A coin rests without slipping on a horizontal disc rotating with constant angular speed. The direction of static friction on the coin is:
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A coin rests without slipping on a horizontal disc rotating with constant angular speed. The direction of static friction on the coin is:

G1 Physics · Accepted Answer

The coin executes uniform circular motion, so its acceleration is radially inward with magnitude a_c = ω²r. The only horizontal force available to provide this centripetal acceleration is static friction. Hence fₛ = mω²r, directed radially inward.