question

[woolymonkey]

Squirrelmonkey has lots of questions. This is today's.

How big/heavy would a sponge have to be to crush a person? Is it physically possible?

He knows sponges don't grow that big. He's wondering about mass and gravity and squidgeyness.

Thoughts, anyone? Please?

Comments

[http://users.livejournal.com/la_marquise_de_/]

My feeling is that any sponge sufficiently large would suffocate the victim before it crushed them. But I'm a historian.
The marquis says: first of all, we require an environment from which the deformability of the sponge can be excluded, because otherwise the sponge could well bend down either side of the victim and end up with most of its weight not on them. So start by putting your person in a narrow vertical tube. Then grow/load the sponge in the top part of the tube. Now estimate the density of the sponge. Assuming that the average dry bath sponge weights 10g, a metric tonne is sufficient (more than! Kari) to crush a person, so we then look at the volume of the sponge -- say half a litre, so a cubic metre of sponge weighs 20kg. Thus we need 50 cubic metres of sponge to weigh a tonne. Therefore -- 50 cubic metres of sponge is required. Clearly these numbers need to be refined by more accurate estimates of the density of the sponge and the weight required to crush a person -- this is left as an exercise for the reader. Deformability of a sponge is clearly going to increase the amount required, and for a free-ranging sponge the question becomes what pressure is required to deform a sponge by the height of the person (hence suffocation before crushing, Kari).

[veronica-rich.livejournal.com]

I'm not as up on my mass vs. area as I should be, but then again, this is a good thing for Squirrelly to go look up. I seem to remember some relationship that says if a thing doubles in size, it quadruples in weight or mass.

Of course, then comes the question: dry or saturated?

[woolymonkey.livejournal.com]

Thank you both!

Squirrel is now wondering: what if you had an oxygen pack?

[woolymonkey.livejournal.com]

He says it's dry. Not sure how he knows that...

[woolymonkey.livejournal.com]

The more I think about this, the more I become concerned that the sponge is going to stick in the tube, due to friction, and possibly expansion pressure. This would, of course, interfere with its crushing abilities. Or the tube might break before person-crushing force was attained.

Or is this one of the infinitely strong, infinitely friction-free tubes stocked by good maths depts everywhere?

[http://users.livejournal.com/la_marquise_de_/]

The marquis informs me that both tube and sponge are frictionless.
And the oxygen pack would, of course, protect from suffocation but not from the crushing.