Ah, I see now. I forgot I had to keep the direction of acceleration consistent for both equations. In that case I found Ff to be approximately .009N, which certainly makes more sense as a friction force between a smooth ramp and small smooth wheels. I understand what you're saying in regards to...
I have a question regarding a friction experiment, so here's what I have so far:
Homework Statement
Calculate the approximate force of friction between the wheels of a cart and a ramp it is rolling on by only using the cart's mass and different values of acceleration up and down the ramp...