For a uniform circular a centripetal force is required
Fc = mv2/r
Example
A disc rotates in a horizontal plane with 360 revolutions per minute
At a distance of 20 cm from the center is a block with a mass of 100 g.
Find the centripetal force on the block.
Fc = mv2/r = (0.100)( 7.39) 2 /0.20 = 27.3 N
or Fc = m ac = (0.100)( 273.06) = 27.3 N
For ac : see the previous chapter (Two dimensional motions)
Remark
This centripetal force is not a new force but it is the required net force and is directed to the center of the path.
On the block work 3 forces.
Fn normal force
W weight
f frictional force
Fn and W cancel each other
The frictional force f is the required centripetal force