A coin is placed on a horizontal disc at distance r from the centre. The disc rotates with constant angular speed ω. If ω²r becomes greater than μₛg, the coin tends to slip relative to the disc:
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A coin is placed on a horizontal disc at distance r from the centre. The disc rotates with constant angular speed ω. If ω²r becomes greater than μₛg, the coin tends to slip relative to the disc:

G1 Physics · Accepted Answer

For circular motion with the disc, the coin requires inward friction mω²r. The maximum available static friction is μₛmg. If mω²r > μₛmg, static friction is insufficient to maintain the required circular motion. In the rotating frame of the disc, the coin therefore has an outward slipping tendency.