At a historic Civil War battleground, a stack of cannonballs looked like the picture below on the far left. Removing the top cannonball resulted in the middle view, and removing the next layer resulted in the view on the right. What sort of packing was used in stacking the cannonballs?
A) cannonball closest-packed
B) hexagonal closest-packed
C) cubic closest-packed
D) random-packed
E) body-centered closest-packed

Question

At a historic Civil War battleground, a stack of cannonballs looked like the picture below on the far left. Removing the top cannonball resulted in the middle view, and removing the next layer resulted in the view on the right. What sort of packing was used in stacking the cannonballs? 
A) cannonball closest-packed 
B) hexagonal closest-packed 
C) cubic closest-packed 
D) random-packed 
E) body-centered closest-packed

Quizplus · Accepted Answer

The pattern of stacking seen in the three views is consistent with a cubic closest-packed arrangement. In this arrangement, the bottom layer consists of a square arrangement of cannonballs, the second layer is shifted by half a ball diameter to create the square arrangement with each ball in the bottom layer, and the third layer is shifted again. This pattern repeats to create a cubic closest-packed arrangement.

At a Historic Civil War Battleground, a Stack of Cannonballs