Author Archives: Eann Patterson

Sizzling sausages

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130-3071_IMGIn my post on 19th June 2013 [Closed system on the BBQ], I discussed the thermodynamics of sausages cooking on a barbeque in the context of the first law of thermodynamics.  This is an everyday example of engineering principles [see my post entitled ‘Bridging cultures’ on June 12th, 2013].  I mentioned that the energy gained by a sausage causes it to be cooked and for the water-content to boil as the temperature is raised.  The rise in temperature causes the pressure inside the sausage to increase, which is Gay-Lussac’s law in action.  When the water-content of the sausage starts to boil, the steam produced raises the pressure even further providing the sausage skin remains impervious to the transfer of matter, i.e. the steam.  The sausage as a closed system that becomes a miniature pressure vessel.

Pressure vessels fail as a result of the stresses in their wall.  In engineering, stress is defined as force divided by the area of  material carrying the force.  My sausages always fail longitudinally, i.e. they burst open with splits running along their length.  This is because the stress across the split, known as the circumferential or hoop stress, is the largest stress in the skin.

It is relatively simple to use Newton’s Third Law, about there being an equal and opposite reaction for every action force, to show that the circumferential stress is larger than the longitudinal stress; but it is a level of detail beyond what I feel is appropriate here.  Bursting sausages are a good illustration of Everyday  Examples of Engineering, which became the ‘poster-child’ of the NSF-funded project that developed them in the USA .  The pedagogy underpinning the use of Everyday Examples is explained in detail in a paper in the European Journal of Engineering Education (vol 36, pages 211-224, 2011) and a 5Es lesson plan is available here [for more on 5Es lesson plans see my post entitled ‘Disease of the modern age’ on June 26th, 2013].

You can see a video of me talking about these sausages at http://www.youtube.com/watch?v=nsSxKuRo4H0

EJEE paper: http://www.tandfonline.com/doi/abs/10.1080/03043797.2011.575218#.UbG9TZyPMx4

Disease of the modern age

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hot flatThomas Friedman described ‘continuous partial attention’ as a disease of the modern age in his book ‘Hot, Flat and Crowded – Why we need a green revolution and how it can renew America’ [Farrar, Straus & Giroux, New York, 2008].  Most university students suffer from this disease, which makes it difficult for lecturers to attract and hold their attention.  An NSF-funded consortium of university engineering departments in the USA has developed a strategy based on using Everyday Examples of Engineering to engage students (for exemplars see http://www.engageengineering.org/?page=161 ).

A Biological Science Curriculum Study in the 1980s developed the concept of 5Es as a framework for lecture or lesson plans based on the earlier work of Atkin and Karplus [Atkin JM, & Karplus R, Discovery or invention? Science Teacher, 29(5):45, 1962].  The 5Es are: ENGAGE, EXPLORE, EXPLAIN, ELABORATE and EVALUATE.

I have edited a series of lesson plans which combine the 5Es framework and Everyday Examples of Engineering principles [see http://www.engineeringexamples.org ], which are intended to support lecturers who want to use these examples in their teaching.  The lesson plans describe how the engineering principles can be applied and explained as well as providing worked analyses of the examples.  The worked analyses will also be useful to students although full explanations of the underlying principles are not included because it is assumed that these are well-known to the lecturer.

In my post about ‘Bridging cultures’ on June 12th, 2013, I made a commitment to write a series of posts about Everyday Examples of Engineering concepts.  When they are relevant, I intend to attached 5E lesson plans to these posts.

To quote Samuel Johnson: “the two most engaging powers of an author are to make new things familiar, familiar things new”; I aspire to this and through the lesson plans help others to achieve it in the classroom.

Closed system on BBQ

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sausagecloseupMy post of December 21st, 2012 on ‘Closed systems in nature?’ is my most popular  based on the statistics from WordPress.  These statistics led me to go back and read it again, which set me thinking along the same lines while tending the barbeque in our backyard.  A sausage is a nice example of a closed system with a boundary, or skin, that is impervious to mass or material moving across the boundary but which allows energy transfer in the form of heat.

Heat transfers into the system [sausage] through the boundary [skin] adjacent to the hot charcoal in my barbeque and heat transfers out on the opposite side.  Heat is simply energy transfer that occurs along a temperature gradient or across a temperature difference, from a higher to a lower temperature.

The temperature difference between the hot charcoal at about 375 degrees Centigrade and a sausage starting to cook at about 70 degrees is larger than the difference between the sausage and the air above it at say 35 degrees Centigrade, so more heat [energy] is transferred into than out of the sausage.  The difference between the energy in and out is used to heat and cook the sausage including starting to boil the water-content and trigger chemical reactions associated with cooking.  This is a manifestation of the first law of thermodynamics for the closed system, i.e. heat transfer in minus heat transfer out equals the change in the energy content of the system.  The net flux of heat into the sausage causes it to get hot and be cooked.

You can’t avoid thermodynamics, it gets involved in everything!

Bridging cultures

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cpsnowAs long ago as 1959, Sir Charles Snow identified two cultures in modern society, which could be summarised as those that understand the consequences of the second law of thermodynamics and those that don’t [see my post entitled Two Cultures on March 5, 2013].

The main aim in writing this blog is to help in bridging the gap between these cultures by commenting on and explaining engineering concepts, ideas and principles in a way that non-engineers can appreciate and might read.  One of the reasons for the gap between the cultures within our society is that ‘technology is really a way of thinking’ [see reference below].  Engineering educators spend a lot of time teaching prospective engineers how to think and, in particular, how to solve engineering problems.  However, these same educators often forget when introducing engineering students  to the principles of engineering for the first time that the students are not familiar with the language or culture.  The students are just starting to cross the gap and their educators, who are on the other side of the gap, fail to appreciate the width of the gap.  The result is that educators fail to engage the students which results in poor recruitment and retention of engineering students.  This failing is recognised by some people, see for instance http://www.engageengineering.org/

One solution to help students cross the gap is to use familiar everyday examples to explain engineering concepts.  I have made a short video about the underlying pedagogy together with some examples that you can find at http://www.youtube.com/watch?v=qAh4QHC8ya0&feature=youtu.be .  There is also a series of booklets [ http://www.engineeringexamples.org/ ] designed to support university teachers who want to teach in this way.  I plan to rewrite the examples in these booklets as periodic posts on this blog for a wider, non-technical audience.  So watch this space!

‘Technology is really a way of thinking’: http://www.atse.org.au/Documents/Publications/Reports/Education/ATSE%20Technology%20Education%20A%20Way%20of%20Thinking%202004.pdf