Uniform Circular Motion- Centripetal Force

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

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