A rattleback is a type of spinning top that prefers to spin in one direction due to its unique semi-ellipsoidal shape.

How it works:

When spun in the wrong direction, it will automatically shift momentum until it spins in the opposite direction. This is caused by an asymmetric mass distribution and the instability between the rotational axes. As the mass shifts, the rolling axis compensates in the other direction, which in turn causes the mass to shift more.

This continues until the top is spinning in the preferred direction. But when spun in the “right” direction, the mass needs no compensation.

Challenge a know-it-all to explain the physics behind these simple shapes.

Dimensions: 3 ⅞" x ¾" x ½"