Quick, Sand!

by chelsea schuyler

So the other day I was replaying The Princess Bride film in its entirety in my head, as per my civic duty, and I got to the part where Robin Wright is sucked instantly down into a pit of quicksand. Our hero Cary Elwes grabs a vine and dives in, and for a moment of suspense both are completely submerged. …BUT then his arm thrusts out of the sand and he pulls her out with Herculean strength up the vine and all is well.

Pausing my filmstrip at this point, I asked myself – could that really happen? Dear God, what IS that thing we call quicksand? Kitu and I decided to investigate. Turns out there’s three ways this movie incorrectly portrays death by sand:

#1 In the movie, the sand is completely dry and it falls off their faces like beach sand. In For Real, quicksand is made of, yes, sand, but the whole essence of it is water. If you take a bucket half filled with loose sand, you could stand on it. Ground is solid because of friction, the friction of the various grains holding each other in place which in turn supports weight. Seen here.


Kitu is secure in his elevation


An unsuspecting passerby is unharmed











If you poured water into the rest of the half and agitated the mixture so it is totally homogenized, the water will lubricate the particles and they loose their friction. Seen here.

Kitu is wisely skeptical

In quicksand, there must be an underground water source. Flowing water from below is pushed upwards, agitating and liquifying the sand above. The particles are forcibly separated and not only can’t support weight, but anything pulled out of it creates a vacuum from below.

Pulling your foot from quicksand at one centimeter per second requires the same amount of force you would need TO LIFT A CAR. (#2 thing wrong in Princess Bride, you would dislocate your shoulders before getting out that fast.  Never tie someone to a truck to pull them out of quicksand, you would rip their body in half—i know, almost still worth it)

The thing is, quicksand is a non-Newtonian fluid, which is a fluid that openly hates Newton and all he stood for and so defies the way fluids, by his definition, are suppose to act. Patriotic, God-fearing Newtonian fluids don’t act differently when pressure is applied. Water for example, will flow the same way whether you slowly dip your finger in it or slap it. Anarchist, non-Newtonian bitch fluids change their viscosity (measure of resistance, “thickness” basically) when pressure is applied. Slowly dip

Ublick does not condone hammertime

your finger in and it will act like thick water and let you. Slap it, and it will act like a solid and you will break your hand.

Ever made oobleck at camp? Half corn starch, half water, = a liquid if you’re gentle, a solid if you push. If you made a pool of oobleck (which I want for my birthday) you could run across it, but if you just stood in it, you would sink (though you’d float eventually, bein’ all less dense n stuff). Quicksand is like a really heavy oobleck, only sucking you from below.

panic is not advised

So it is hopeless? No. First of all, it’s very rare for quicksand to be very deep. Usually not beyond your knees. But even if it is, the key is not to focus on the lifting a car thing, but the centimeter per second thing. Go SLOWLY, remember, solid if you’re fast, liquid if you’re slow. First of all, don’t panic, panic makes you flail and that just helps the vacuum. Have faith in physics, technically you can’t sink all the way under, you’re half as dense (#3 thing wrong in Princess Bride, you can’t get sucked in all the way, and never instantaneously)  (though if you’re not buoyant, kiss this world goodbye, like the 1878 train that crashed into quicksand in Kansas, the engine was never found again!!)

Try to move slowly to reduce viscosity, change the angle, making yourself more horizontal and closer to the surface. Here’s that guy on Man vs Wild demonstrating for us.

So even though you now have a sort of Up Up Down Down Left Right Left Right B A Start to escaping quicksand, that doesn’t make it less deadly. So let me reintroduce the reason you might choose to panic in such a situation.

Quicksand won’t suck you under, but it can keep you there, exhausted and stuck. Unless there’s a rising tide (Alaska, 1988), it’s unlikely that you will drown, it’s exposure that kills people. Which is the most uneventful death ever and therefore probably the most frighteningly lonely and defeating. The sun, the cold, or thirst whittles away at you. Or you’re mauled by animals! Which would instantly put you in the cool group of the afterlife.

So, it’s still awesome, just not in the old fashioned wrong ways.  In the 1960s, quicksand was shown in 3% of movies. Unfortunately, poaching and loss of habitat has pushed this brilliant adventure gimmick to the brink of extinction (0.5%).  Donations welcome.

But please, step carefully.



    • Thanks Teejay! I rarely get to act out and demonstrate with scientific objects like buckets and cats, so this one was a treat. Let me know if you’ve got a good science question you’d like explained wittily and informatively!


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