, but if you touch the metal rack, you do? Answer: Even though the air and the rack are at the same temperature, they have very different energy contents. Construction of a Temperature Scale Choose fixed point temperatures that are easy to reconstruct in any lab, . freezing point of water, boiling point of water, or anything else you can think of. Fahrenheit: Original idea: 0 F Freezing point of Salt/ice 100 F Body Temperature Using this ice melts at 32 F and water boils at 212 F (Not overly convenient) Note: 180 F between boiling an freezing. Celsius (Centigrade) Scale: 0 C Ice Melts 100 C Water Boils Note a change of 1 C = a change of F. Conversion between Fahrenheit and Celsius Absolute or Kelvin Scale The lowest possible temperature on the Celsius Scale is -273 C. The Kelvin Scale just takes this value and calls it 0K, or absolute zero. Note: the “size” of 1K is the same as 1 C. To convert from C to K just add 273. K=C+273 When do