Physics Q. : Alec Baldwin, 'The Shadow', trapped in water tower, air bubbling IN??

I just wanna make sure I told my kid the right thing. We’re sitting here watching the Alec Baldwin version of The Shadow (1994?) and Tim Curry has Alec trapped in the water tower, and he shoots off a gun a few times, and manages to slide out and lock Alec in, but not before turning on the water. So the water tower is filling up with water and Alec is trapped inside. And the water is rising steadily and then it’s all the way up to the top and there’s no air left, so Alec goes over to where the two or three bullet holes are, in the side of the water tower, and here’s the thing–there’s air bubbling INTO the water tower, instead of water squirting OUT. So he puts his mouth on the air bubbles and gets enough air to survive the next 20 seconds or so of screen time until Penelope Ann Miller gets there and lets him out.

So I look over at Bonzo and I go, “Huh?” And he says, “What?” And I say, “Well, the air shouldn’t be bubbling IN, the water should be squirting OUT.” He says, “Oh.”

So I wanna make sure I told him the right thing. If you were inside the water tower, you wouldn’t see air bubbling in, right? It’s been bugging me all afternoon.

Yes, indeedy. As the water pressure builds up the water pours ut. Another thing that water pressure does is to keep you from breathing in – even if you have an air hole. As kid, I took a hose with me into the pool to let me breathe underwater (the end was outside, f course, and I made sure there was no water in the hose). You can only go down a foot or so before you can;'t expand your chst against the water pressure. That’s why skorkels are so short, and why SCUBA divers have tanks of PRESSURIZED air on their backs. So The Shadow wouldn’t have made it. Unless he used some of those hindu fakir tricks for holding his breath.

I don’t really see the problem. Water would flow out, and air would bubble in to fill the space that was previously occupied by the water. It’s not like the water is going to expand to fill that space. If no air bubbles in, no water is going to flow out. Similar reasoning to why you punch 2 holes in a can of Hi-C punch.

That is correct.

The atmospheric pressure at the top of the tower is the same both directly above the tower and off to the side. The pressure inside the tower equals the atmospheric pressure at the top plus the pressure due to the column of the water. Outside the tower the pressure equals the atmospheric pressure at the top plus the column of air. Since water is denser than air the pressure inside will be greater than the pressure outside and water will be forced out the hole.

However if the tower is perfectly sealed then air must chaotically enter the hole so the departing water does not create a vacuum, but I assume that is not the case.

::Former chemistry/physics teacher enters the room::

If the top of the tower is perfectly sealed, the increase of water in the tank will increase the pressure of the air above it; this air can’t get out and its volume is being reduced. This is a simple application of Boyle’s Law. This is basically how the water tank in your crawl space works (for those of you with local pump and not city water).

Of course, the location of the bullet holes will affect this - if they are above or below the water line. In any instance, I can’t see a person surviving by “breathing” through one of these holes.

Just wanted to point out that, in the movie, the top of the water tower was sealed. It had to be. If it was not, then Alec could have simply headed up to the surface to breathe.

BTW, how did he manage to stay near the holes as opposed to floating away? Even clothed, he is positively buoyant. That’s why SCUBA divers wear weight-belts.

Or was there a handhold that just “happened” to be located nearby?

If the tower was sealed, then why couldn’t he breath the pressurised air that would be trapped at the top of the tower? Also if the tower was sealed then I would have thought no air bubble would enter the bullet holes, as the lost water, would be replaced by water from a higher level, the water level in the tower drop, with the air above expanding, its pressure returning somewhat back to its initial level.

I was under the impression that the length of a snorkel was more to do with lung capacity, than pressure. With too long a snorkel causing asphyxiation by the build-up of exhaled CO2, not positive though.

I would guess that the water tower would have vents to allow air to escape as the tank was being filled, thus preventing a pocket of high pressure air building up. There still wouldn’t be air bubbling in through the bullet holes, though.

Ha! I get to apply knowledge gained from one of those dumb Two-Minute Mystery books!

To recap the story- Bob the Cowboy was being chased by a posse for a crime he didn’t commit. Jack the Doctor agreed to hide him, and gave him a length of bamboo six feet long, about the size of a quarter in diameter, and told him to hide in the creek until the posse went by. Afterwards, Bob was found dead in the creek. What Happened?

Supposedly, due to lung capacity, he couldn’t inhale enough to get fresh O2 through the tube. Sounds plausible enough.

This site says that the average lung capacity of a human adult is 4.5 liters (8.4 pints).

Some napkin-mathematics … a six foot tube, two inches in diameter, would have about 226 cubic inches. 4.5 liters of lung capacity is about 274 cubic inches. So, breathing through such a tube would get you 48 cubic inches of fresh air, or only 17.5% of your regular lung capacity.

Of course, widen the tube to 2.5" diameter and you get 353 cubic inches, which would make it impossible to breathe through.

What a schlemiel. Put the tube in your mouth, breathe in through your mouth and out through your nose and you’ll have no problem with CO[sub]2[/sub] buildup in the snorkel.

Okay, in the movie they showed him fumbling around in the water which was all the way up to the top; there were hatches or something at the top, which presumably weren’t hermetically sealed, just closed. But he was definitely under water, and the whole water tank was supposed to be filled with water. And he swam down to where the air was coming in through the bullet holes.

It seems counter-intuitive to say, “The water was squirting out AND the air was bubbling in at the same time.” When you fill a bucket with water and hold it up and discover it’s got a hole in it, you just see water squirting out. You don’t see air bubbling in, too.

I’m still not seeing whether I’ve got a yes or no answer here. (It’s the part about Boyle’s Law that threw me.) Was the movie hilariously wrong? Or not? CalMeacham says he couldn’t have expanded his lungs to breathe at that depth anyway? I didn’t even notice that, I’m not a scuba diver.

Of course not… a bucket is not sealed. The air replacing the displaced water is coming in from the top of the bucket, so there’s no need for air to come in from the holes themselves.

Think about it THIS way:

You have a 2-litre bottle of (insert name of favorite soft drink here), which has a cap.
Turn bottle upside-down.
Open bottle.

While your kitchen floor becomes flooded (and eventually sticky) from your favorite soft drink splattering on it, you’ll see that air is fighting its way in from the same (and only) opening. The splattering effect is coming from the constant battle the Fanta/Sprite/Pepsi trying to follow gravity and make its way out the bottle is having with the air trying to make its way into the bottle to make up for the displaced liquid you are now christening your floors with.


After trying the soda bottle expierment do this with a zipper baggie. Fill the baggie full of water and zip it closed. Let Bonzo poke some holes in the baggie with a pin. Observe what happens and have Bonzo explain the difference between the baggie and the soda bottle.

(but I’d do it over the sink)

Ok now guys (and gals) this is just a movie (and a crappy one at that, no need to assume that the director thought about science when he/she was directing. If they were so concerned about science, they wouldn’t allow a man to disapear into a shadow, now would they?

Hmmm…Slight hijacking question:

I’ve never heard the “you can’t breathe in past a certain point down in the water” thing before. I was always irritated at the length of snorkels (on my many deep sea diving missions exploring the unknown depths of my bathtub when I was a kid), and just figured they were designed stupidly, heh.

I’ve heard that ninjas (back in the ninja days when they’d use the hollow reed trick) would carry bags (made of skin or whatever) full of air…Then they could go into the water (I imagine with weights to keep them down, since the bag would try to float up) and swim around…when they couldn’t hold their breath any longer, they’d blow out what was left in their lungs, and then put their mouth to the bag and suck in some air from inside it, and all would be well again…

Is this, then, completely impossible? Or only if you’re near the surface?

As for the Shadow thing…like others said, it would probably depend on where the bullet holes were…I’d imagine that you’d get a lot of water in your lungs as well as air bubbles if you tried to breathe in from the same type of situation as a pop bottle chugging it’s contents out.

I guess the answer is…who knows?

…The SHADOW knows, muwahahahahahahahahaa…

Come on, someone had to do it.

  • Tsugumo

OK, I did an experiment with a plastic 2 liter Coke bottle. I filled the bottle with water, then cut two small holes near the top, one 2 - 3 cm above the other (Note to self: next time, cut the holes first). The holes were about 5 mm in diameter. After refilling the water which spilled out, I put the cap on, and turned the bottle upside down, so the holes were near the bottom. Result: water poured out the lower hole, and air bubbled in the upper hole.

Next, I cut a small (1 - 2 mm) near the bottom of the bottle, refilled it while plugging all three holes with my fingers, and had Mrs. ZenBeam replace the cap. Turning the bottle upside down and releasing my fingers from all the holes, water flowed out both the lower holes, and air came in the upper hole.

So the result depends on whether the water tower is air tight near the top. I doubt very much they are, since it’s the weight of the water which provides the pressure in your water supply. Anybody here know about water towers? I imagine they must have some kind of system relieve the pressure as the water tank level rises and falls, but I don’t know what. You wouldn’t just want an open pipe, because pollutants and bugs could get in.

<apply Occam’s Razor>
It’s just that simple. Water towers (properly known as Standpipes) do indeed let air in and out through vents on top.</apply Occam’s Razor>

Hopefully they’re screened to keep the beasties and insects out. Not always. :wink:

As you assumed, they have to allow air in and out as the level of water increases and decreases.

Gravity and Simplicity is all there is to it.

  • A pal’s cajun-hillbilly grandfather who used to do the hiding underwater trick told me that it works good, but you only go under water about 18 inches because it’s so hard to inhale against the water pressure. Usually that’s all it takes though, because the water is usually green/brown enough that people above won’t see your head. He said he would find a good reed first, and then pick up a big rock and walk into the water carrying the rock, staying near a group of reeds.
  • Tsugumo: the ninja-airbag trick would work, because the air pressure in your lungs and in the airbag would be equal to the water pressure of whatever depth you were at. Both would compress with depth though, so you’d want to stick to the shallows. The problem with just inhaling through a long hose to the surface is that if you go down deep enough that (let’s say, to make things easy) there’s 30 lbs/ of water pressure, and the hose leads up to the surface that’s at 15 lbs/ of pressure, then you’ve got to inhale with at least 15 lbs/ of pressure to get any air at all. I don’t know how hard humans can inhale, but I suspect not all that hard. Certainly not nearly as hard as they can exhale, and I would bet anybody would struggle to produce 15 lbs/ by lung power if they could do it at all. SCUBA tank regulators are set up to always deliver air at just a tiny bit less than local pressure, no matter what depth they’re at (for the range of their useful depth). ~ If you [that is, anybody] has access to a hose and a suitable body of water, you could do this experiment in jut a few feet of water and report back how it goes. It likely isn’t gonna kill ya if it don’t work—just hold on to something heavy, don’t tie it around your waist. - MC

Easy: the movie is bogus.

We know that if the tank is sealed at the top, bubbles will come in the holes lower down on the tank, but not if the tank isn’t sealed at the top (according to logic and others’ experiments above).

So the question of whether or not the movie makes sense comes down to: was the tank sealed at the top? The answer to that is obviously no. Why? Assume normal operation with no bullet holes. If the tank is sealed at the top, how can it be filled? Where would the displaced air go? Clearly no real water tank would be designed this way.

But, you say…entertain the idea that this wasn’t actually a functional water tank, and that it just happened to be set up just so (perhaps by the bad guy as a death trap), sealed at the top. The bad guy knew that the sealed tank could not be filled since there was no way for the pressure to escape, so just before trapping our hero, he shoots some holes in it! If this were the case, air bubbles would indeed come into the upper hole as water poured out the lower one. However, our hero would be stupid to try to breathe from these, since in a sealed tank, there would be a large volume of air trapped at the top.

Only the shadow knows? Puhleeze. :slight_smile: Conclusion: bad movie physics.

The scene is BS. The water coming into the tank is still turned on, so effectively the tank isn’t sealed; any water gushing out the bullet holes would be replaced by water from the city mains. The tank is effectively at city water pressure. Ergo, no air would bubble in.

Incidentally, I liked the movie, except for the completely unnecessary scene at the start in the opium fields. No reason that info couldn’t have been done in flashback. One of the reviews I read called it a “poor storytelling choice”. Absolutely right.

First scene in the movie should have been the bridge scene with the Chinese physicist.