If ${\mu _s},\,{\mu _k}$ and ${\mu _r}$ are coefficients of static friction, sliding friction and rolling friction, then
If ${\mu _s},\,{\mu _k}$ and ${\mu _r}$ are coefficients of static friction, sliding friction and rolling friction, then
${\mu _s} < {\mu _k} < {\mu _r}$
${\mu _k} < {\mu _r} < {\mu _s}$
${\mu _r} < {\mu _k} < {\mu _s}$
${\mu _r} = {\mu _k} = {\mu _s}$
If ${\mu _s},\,{\mu _k}$ and ${\mu _r}$ are coefficients of static friction, sliding friction and rolling friction, then
$\mu_{r}<\mu_{k}<\mu_{s}$
which implies that the rolling friction is least because of the wheel and rotating effect and the kinetic friction is in middle of the series because of its moving properties $\&$ static friction is highest because of the limiting moving properties.
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