In this lesson, students apply their understanding of direct and inverse variation to making music with guitar strings. Students learn the equation governing the relationship between a string’s frequency, wave speed and length, and then use a digital guitar simulation to calculate the wave speeds and string lengths needed to create common chords. After playing through a simple song as a class, students construct and tune cardboard ukuleles to make their learning tangible.
Direct and inverse variation
Basic physics of string vibrations and waves
Primary CT concept: abstraction. The frequency equation uses a simplified wave speed parameter to represent physical concepts like string thickness and tension, and students abstract the detailed math away when building their physical ukuleles.
Students will be able to:
Explain how length and wave speed affect the frequency of a vibrating string
Explain how guitar strings are able to play different notes
Create a simple cardboard ukulele with strings tuned to different notes
Digital guitar simulation: http://ct.excelwa.org/ctfiles/apps/stringVibrations/stringVibrations.html
Cardboard boxes – shoeboxes will work, or you can order something like these from Home Depot: https://www.homedepot.com/p/Plain-Brown-Box-12-in-x-8-in-x-6-in-25-Moving-Box-Bundle-PRA0046B/203581824
Extra large rubber bands in at least three different sizes: https://www.amazon.com/Alliance-Rubber-08997-SuperSize-Assorted/dp/B0017D16PW/
Wooden dowels: https://www.amazon.com/Perfect-Stix-Dowel-814-80ct-Diameter/dp/B0762NP6CZ/
A guitar is optional, but will help students connect their learning to a real instrument
Suggested lesson breakdown:
This activity is more of a practice/review project than a teaching tool, and therefore works best towards the end of the unit. Students can work individually or in pairs. The timing suggestions below are estimated and are very flexible based on your students’ pace.
10min – introduction to string vibrations and the frequency formula
10min – quick practice and check for understanding
10min – calculating wave speeds in the digital guitar simulator
20min – calculating string lengths for chords in the digital guitar simulator
5min – class play-along to “Imagine” by John Lennon
15min – constructing and playing cardboard ukuleles