Biomechanics

Do the locomotion: personal explorations of Froude number

By Jessica Bolker, University of New Hampshire


Type of Resource Class activity 
Topic Locomotion/motility 
Taxa Vertebrate 
Organizational Level Organismal 
Estimated time to do activity Roughly an hour 
Background required/level Prior introduction to gait, Froude number – or this activity could serve as the introduction. 
Role of activity in your course A late-spring outdoor lab that provided an opportunity to collect some data to plug into the equation for Fr. 
What students might learn from this course or activity This activity is very straightforward, so it’s a good opportunity to remind students of fundamental issues about consistency, measurement, precision, significant figures, etc. as well as review Froude number and its components. 
Special tools, equipment or software needed Meter sticks or tape measures for measuring leg length; long tape measures or rolling wheels for measuring traveled distances; calculators; stopwatches; chalk (useful for marking off distances); at least one pair of crutches; possibly a set of ankle weights; level and gently sloped smooth surfaces for locomoting over.

 
Safety precautions, possible permissions necessary None 
Miscellaneous advice - pitfalls to avoid Make sure students pay attention to consistency of measurements (especially of leg length), and of gaits. Watch how they figure out “leg length” for crutches, and intervene if necessary.

For measuring slope, it’s extremely convenient to find a brick building located alongside a smoothly sloping sidewalk: use a single course of bricks as a level line, start following it at ground level on the uphill end of the building, and measure how high above the ground it is at the downhill end. Divide by the length of the building to get slope.

If time is limited, students can collect data during lab period and then crank through calculations at home. It is best to have everyone collect data at the same time/sites, though, for consistency.

Students really enjoyed this lab: it made an otherwise abstract, dimensionless number very real; they had a lot of fun; and as one commented, “I liked being outside and actually being the experiment.”

Additional possibilities, which I have not yet tried: a set of ankle weights (sporting goods outfits sell them) to see what that does to the transition point….Also bringing in race walking, where someone deliberately tries to maximize stride length - one can get into a pace that’s more costly than running at the same speed, giving a sense of the energetic advantage of the transition. If everyone in the class is about the same height, students might be asked to invite a few exceptionally short (kids?) and exceptionally tall individuals to participate. (Perhaps next time I’ll invite my offspring.)
 
Frequently asked questions by students Q: How come my calculated Fr is way off anything in lecture or the book, or what anyone else got? A: Check units, check dimensions, check math…. 
Description Easy, low-key, outdoor data collection and straightforward calculations centered on terrestrial locomotion and the different components of Froude number. 
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