How does force affect friction?
The frictional coefficient is just a relationship between forces: the frictional force and the applied force:
If we rearrange this expression, we see that
The applied force in the case of friction is at right angles to the direction of motion. It is the force pushing the two surfaces that are sliding over one another together.
Sometimes the applied force is due to gravity, but not always, such as when someone is cleaning a vertical window pane and must push on the cleaning cloth to provide friction between it and the glass..