Measuing centripetal force

The practical today (method here: http://www.nuffieldfoundation.org/practical-physics/experimental-test-f-mv²r) showed the importance of practical skills. We identified the largest source of uncertainty (the radius was hardest to measure; v^2 the term with the largest percentage uncertainty) and decided ways of improving the practical.
Some extra resources:
http://www.nuffieldfoundation.org/practical-physics/test-mv²r-turntable
http://www.diffen.com/difference/Centrifugal_Force_vs_Centripetal_Force
https://m.youtube.com/watch?v=weeiZjz-Q-o
https://m.youtube.com/watch?v=yAfg_8OLjvs – that is not how you pronounce centrifugal