About 150 years after its proposal, theoretical studies explained the physical validity of Maxwell’s demon in the context of information thermodynamics, and there have been successful experimental demonstrations of energy generation by the demon.
It almost always occurs to the skeptic to debunk out-of-balance machines by explaining why there is no torque to accelerate them. It is not easy to show the mechanical deficiency directly, but it may be the only way to convince true believers of perpetual motion, because they will not accept that any of the laws of thermodynamics apply to their machines. On the other hand it is easy to show that these machines have no source of energy other than the work done to spin them initially. The first law demands that they never accelerate, and the reality of friction means they cannot even spin uniformly forever. They simply drain energy from their initial state. Fludd's waterwheel attains its initial energy from some lacky who drew water to the upper reservoir. The out-of-balance wheel attains it from the initial push.
There is something strange about Schadewald's suggestion, however. Suppose that G doesn't decline smoothly, as Schadewald proposes. Suppose it drops suddenly as the heavy end of the wheel begins its downward roll, then stays constant. Apparently the wheel wouldn't have a kinetic energy at the low point of the cycle equal to the loss of potential energy. Where does this energy go?
There are other possibilities. Perhaps there is a permanent chemical change in addition to heat flow. That is, less dense material is incorporated continually into the crust while more dense material slowly settles to the lower mantle or core. This would act to stir the mantle. Then again, there might be other mechanical sources of energy. Tidal drag, for example, might convert some of the Earth's rotation into ciculating material in the mantle.
The plate tectonic cycle is, therefore, a heat engine. The amount of heat it rejects amounts to 0.04 watts/m2 averaged over the entire earth, which seems quite insignificant when one considers that this is enough energy for only one reading lamp every 100m2. Solar energy is ten-thousand times larger.
Perpetual motion machines of the second kind operate by extracting energy at some point in their cycle, use it for work, yet have everything return to an original state unchanged at the end of the cycle. There is the appearance of being able to deliver energy forever. Real machines and processes leave the universe changed permanently. Engineers measure this change as entropy; and the second law demands that any real process increase the entropy of the universe. Two familiar examples will show what this means.
However, this mix of plutonium isotopes can be used to produce energy for civilized use.
This fact is the technical and economic basis for breeder reactors.
Even before they knew there was a first law, engineers observed that machines perform less work than the amount of energy they consume. In particular, heat engines always reject some waste heat. For example, an automobile engine always heats the surrounding air, heats water in its radiator, expels heat through its tail pipe, and so forth. The second law guarantees that no clever design could eliminate these losses completely.
For example, if a car passes an observer who is stationary, then the speeds of both objects are relative to each other, and hence the car possesses kinetic energy with a positive value.
What this has to do with engines is not obvious, but I'll try to explain it now. To make a heat engine work we must make heat energy flow into it. The only way to do this is to connect it to a reservoir that is hot. Heat energy will flow into the engine, which converts some of this heat to work. However, doing nothing more than absorbing heat would decrease entropy. So the heat engine has to expel waste heat to another reservoir, and, the only way to do this is have a reservoir that is colder than the engine. Also, because the engine used some of the heat energy for work, there is less heat to expel to this cold reservoir than was absorbed from the hot one. Thus, to use rejected heat to offset the decrease of entropy from absorption, the reservoir for waste heat has to be much colder than the hot one. The more temperature difference there is between the two reservoirs, the more work we can perform with the engine and still manage to increase entropy. Large temperature differences result in a large "thermal force" to run a machine efficiently.
The first law demands that all machines have a source of energy, but, it doesn't limit how much of this energy a machine can use for work. Could it all be used for work? Could a machine have 100% efficiency?
Perpetual motion machines of the first kind violate this idea of energy conservation. The most obvious machine like this is the perpetual lamp. It produces heat or light, but never drains an energy reservoir to do so. It procures energy from nothingness. Another simple example is the unbalanced wheel, especially the unbalanced wheel with a brake to keep it from accelerating. If a tiny push of the wheel were to set it accelerating, then the wheel would have more energy in its rotation than was put into it with work from the push. Once again, it procures energy from nowhere.
This essay presents the concept of energy by discussing the two major types of energy, the various forms it could take, including renewable sources of energy, energy conservation and above all it talks about the safest and cleanest alternatives....