Tag Archives: fluids

Singing in the rain

Followers of this blog might have deduced that I live within sight of the sea, which means that it is nearly always windy.  After a rain storm the streets of the city are usually littered with broken umbrellas.  I suspect that most of these belong to the many tourists that visit Liverpool, because local residents know that the wind will wreck any umbrella that you are brave enough or foolish enough to put up.

It is relatively straightforward to estimate the forces involved in holding an umbrella up in a gale by using control volume analysis.  The lesson plan below includes this Everyday Engineering Example together with two more control volume analyses.

Momentum 5EplanNoF5_momentum

The title of the posting is pretty tenuous this week: Gene Kelly sings ‘Singin’ in the rain’ without an umbrella in the film of the same name, see www.youtube.com/watch?v=D1ZYhVpdXbQ – well its difficult to be creative all of the time, or even some of the time!

See also the Everyday Engineering Examples page on this blog for more lesson plans and more background on Everyday Engineering Examples.

Reducing tension

bubbleHave you ever tried to float a paperclip in a bowl of water?  It is quite difficult but possible if you put the paperclip on a piece of tissue paper and carefully place the tissue paper with the paperclip onto the surface of the water; then, using a pencil slowly push the tissue underwater and, with a little bit of luck and practice, the paperclip will be left floating on the surface of the water.  The surface tension of the water counteracts the gravitational force on the paperclip.  This is the same mechanism that allows some insects to ‘skate’ across the surface of ponds.

Detergent is a surfactant which reduces the surface tension of the water.  So, if you drop a little bit into your bowl of water the paperclip will sink because the surface tension is no longer sufficient to support it.

This is not an experiment to demonstrate in class because it is too delicate and too small for students to see but students can do it for themselves at home.  An alternative for demonstrating surface tension effects is to blow bubbles using a detergent solution.  These two ‘Everyday Engineering Examples’ are described in the lesson plan below and you can watch a video clip about it at www.youtube.com/watch?v=BRyQvGEQUt0


See also the Everyday Engineering Examples page on this blog for more lesson plans and more background on Everyday Examples.

Floods: an everyday example

floodingI wrote this post before going to the concert at the Philharmonic Hall which inspired the post on February 5th [Rhapsody in Blue].  So, this post is not quite as timely as planned originally but it is still raining frequently here and the Somerset levels remain flooded.

Since before Christmas news bulletins in the US and UK have been dominated by reports of extreme weather events.  Earlier this month the sea on the south coast of the England swept away a substantial length of the main railway line between London and the South-West of the country.  Large areas of the south of the UK have been flooded by storms that rolled across the Atlantic having first caused disruption in North America.  There seems to be plenty of everyday evidence from these events that our climate is changing and this appears to have been confirmed by the Chief Scientist at the UK Metrological Office.

The Intergovernmental Panel on Climate Change has stated ‘Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.  The atmosphere and oceans have warmed, the amounts of snow and ice diminished, sea level has risen, and the concentrations of greenhouse gases have increased.’  They go on to say ‘It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-twentieth century’.  Despite these assertions, our governments have been unable to make significant progress towards limiting global warming to 2 degrees Celsius compared to pre-industrial levels.  The delegations from most of the developed countries walked out of talks at the Warsaw climate conference last November, followed by representatives from the Green groups and NGOs the next day.  As a consequence, Kofi Annan [Climate crisis: Who will act? in International NYT  November 25, 2013] has called for a global grass-roots movement to tackle climate change and its consequences.  We need to act as individuals whenever we can to reduce global warming and mitigate its impact both directly in our personal and professional lives and indirectly by lobbying our political and industrial/commercial leaders.

In the UK, politicians and the media are beginning to talk about the need for engineers to protect us against flooding and some engineers are responding by highlighting that the cost will be very high and that if climate change continues then we will have consider abandoning some areas.

At a simpler level, those us working in the classroom can use the flooded roads and overwhelmed drainage systems to create topical, and perhaps increasingly everyday, examples focused on flow in drainage ditches, gutters etc., as in the lesson plan below.


See also the Everyday Examples page on this blog for more lesson plans and more background on Everyday Examples.