RANK THE MAGNITUDE OF FRICTIONAL FORCE FROM LEAST TO GREATEST ON THE DIAGRAMS BELOW

Question

anonymous · Answer

|dw:1388870834765:dw|

anonymous · Answer

III< II< I

anonymous · Answer

were III is the last picture

anonymous · Answer

Yes, friction force = (friction coefficient) (normal force)

theeric · Answer

I agree with them! If some of the weight is negated by pulling the block up, then there's less of a normal force to make a strong friction force. See @douglaswinslowcooper 's equation, and @RaphaelFilgueiras ' rankings.

$\huge F_f=\mu F_N$

By normal force,  we mean force perpendicular to the surface.|dw:1388900891130:dw|It is the same force that the block puts downwards (opposite in direction). So it's going to be equal in magnitude to what the block is putting down on the ground. Picking the block up takes off some weight and so it decreases the normal force as well.
$F_f\huge=\Huge\mu\normalsize F_N$
Small $F_N$ means small $F_f$.

anonymous · Answer

THANK YOU GUYS FOR YOUR HELP. I AM ALSO BUSY RESEARCHING ON THE TOPIC RIGHT NOW, BUT YOU HAVE MADE THE TASK A MUCH EASIER ONE NOW :)

theeric · Answer

Awesome! Good luck, and feel free to ask questions! I'm sure people on OpenStudy will be around to help (at least eventually).