Ain’t physics grand?

around lunchtime on Wednesday, the 9th of November 2005 by Chad

DROWNING IN QUICKSAND IS IMPOSSIBLE, according to a new study, relegating this popular plot device in adventure stories to the category of pure folklore. Consisting of a mixture of sand, salt water, and clay, quicksand captured the attention of University of Amsterdam physicist Daniel Bonn when he went on a family trip to Iran, the birthplace of his wife. Collecting a sample of quicksand near a body of water in Iran, and bringing it to his laboratory for study, Bonn and his colleagues showed that shaking aluminum beads, designed to have the same density as human beings, would partially, but never fully, submerge them. Since quicksand is twice as dense as water, the beads (and humans) only sink about halfway. Shaking or otherwise disturbing the quicksand liquefies it, increasing the downward flow of the beads by a factor of a million. This is how humans can get stuck in it. Since quicksand is often located near bodies of water, Bonn speculates that high tidal floods passing over individuals stuck in quicksand may have caused casualties incorrectly ascribed to sinking fully in it. Bonn says his conclusions apply to all kinds of quicksand. Nonetheless, the force required to lift a foot out of quicksand can be equal to that required to raise a car. His solution: wiggling the stuck foot will cause water to trickle down, allowing the hapless adventurer to get out of it. (Khaldoun et al., Nature, September 29, 2005)