Entropy in Layman's Terms

Hi Purpledawn,I'm coming in in the middle and may not be able to help, but let me try.Concerning your example of your grandson spilling his drink, cleaning it up, then going back to your chair, that's not really equivalent to what is being explained. Let me try a different visual.Imagine a water wheel such as would be used in the 1800's to run a grinding mill for grain. There are many historic mills still around, and here's a picture of one (click to enlarge): Now imagine that all the water we have to drive the wheel is in a water tank, and the tank has a valve that is currently closed. If we open the valve then water will flow from the water tank down the sluice and onto the wheel, thereby making it turn. The water in the tank has potential energy, the potential to do work by driving the wheel.So let's imagine that we open the valve and let the water drive the wheel. The water flows down the sluice and onto the wheel and the wheel begins to turn. The wheel turns for a while, then the tank runs out of water and the wheel stops turning. All the potential energy in the water that was in the tank has been transformed into kinetic energy when it made the wheel turn (and presumably turned a millstone that ground some grain), and now that water is sitting in the pool below, unable to perform any more work for us. The water has no more potential energy.In thermodynamic terms we would say that when the water was in the tank that it's potential energy to do work represented a lower entropy level, and that as the water flowed down the sluice and turned the wheel then went into the pool of water that its ability to do work was used up and its entropy increased. The water can no longer be used to drive the wheel because it is below the wheel now instead of above it.One way this water could do further work is if there is another water wheel further down stream at a lower level. Another way is if we do work by filling pails with the water and lugging the water back up to the tank and pouring it in. After we've expended all this work on the water it will again have a great deal of potential energy in the tank, and we can again open the valve and let the water do work by turning the wheel again.Hope this helps.--Percy

Hi Purpledawn,When the water is in the water tank the system is not in equilibrium because the water can flow down the sluice and water wheel and do work. When the water is in the pool at the bottom of the wheel the system is now in equilibrium because the water can flow no lower and has no more potential to do work. It is in it's lowest energy state.Of course, if the pool at the bottom of the wheel isn't really the lowest point then the water has the potential to do more work. For instance, if the pool is actually a river shore then the water can flow further down stream and do more work along the way, including flowing down another water wheel that might be present at the river's edge.When Rrhain mentioned an ice cube and boiling water he was giving a heat flow example of thermodynamics, where it's heat that is flowing from hotter to colder instead of water flowing from higher to lower. Heat can only flow from hotter to colder, not in the opposite direction, so heat will flow from the boiling water to the ice cube. When the ice cube and the boiling water are the same temperature then heat can no longer flow and the system is in equilibrium, just as in the water wheel example where when the water is all in the pool at the bottom of the wheel it can no longer flow and the system is in equilibrium.The reason the example with you in the chair is not analogous to heat or water flow is that you start and end in the exact same position. In the water wheel example the water began in the tank at the top and ended up in the pool at the bottom. In the heat flow example the heat began in the boiling water and ended up evenly distributed throughout the water, including the ice cube which melted and joined the water in the pot. But you started in the chair and ended in the chair.If you like you can try and refine your example, but it feels like you're headed in the wrong direction. Part of the problem may be that when Rrhain uses the word "disparity" he only means difference, as in the difference in heat between the boiling water and the ice cube, while you're thinking of "disparity" as a disturbance, as in your nephew spilling something.--Percy

Oh, no, the water wheel is pure thermodynamics, not an analogy. Just as the heat content of water has the potential to do work (e.g., steam pushing against and moving a piston in a steam engine), the potential energy of water in a water tank also has the potential to do work (e.g., turning a water wheel as it flows downhill).Chemical bonds also store energy that has the potential to do work. ATP is an energy containing molecule used by your muscles when you do work. When you clean up your nephews spill you are converting the chemical energy in ATP molecules into the kinetic energy of the movement of your body. As you clean the spill the energy in the ATP molecules is being distributed more and more evenly into the environment around you in the form of increasing body temperature that is radiated away as heat into the air and in the form of kinetic energy of other things you set in motion like sponges and towels and in the form of increased heat caused by friction as you rub the rug. When you've finished cleaning the spill you have lessened your ability to do work, and the energy of the work you've done has mainly just increased the temperature of your surroundings.By the way, whether a clean or dirty rug is higher or lower in its potential to do work (lower or higher entropy) is probably impossible to figure out. Because of the analogies that are often used when explaining thermodynamics to laypeople, it is a common misconception that a dirty room has higher entropy than a clean room. In reality, if we define our original system as the dirty room with you in it, then after you've used all that energy putting things away and dusting and cleaning and so forth, you and the now clean room have higher entropy because of all the energy you used that was at one time concentrated in your body and is now more evenly distributed into your surroundings.--Percy

Oh my.I think I maybe shouldn't have said anything. I'm really sorry, I think I've only made things harder for you. Ignore my posts and continue working with what Rrhain said.--Percy

--Percy