Friction

1
Friction
Because the box slides down the ramp friction
acts up the ramp well call it FF
Because the block pushes on the ramp the ramp
pushes back on the block well call this
reactive force FN
Part of its weight (Fw) acts down the ramp
well call it Fp
The block has weight and it acts straight
down well call it Fw
2
Friction
FN is the part of Fw acting perpendicular to the
surface
FN
FF
FP
FN -FN
Fw
3
Friction
Convert to a vector diagram! Move component Fp
to the head of FN
4
Note that Fp is perpendicular to FN
Remember that q is the same as the angle of
the ramp!
q
Therefore
Fp sine q x Fw
and,
FN cosine q x Fw