Ghost Of Lectricity

I’ve been pondering this question for some time:
When a person falls from a height into water, the bodily harm they receive is mostly due to the high surface tension of the water creating an almost solid surface. I wonder what would happen if a person fell from the same height into a substance without hydrogen bonding such as hexane which is held together as a liquid near room temperature by Van der Waals forces. Neglecting the obvious ulterior problems of being immersed in hexane, would a person receive less harm from falling into hexane vs water. Also if someone knows how to calculate and compare the forces of different surface tensions on a moving body that would be awesome.

Loren Pechtel

I don't think the surface tension is relevant on this scale. I think it's a matter of the mass that must be displaced to let you enter. That takes energy--you slow down very quickly. That's what hurts you.

Ghost Of Lectricity

If that's the case, wouldn't it be based on the density of the material?

Rhaedas

Certainly. Density is a measure of mass per unit volume. More mass, more density.

The fall through the less dense air isn't as damaging as the denser water, which would be more survivable than the more dense ground.

Air does impede motion...hence terminal velocity.

Loren Pechtel

Exactly.

Jack the Bodiless

It also helps if the substance is readily compressible, to absorb the impact energy: and liquids generally aren't.

There have been cases of people falling thousands of feet without parachutes and surviving after landing in a deep snowdrift. Snow has low density and is compressible.

Presumably, you could make a water impact survivable if you could inject a gas into the water and create a lower-density compressible foam of bubbles.

Ghost Of Lectricity

Interesting point. I was wondering what would happen if you fell into a gas compressed to the same density as water. I'd assume you could do this with helium because it doesn't really form a dimer unless it's under extreme conditions (I still feel that 55A of separation is too much to call anything a dimer). If things are based totally on density then the compressed helium should have the same resulting consequence as water, but if things are based more on material properties like Bodiless suggests then something quite different could happen. Though my guess is that there is a happy medium. Any idea on how to calculate this stuff?

Coragyps

You can warm carbon dioxide above 88 degrees F, its critical point, and then compress it enough to get a denser-than-water gas. They do just that to several thousand tons of it every day and pump it into the oilfield down below my chair.

But I don't volunteer to dive into any.

Loren Pechtel

I didn't realize it was denser than water.

They also use it for dry cleaning. It's more expensive but environmentally more friendly and leaves no hydrocarbon residue.

The whole thing is rather moot anyway, though--supercritical liquids are at pressures far beyond what the human body can survive suddenly entering.

Ghost Of Lectricity

Very true, but this is a thought experiment. Though I wouldn't object if anyone wanted to try it out...as long as it's not me.