# rolling friction

• Jun 5th 2007, 01:44 PM
rcmango
rolling friction
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

thankyou.
• Jun 6th 2007, 04:12 AM
topsquark
Quote:

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

thankyou.

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

-Dan
• Jun 6th 2007, 09:07 AM
Jhevon
Quote:

Originally Posted by topsquark
Rolling friction is defined just like kinetic friction:
$\displaystyle f_r = \mu_rN$

-Dan

i suppose $\displaystyle f_r$ is friction, $\displaystyle \mu_r$ is the coefficient of friction, and $\displaystyle N$ is the force in Newtons? Well, no, they would use $\displaystyle F$ for force right? what do the variables mean?
• Jun 6th 2007, 09:38 AM
topsquark
Quote:

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

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

$\displaystyle f_r = \mu _r N$
where
$\displaystyle f_r$ is the force of friction
$\displaystyle \mu _r$ 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