Since friction is in the opposite direction as the direction of movement, wouldn't you expect the work to be negative? When I put it in the work formula, W = F * cos(180O) * d it comes out positive because F is negative and cos(180) is negative too. This means that if I have another force pulling something across a surface, then it would do more work if there is friction. I read somewhere that the work is equal to the change in kinetic energy between two points but I was working on some homework and I realized that the only way I could get the right answer is if I made is so that W = F * cos(0O) * d (instead of theta = 180) in the friction work formula; that way friction gives negative work and when I add the two it equals to the change of kinetic friction. Is there anything wrong in my original reasoning that W = F * cos(180O) * d? I'm generally confused about work, could someone explain to me how it works?