Physics 15: 1-4 The Laws of Thermodynamics
Text Reading: Giancoli, Physics - Principles with Applications, Chapter 15: Sections 1 to 4.
- Section 1: The first law of thermodynamics is the conservation of energy. For any well-defined system, the total energy of the system remains constant as long as no matter or heat flows across the boundaries of the system. If either heat flows or matter changes shape with respect to the outside world, then the change in energy is the sum of the heat flow Q, plus the work done on the system by the environment (or vice versa). For a contained system, "work done" requires moving the boundaries of the system. So to do work, the volume of the system must change. As with other conservative systems, we don't need to work about the pathway for this process, only about the states before and after the change. The conservation of energy means that energy cannot be created: you can never get more energy out of system than you put in. Or to put it another way: you can't win.
- Section 2: Applications of the the first law involve looking at heat flow and work done under different conditions. We graph pressure vs. volume as we hold temperature constant (isothermic), hold pressure constant (isobaric), hold volume constant (isochoric or isovolumetric) and if no heat flows (adiabatic) so that we can determine which processes involve more work W = PΔV. Note that from this definition, isovolumetric (or isochoric) process involve no work, since ΔV = 0. Changes in pressure under these conditions results from heat flow due to temperature change.
- Section 3*: When animals do work, the rate at which energy is consumed changes depending on the amount of work done. Measurements of of kcal/h are measurements of energy/time, or power, and can be converted to joules/second or watts.
- Section 4: The second law of thermodynamics says heat tends to flow from a hot object to a cold object but not the other way. If you put energy into a system, you can't get all of it back out, so you can't break even.
- First Law of Thermodynamics
- Work done in Volume Changes
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Energy and Reversible Reactions: Experiment with different numbers of molecules in each chamber, and different heat settings.
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Heat, Work, and the First Law of Thermodynamics gives a brief introduction to the research into energy inspired by the demands of the industrial revolution.
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