This was inspired by another recent thread about falling from height into water.
My question is, could you survive by attaching a collapsible rod to your feet with a sodium capsule at the end?
My thinking is that the capsule would hit the water a little bit before you, and react with the water creating a small explosion that would break up the surface tension for a second or two, allowing you to survive hitting the water.
Would this work?
So now, instead of landing in water, you’re landing amidst a small explosion.
And this seems like a better idea?
I think it would have to be a lot bigger than a capsule. I’m not familiar with sodium’s reaction to water but if you were looking to just break the surface tension for a split-second, I think you’d need to start sooner than an inch before hitting the water, though. (Don’t forget you are going over a 100 miles/hr!)
Maybe if the sodium log was toothpick-shaped and your feet were tied to the thicker side, and you shot right through the water… that might work. I don’t know how long the sodium shaft would have to be… probably pretty long since your terminal velocity would be astronomical due to the aerodynamic shape. You’d probably want some fins too to make sure you head straight down and don’t flip over or something on the way down…
I definetely think somebody should try this, though. Seems like a good idea.
No not me.
Well, we’re not talking nuclear bombs here. I’m not sure how energetic an explosion would be necessary to disrupt the surface tension in water, but my wild-ass guess is that making the water “fizz” may be enough.
Anyone care to take a stab at this (related) question?
As far as timing goes, when you through sodium into water, it seems to start reacting instantly. If we assume that 1/10 of a second is necessary, this works out to 15-20 feet.
Is this realistic?
Perhaps a better approach would be to attach the sodium capsule to a cord, which is attached to your feet. The capsule could be shaped such that its terminal velocity is a little greater than a man’s, so it’s always falling “ahead” of you.
The cord could be made 50 feet long, so the capsule hits the water a good 1/2 second ahead of you. You could make it so the cord winds into the capsule and you “release” it once you’ve fallen clear of . . . whatever it is you’re falling from.
Folks, the problem is probably not the surface tension of the water. I expect you have more to worry about from inertial effects. Water is a fairly dense substance, at least compared to air. When you hit the water, it has to get out of your way to let you through. Since water doesn’t compress worth a damn, it has to literally MOVE out of your way. The force needed to move an appropriate volume of water quickly (at 100 mph terminal velocity,that is very quickly indeed) out of the way has to be exerted by your body. It is this force that is going to hurt you.
Expressed another way, your terminal velocity in water is much lower than your terminal velocity in air. Your body would have to deal with the sudden and extreme deceleration from the terminal velocity in air to the terminal velocity in water.
Oh, by the way. Trust me. You do not want to be in the area of a chunk of sodium in water. The stuff BURNS in water. Imagine white phosphorus, but worse, and shiver.
Folks, the problem is probably not the surface tension of the water. I expect you have more to worry about from inertial effects. Water is a fairly dense substance, at least compared to air. When you hit the water, it has to get out of your way to let you through. Since water doesn’t compress worth a damn, it has to literally MOVE out of your way. The force needed to move an appropriate volume of water quickly (at 100 mph terminal velocity,that is very quickly indeed) out of the way has to be exerted by your body. It is this force that is going to hurt you.
Expressed another way, your terminal velocity in water is much lower than your terminal velocity in air. Your body would have to deal with the sudden and extreme deceleration from the terminal velocity in air to the terminal velocity in water.
Oh, by the way. Trust me. You do not want to be in the area of a chunk of sodium in water. The stuff BURNS in water. Imagine white phosphorus, but worse, and shiver.
Looks like Mort beat me to it.
Since the force required to move the water out of your way is so high , hitting water at terminal velocity is roughly like hitting concrete. The effect on you is about the same.
Hitting foam (or “fizz”) may be a little better. Foam is mostly compressable air bubbles. The problem is that you need to make that foam thick enough to slow you from around 200 mph to a more survivable 20-30 mph. I’m guessing at least 50 feet think or more. A little stick of sodium just wouldn’t cut it.
::Former Chemistry/Physics teacher enters the discussion::
I won’t go into the idea of why Sodium won’t work; the above posts did a beautiful job.
However, a couple of points must be made.
The oxidation of sodium take place around 10[sup]-14[/sup] seconds.
While sodium is cool when reacting with water, it’s a wussy reaction when compared to other, larger alkali metals. (Cesium is much more violent.)
Sodium doesn’t burn (in the ‘traditional’ sense[sup]*[/sup]) in water. It oxidizes according to the following reaction:
2Na + 2H[sub]2[/sub]O --> 2NaOH + H[sub]2[/sub] + nrg
Now, quite a bit of energy is released, and it’s released in a short amount of time. This energy can cause the Hydrogen gas to reach it’s flash point and combust.
[sup]*[/sup]To those of you who think that burning is just rapid oxidation, you are correct. However, we tend to classify rapid oxidation into classes, one of which is rapid oxidation of hydrcarbon/organic molecules. These reactions produce water and various carbon-oxide compounds. These are what we “traditionally” call burning.
It is not. Check out some threads from the archives.
Why so many fatalities from jumping off bridges? - brad_d has some excellent posts in this thread.
Practical (not particle) Physics
The discerning reader might notice that this topic is a particular pet peeve of mine.
What’s been said so far pretty much sums it up. I just want to note that I’ve worked with alali metals quite a bit. You o NOT ant to screw around with this stuff if you don’t have to – the alkali metal - water reaction generates hydrogen gas and heat. The heat ignites the hydrogen, which burns with a pretty, colored flame. But in practice a lot mre happens. The lump of metal – which has really low density, so it floats – gets lifted up on the plume of gas and goes skittering across the surface of the ater. The heat generaed can actually melt the alkali metal, so that you end up with a blob of molten metal rather than a sold bt skittering across the waterm flaming all the way. This stuff can get into your eyes or mouth, or can get onto your skin and stick there. If you want a reaction, strap Fizzies onto your feet, not alkali metals like sodium, potassium, rubidium, or cesium (or Francium – but that stuff adds radioactivity to its problems. Fortunately, it’s extremely short-lived).
If you want to break the surface tension and overcome the sudden resistance of going into the dense medium of ater, let me suggest something that I saw in an old Batman comic strip – he and Robin tied large rocks to their feet and rolled thes off the cliff, into the water far below. The rocks broke through the surface and carried them along. Once in the water, the Dynamic Duo remained conscious and had the presence of mind to cut the ropes with their knives. Batman noted that Hollywood stunt-men did the same thing, only with a device that automatically released after you hit the water (in place of the rock). I don’t know if it’s true, but it souns plausible. I still wouldn’t do it – not without a lot of experimentation, a support team, and a good insurance policy.