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If you’ve heard of the rubber band heat engine and always wondered how it works, you are surely not alone. Given its status as little more than a novelty item used for demonstrating the first law of thermodynamics, the engine itself has no real relevance outside of academic circles. Still, it is sometimes useful for even laypeople to have a better understanding of the way in which energy can be converted from one form to another, achieving effective work in the process. Since heat is one of the most abundant forms of energy on the planet, something as simple as a rubber band engine has much to teach us about the way in which our world operates.
The engine itself makes effective use of thermodynamics’ first law, which has to do with the conservation of energy. In effect, it is the first law that tells us that heat is, in fact, energy. It is, however, a form of energy that has no real order to it, which means that we must convert it to other more useful and ordered forms of energy if it is to be of benefit to us in any way other than providing us with warmth on a cold day. This conversion of energy from one form to another is more commonly referred to by scientists as work.
Most people are unaware of the rubber band’s potential for converting heat into energy. Rubber is a strange compound in this regard. Most objects and materials find themselves expanding when they encounter heat – this includes wood, metal, and almost every other substance. The atoms begin to dance in a supercharged, hyper-excited fashion, and the next thing you know the distance between the atoms grows, thus expanding the object itself. Rubber, on the other hand, actually contracts when confronted with heat. A rubber band heat engine makes use of this fact to transfer heat energy from the band in such a way that the band can be used to do work.
These types of heat engine always revolve around the rubber band being attached to some sort of object and a series of gears. When the heat is applied to the band, it contracts, and thus lifts the object to which it is attached. While this is a clear and easy to understand example of the first law of thermodynamics in action, it is limited in its practical applications due to the effects of thermodynamics’ second law. That law basically says that even though you can convert mechanical energy to heat, the opposite is not entirely true. The result is that every attempt to convert heat into usable, efficient energy invariably results in a waste of the basic heat unit.
So, is there a real use for the rubber band heat engine? Absolutely! It is an important tool for teaching others about the principles of energy. Whether you have children or are an educator, obtaining a basic rubber band engine of this kind can be a simple way to get the children in your care engaged in thinking about some of these important energy issues.