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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 = 14.7 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 = 14.7 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, e.g. 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 1.8 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
