We examine the spinning behavior of egg-shaped axisymmetric bodies whose cross sections are
described by several oval curves similar to real eggs with thin and fat ends. We use the gyroscopic
balance condition of Moffatt and Shimomura and analyze the slip velocity of the bodies at the point
of contact as a function of θ, the angle between the axis of symmetry and the vertical axis, and find
the existence of the critical angle θc. When the bodies are spun with an initial angle θinitial > θc,
θ will increase to π, implying that the body will spin at the thin end. Alternatively, if θinitial < θc,
then θ will decrease. For some oval curves, θ will reduce to 0 and the corresponding bodies will
spin at the fat end. For other oval curves, a fixed point at θf is predicted, where 0 < θf < θc.
Then the bodies will spin not at the fat end, but at a new stable point with θf . The empirical fact
that eggs more often spin at the fat than at the thin end is explained.
1