In our recent article analyzing the steady-state motion of Hurricane Balls,1 we neglected to reference a very interesting analysis by William Case.2 In this article, Case presents an elementary discussion of a gyroscope that relies only on conservation laws and makes no use of Lagrangians or Euler angles. Such an analysis is relevant to our analysis, particularly Appendix B 2, and we regret not having discovered and referenced this thoughtful article.

Interestingly, as we read over this article we came to realize that we made an incorrect comment in our final endnote (Ref. 23), where we imply that the motion of the center of mass is neglected in the standard treatment of a spinning top with a fixed point of contact. This hasty comment came about because our expression for the energy in Eq. (B6) is identical to the expression that arises for a spinning top. But because our coordinate system has its origin at the center of mass while the standard treatment of a spinning top has its origin at the fixed point of contact, the two expressions, while functionally identical, will not give identical results. While we are embarrassed by this blunder, it in no way affects the results in our paper.

We thank William Case for bringing Ref. 2 to our attention.

1.
D. P.
Jackson
,
D.
Mertens
, and
B. J.
Pearson
, “
Hurricane Balls: A rigid-body-motion project for undergraduates
,”
Am. J. Phys.
83
(
11
),
959
968
(
2015
).
2.
W.
Case
, “
The gyroscope: An elementary discussion of a child's toy
,”
Am. J. Phys.
45
,
1107
1109
(
1977
).