(sorry about the misspelling of principal as principle - oops!) This demonstration shows a fascinating observation about the rotation of a tennis racket (or ping-pong paddle) is that the racket flips over if rotated freely about one of its primary axes. This is a result of Euler's Equations of Motion and the moments of inertia about the various axes being time-independent. The so-called "Tennis Racket Theorem" applies to the case where the moments of inertia about the principal axes are spaced: I1 ≪ I2 ≪ I3. The theorem states that rotations about axes I1 and I3 are much more stable than about axis I2, even though I2 may be very close to I3 in value.
