1. The problem statement, all variables and given/known data A box is pulled across a rough horizontal surface with force F. Each time the box moves a distance D, howeveer the angle of F varies. Which angle causes the most/least amount of friction. An angle above/below/horizontal to the surface. 2. Relevant equations 3. The attempt at a solution I know that the least friction is caused by a force above horizontal and the most is caused by a force below horizontal but I have no clue how to explain it using physics.