This lecture accompanies what you just read. It talks about the equations of kinetic and static friction forces, and the concepts behind friction itself. Watch the video until the 6:12 mark, where Clements begins discussing springs and other material we will cover in another Saylor course, PHYS102 Introduction to Electromagnetism.
Source: Greg Clements, https://www.youtube.com/watch?v=UjdCpnRTwbw
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