rolling friction

**rcmango** · June 5th 2007, 01:44 PM

THe coefficient of rolling friction is 0.02, then what force is needed to keep a 5 kg ball rolling at a constant speed on a horizontal surface

i know to use gravity, 9.8 m/s^2

please help me with this one.

thankyou.

**topsquark** · June 6th 2007, 04:12 AM

Originally Posted by rcmango

THe coefficient of rolling friction is 0.02, then what force is needed to keep a 5 kg ball rolling at a constant speed on a horizontal surface

i know to use gravity, 9.8 m/s^2

please help me with this one.

thankyou.

Rolling friction is defined just like kinetic friction:
$f_r = \mu_rN$

-Dan

**Jhevon** · June 6th 2007, 09:07 AM

Originally Posted by topsquark

Rolling friction is defined just like kinetic friction:
$f_r = \mu_rN$

-Dan

i suppose $f_r$ is friction, $\mu_r$ is the coefficient of friction, and $N$ is the force in Newtons? Well, no, they would use $F$ for force right? what do the variables mean?

**topsquark** · June 6th 2007, 09:38 AM

Originally Posted by Jhevon

i suppose $f_r$ is friction, $\mu_r$ is the coefficient of friction, and $N$ is the force in Newtons? Well, no, they would use $F$ for force right? what do the variables mean?

Sorry! I guess I wrote that for only the original poster, didn't I?

$f_r = \mu _r N$
where
$f_r$ is the force of friction
$\mu _r$ is the coefficient of rolling friction (typically much less than the coefficient of kinetic friction.)
and
N is the normal force on the object between the pair of surfaces inducing the friction.

-Dan

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