# Which is more efficient in stopping a bullet, small cubes or fine grains of sand

Recently, I was presented with the following problem, relating to pressure: which would be more efficient in stopping a bullet, small cubes or fine grains of sand.

Using my intuition, I would say the small cubes, since it has a larger surface area as compared to the fine grains of sand, and would likely have a strong structural integrity that is difficult for the bullet to penetrate. I tested this out by punching my Ricola candies (cuboid shaped) as opposed to the sand on the beach, and I discovered that my hypothesis was correct to a certain extent, since it was much more painful punching the candies.

I could not therefore understand why in the war, sandbags are used to block bullets? My teacher also disagreed with me by raising the fact that sand is highly compact and it is thus very hard for a bullet to penetrate. I would like to ask, is my idea correct?

• There are many variables that you have not controlled in the experiment that you have performed so far, but even if you are right, how much will it cost to fill bags with enough "small cubes" to stop a bullet, as opposed to filling them with enough sand? en.wikipedia.org/wiki/Hesco_bastion – Solomon Slow Aug 23 '18 at 12:42