calzoneman/Golfram-Alpha — comment on commit e4989c9855d6a39f9f7411d359e0cded4abf0c93
File: golfram/core.py line 337
By calzoneman:

I think it would make more sense to initialize direction as the positive normalized vector and set friction = self.friction * direction * -1. This makes it more obvious that friction is opposite direction whereas before I was confused about why you negated direction.