Below are descriptions of several non-traditional class meetings used by Prof. Hrenya to teach various topics in a course in undergraduate fluid mechanics .  The content provided below is intended to be shared among educators for use in their own classroom with little time investment.  A manuscript on this work has been accepted for publication in Chemical Engineering Education, and reference information will be posted here when available.  Feedback and suggestions are welcome - send to hrenya@colorado.edu.


Contest:  Tube Flow Experiments on YouTube

Knowing how to identify and solve fluid mechanical problems using the mechanical energy balance is an essential tool for engineers with a training in fluid mechanics.  Typically, the basic equation, friction factor charts, and tables with loss coefficients for fittings, etc. are introduced in one lecture, with another lecture dedicated to example problems.  The latter is justified given the different level of complexitiesthat can be encountered  - e.g., a simple plug-and-chug solution when finding the pressure drop in laminar flow to a trial-and-error solution for sizing pipe diameters in turbulent flows.

In this class period, an alternative to the traditional lecture on example problems for the mechanical energy balance is given.  Namely, a "contest" is set up for small groups to correctly predict the outcome of a tube flow experiment.  The class takes 3 parts:  (i) introduction of the tube flow experiment, including the specific measurements to be taken, (ii) small groups work to make predictions of the experimental outcome, (iii) experiment is run, with small prizes given to groups with best predictions.

The benefits of this class include:

  • active learning with ad hoc group of peers working on problem solution
  • contest format instills high level of motivation toward problem solution - this is the highest-energy class of the semester
  • in-class experimental data provides verification of "correctness" of mechanical energy balance
  • complexity of example problems not sacrificed, as three-part experiment provides range of straightforward to complex calculations

Below is the course content for use by educators in their own class.

  • A YouTube video introducing the experiment to the class:  click here for YouTube video
  • An Excel spreadsheet which can be used to record the predictions by each group, the experimental results, and then determines contest winners:  click to download Excel spreadsheet for tube flow contest
  • A separate video showing the experimental being run and a "solutions" document with detailed calculations from the mechanical energy balance; interested educators should email hrenya@colorado.edu with a request for this video from their university email address.

End-of-Semester Project:  Puzzling Questions in Fluid Mechanics


The last week of the semester is typically reserved for course review, since the introduction of new material the week prior to final exams is challenging at best.  In this variation on that theme, small groups of students answer unique questions related to a puzzling fluid mechanical phenomena seen in everyday life, the answers to which draw on the course content throughout the semester:  buoyancy, turbulence, drag force, hydrostatics, surface tension, mechanical energy balance, dimensionless numbers, surface tension, etc.  The questions, taken from the listing below, are assigned several weeks prior to the end of the semester.  During the final week of class, each group turns in a short report on their findings, and gives a 6-10 minute presentation to the entire class, in which illustrative calculations, demonstrations, and videos are encouraged.

The benefits of this class include:

  • course material presented throughout semester is reinforced via peer instruction, including some surprisingly creative demonstrations
  • students are exposed to a wide range of everyday applications of fluid mechanics, including headlines from the news
  • working with self-selected group on question with open-ended nature
  • practice on written and oral communication skills, with feedback from instructor

Below is the course content for use by educators in their own class.

An example of related project files are included here: click to download project description, signup sheet, and grading sheet .  Below is the list of puzzling questions in fluid mechanics - feel free to send suggestions for additions to this list to hrenya@colorado.edu.

  1. Why is sand used in an hourglass instead of a liquid?
  2. Why does a golf ball have dimples?
  3. Why does a knuckleball appear to “dance”?
  4. On 15 Oct 2009, a 6-year old boy named Falcon Heene (aka “Balloon Boy”) was reported missing. Authorities were led to believe that he was in a home-made balloon contraption that was constructed with tarps (which are usually made from High Density Polyethylene) and duct tape and then filled with helium. A day of hot pursuit of the balloon by law enforcement, medical professionals, and the media pursued. When the balloon landed, the boy was not inside and was later found hiding in an attic.  Should a graduate of this class have been hired to determine if the home-made balloon could support the weight of the boy? Some useful information is: (i) authorities said the silver balloon, 20-feet long and 5-feet high, at times reached 7,000 feet above the ground while adrift. (http://www.cnn.com/2009/US/10/15/colorado.boy.balloon/index.html ), and (ii) the balloon can be estimated to be an oblate spheroid.  (contribution by class member Brittany Jo Michael, 2010)
  5. Why can a sail boat travel faster than the wind?
  6. Why can a water bug walk on water when I can't, and how big could the bug be?
  7. Why is it easy to float in the Dead Sea and not in the ocean?
  8. When deep sea diving, why can’t a really long snorkel be used for breathing?
  9. Prior to 2002, the CO Rockies had troubles recruiting pitchers due to the large number of home runs at Coors field, and thus high ERA’s. The thought was that at higher elevation, the air is thinner, leading to less drag, and thus balls carried further. In 2002, they started storing the baseballs in humidors, and the number of homeruns has decreased dramatically. What is the cause of the large number of homeruns prior to 2002? What is the cause of the reduction after 2002?
  10. Why is it that I get more snow on my windshield when my car is stopped at a light than when it's moving, but I get more rain on my windshield when it's moving than when it's stopped?
  11. How is body fat measured via the immersion method?
  12. How do water rockets work?
  13. At 16,000 ft. long, runway 16R/34L at Denver International Airport opened in 2003 as the longest commercial runway in the United States. Taxpayers justified the $165 million dollar expense as a necessity for ensuring Denver’s competiveness in attracting cargo and international carriers who fly heavy wide-bodied aircraft larger than those that existed when the airport opened. Why are Denver’s runways longer than those of most other airports and of six runways at DIA why does runway 16R/34L see relatively more use during summer months? (contribution by class member Danny Cromer, 2008)
  14. What basic techniques should a swimmer use to maximize her efficiency?
  15. Why do cyclists draft one another? How much does it help / hurt the leader and the followers?
  16. Why is the aerofoil (wing) shape mounted upside down in race cars relative to its mounting in planes?
  17. The Falkirk wheel is a rotating boat lift in Scotland with a capacity of nearly 200,000 gallons. Why does the weight of the wheel remain the same when boats enter or exit? Why does it consume so little power given the huge weight being moved? (contribution by class member James Prager, 2008)
  18. What are the effects of some “dirty tricks” in baseball: (i) lubrication of ball and (ii) roughening/polishing ball surface?
  19. How does a hot air balloon work?
  20. Explain how the magic trick works where you have water in a glass and then put a piece of cardboard over the glass, flip the glass and cardboard over and the cardboard stays on the glass (contribution by class member Lynn Pruisner, 2008)
  21. Why does a curve ball curve?
  22. Does the distance a discus is thrown depend more on drag or lift or both?
  23. How do self-righting and self-bailing boats work?
  24. Why does a boomerang return to the thrower?