Quick friction concept question

[jcpwn2004]

Homework Statement

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.

Homework Equations

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.

 

[catkin]

Try imagining the forces resolved into horizontal and vertical components. Does that help?

 

[ZPower]

2. Homework Equations ,

Force of Friction = mu*Normal ForceSo if u are pulling bellow the horiziontal, u are pusing the box into the ground, thus increasing the normal force => increasing friction.

If you pull above horizontal, then u are pulling up the box => less Normal force => less friction

make sense?

question ? ask me

ZPOWER