Skip to 0 minutes and 4 secondsThe first law of thermodynamics requires that energy is always conserved. We convert it into many different forms, mechanical work, thermal energy, kinetic energy, potential energy, energy stored in matter. And in the past three weeks, we have looked at how we can balance these forms and the transformations between them for a system. And we can define the system to suit the analysis we want to perform. However, the first law makes it very clear that it's impossible to invent a machine that does useful work or generates heat without depleting energy from some source. In other words, we can't have machines that create new energy. Scientific laws cannot be proven, only demonstrated to be false or inappropriate.
Skip to 0 minutes and 56 secondsIn the more than 160 years, since Mayer first expressed the first law, no exceptions have been found. This has not stopped inventors dreaming of fame, wealth, or simply a solution to the world's energy crisis from proposing machines that dodge this law and produce more energy than it takes to power them. None of them work in a real, physical world, and they are known to us as perpetual motion machines of the first kind. There are also perpetual motion machines of the second kind. These contravene the second law of thermodynamics, which we're going to study next week.
Skip to 1 minute and 37 secondsThe second law can be expressed as, it is impossible to construct a machine that, operating in a cycle, will produce no other effect than the extraction of heat from a source and the production of an equivalent amount of mechanical work. An alternative form of the second law is, it is impossible to construct a machine that, operating in a cycle, will produce no other effect than the transfer of heat from a cooler body to a hotter one. These alternative versions of the second law can make it difficult to appreciate and hard to apply. In essence, we can't move thermal energy around without losing some. Nature demands a share of any heat that we transfer.
Skip to 2 minutes and 25 secondsIt can be difficult to spot exactly how a perpetual motion machine violates the laws of thermodynamics. Inventors can be devilishly clever in designing machines. So I'd like to challenge you to design the most elegant, imaginative perpetual motion machine that you can conceive. To get you started, here is one from Raymond Friedman's book on "Problem Solving for Engineers and Scientists, A Creative Approach," published by Van Nostrand Reinhold.
Skip to 3 minutes and 0 secondsIt's an underwater rotating device. A series of cylinders with airtight and watertight pistons are attached to a continuous chain belt which is looped around the pair of sprocket wheels. When the open end of the cylinder is upwards, the piston slides to the closed end. But when the open end of the cylinder is downwards, the piston slides down to close off the opening, creating a vacuum in the cylinder and causing the cylinder to displace a large volume of water. Then, the buoyancy drives these cylinders up so that the sprocket wheels turn anti-clockwise and energy can be extracted.
Skip to 3 minutes and 39 secondsOnce set in motion, the combination of gravity on the left and buoyancy on the right will keep the device running forever, or will it?
Introduction to perpetual motion design project
I would like to challenge you to design the most elegant, imaginative perpetual motion machine that you can conceive. There is no prize as such, but a certain amount of cache if you win!
To join in, simply sketch your idea on to a piece of paper, take a picture of it and upload it to this site. Include a brief description of the working of your idea, and remember to head it with your name. I have done the first one as an example for you. You can vote (once only) for who you think is best by writing their name in the discussion section. The competition will close on March 13 2016 when I will count up who has the most votes, and send you the results in the end of course e-mail. Good luck!
© The University of Liverpool