# Dynamics in a circular disc dilemma

Experimental setup:

Imagine a circular disc kept horizontally with a frictionless groove along its diameter, in a uniform gravitational field perpendicular to disc. There is a ball in the groove currently at the center of disc. The circular disc now starts rotating with constant angular velocity $$\omega$$.

Predictions:

According to me, the ball must start moving away from the center along the groove.

Conclusions/Discussion:

Both rotating frame and non rotating frame must see ball moving and eventually fall from disc.

According to rotating frame of reference of disc, the dynamics of ball can be easily by applying centrifugal force as it is applied in rotating frame.

But according to non rotating frame of reference, the dynamics of the ball cannot be explained by centrifugal force and neither centripetal force

So, how is the dynamics of ball explained with respect to non rotating frame?

What force is pushing the ball with respect to non rotating frame?

Is there any flaws in my predictions and conclusions? Any help is massively appreciated.

• The way you posit the problem is incomplete. What about friction (or other forces) acting tangentially and not just radially?
– Gert
Feb 9, 2021 at 8:54
• I have mentioned that groove is frictionless in which ball is moving. Feb 9, 2021 at 8:55
• Feb 9, 2021 at 9:01