# Popping balloons

Balloons ripe for popping!

Each year in my thermodynamics class I have some fun popping balloons and talking about irreversibilities that occur in order to satisfy the second law of thermodynamics.  The popping balloon represents the unconstrained expansion of a gas and is one form of irreversibility.  Other irreversibilities, including friction and heat transfer, are discussed in the video clip on Entropy in our MOOC on Energy: Thermodynamics in Everyday Life which will rerun from October 3rd, 2016.

Last week I was in Florida at the Annual Conference of the Society for Experimental Mechanics (SEM) and Clive Siviour, in his JSA Young Investigator Lecture, used balloon popping to illustrate something completely different.  He was talking about the way high-speed photography allows us to see events that are invisible to the naked eye.  This is similar to the way a microscope reveals the form and structure of objects that are also invisible to the naked eye.  In other words, a high-speed camera allows us to observe events in the temporal domain and a microscope enables us to observe structure in the spatial domain.  Of course you can combine the two technologies together to observe the very small moving very fast, for instance blood flow in capillaries.

Clive’s lecture was on ‘Techniques for High Rate Properties of Polymers’ and of course balloons are polymers and experience high rates of deformation when popped.  He went on to talk about measuring properties of polymers and their application in objects as diverse as cycle helmets and mobile phones.

# Dream machine

Painting by Katy Gibson

A machine that can do work indefinitely without any external input of energy.  It would solve the world’s energy problems, eliminate global warming and make the inventor very rich.  There have been so many attempts to design such a machine that a classification system has been established.  My machine, that does work indefinitely with no energy input, would be a perpetual motion machine of the first type because energy is not conserved – a contradiction of the first law of thermodynamics.  The second type contravene the second law of thermodynamics, usually by spontaneously converting heat into work, and the third type eliminates friction and, or other dissipative forces.

I said ‘my machine’ in the sense that I have an on-going sporadic correspondence with the inventor of a machine that is claimed to produce ‘power above the primary power that drives it’.  It is an epistemic impossibility, which means that it cannot exist within our current understanding of the real world.  In other words, if a perpetual motion machine was to be proven to exist then the laws of thermodynamics would have to be rewritten.  This would probably lead to an invitation to Stockholm to collect a Nobel prize.

Such arguments make no difference to inventors of perpetual motion machines.  Many appear to start from the premise that the laws of thermodynamics have not been proven and hence they must not be universally applicable, i.e. there is space for their invention.  Whereas the laws of thermodynamics form part of our current understanding of the world because no one has demonstrated their falsity despite many attempts over the last two hundred years.  This is consistent with the philosophical ideas introduced by Karl Popper in the middle of the last century.  He proposed that a hypothesis cannot be proven to be correct using observational evidence but its falsity can be demonstrated.

So, inventors need to build and demonstrate their perpetual motion machines in order to falsify the relevant law of science.  At this stage money as an input usually becomes an issue rather than energy!

The painting by Katy Gibson is from a series made as part from an art and engine collaboration between Okemos High School Art Program and the Department of Mechanical Engineering at Michigan State University.