# Physics Q. : Alec Baldwin, 'The Shadow', trapped in water tower, air bubbling IN?? **URL:** \ **Category:** Factual Questions\ **Created:** [February 5, 2001, 3:27am UTC](https://boards.straightdope.com/t/physics-q-alec-baldwin-the-shadow-trapped-in-water-tower-air-bubbling-in/53161 "2001-02-05T03:27:25Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![fierra](https://avatars.discourse-cdn.com/v4/letter/f/58956e/32.png) [@fierra](https://boards.straightdope.com/u/fierra)\ **Post date:** [February 6, 2001, 3:42pm UTC](https://boards.straightdope.com/t/physics-q-alec-baldwin-the-shadow-trapped-in-water-tower-air-bubbling-in/53161/21 "2001-02-06T15:42:51Z")
> [@](#): > > \*Originally posted by CalMeacham \* > **That’s why skorkels are so short, and why SCUBA divers have tanks of PRESSURIZED air on their backs.** That’s not why at all… Say you have a dive tank of 10 litres capacity. If the air in that tank were at atmospheric pressure (1 bar), it wouldn’t last very long…you would only have 10 litres of air to breathe…I don’t know if you ever did the school experiments to find your average lung capacity, but it’s about 1-2 litres, so you figure it out… The air in the tank ranges from 250-300 bar of pressure, so 300\*10 = 3000 litres of air to breathe. Of course it isn’t atmospheric air…it is put through scrubbers to remove moisture (moist air under pressure is very bad for the tank…especially the steel ones) & things like Carbon Monoxide which are bad enough at single pressure, let alone at greater partial pressure… The tank is equipped with a 2-stage regulator, which steps the air down in 2 jumps - first jump down to 10 atmospheres of pressure & then the last stage takes it down to 1 atmosphere (ie air pressure). The regulator has a demand valve & only provides air when there is a step down in pressure on the outside…occasionally this will jam and it freeflows, which is a quick way to die, unless you are diving in a pair. Oxygen in the levels found in atmospheric air becomes toxic at approximately 70-80 metres depth - I don’t have my charts & tables with me at work, but if you are interested, open a new thread, as I really didn’t mean to hijack this one so much - which is 1 atmosphere pressure for the air, then 1 atmosphere for each 10 metres of depth gained so 8-9 atmospheres of pressure & you would still be able to breathe at this depth. I’ll let other people fill you in about nitrox mixes/oxy-helium diving, as I haven’t used them myself. ---
**Author:** ![Spritle](https://avatars.discourse-cdn.com/v4/letter/s/5daacb/32.png) [@Spritle](https://boards.straightdope.com/u/Spritle)\ **Post date:** [February 6, 2001, 3:56pm UTC](https://boards.straightdope.com/t/physics-q-alec-baldwin-the-shadow-trapped-in-water-tower-air-bubbling-in/53161/22 "2001-02-06T15:56:22Z")
::Former physics teacher still in the room:: Let’s go back to the 2L bottle experiment. This is not entirely applicable here, since the movie has the tank filling up with water while the bottle experiment is draining the tank. With that in mind, lets look at the two possibilities (and sub-possibilities). 1. Tank is sealed at top. Water can be pumped into the tank. Water level will rise. Air space will decrease. Air can’t leave and space shrinks so air pressure in top of tank increases. This will continue until the air pressure in the top equals the pressure that the pump is pushing in water. Consider, lets say that the pump is pushing in water such that the surface of the water is being pushed up with a pressure of, say, 100 psi. When the air pressure is pushing down with 100 pounds per square inch (psi) on the surface of the water the tank will stop filling. Person trapped can breathe air trapped in top. Now, lets shoot the hole in the side of the tank. While the water is below the level of the hole, air escapes **out** through the hole. When the water level is above the hole, the above holds true except the water will be pushed **out** of the hole. As the pump pushes more water into the tank (at 100 psi.) and the air pushes water down (at 100 psi.) any water pumped into the tank will squirt out of the hole (pressure of water exiting hole is dependent on diameter of bullet hole). 2) Tank is open at top. By “open” we simply state that air at the top of the tank can escape while the tank fills. Without holes, the tank fills and air escapes. Some air may be trapped in top, depending on location of vent. Again, let’s shoot the hole in the tank. When water level is below bullet hole, we have the same situation as in solid tank: air escapes **out** hole and vent. When water level rises above bullet hole, things get a bit tricky. The problem stems from not knowing how quickly air can escape top vent. If top vent is a pin-hole (water comes in faster than air goes out), pressure builds up and pushes water out of the bullet hole. If the vent hole is very large, larger than the bullet hole, (air can go out as quickly as water comes in) water will dribble out of the bullet hole as tank fills, due to gravity, and water pressure associated with depth. Since air is allowed to enter/exit the top of the tank, air does not need to enter the bullet hole – **ever**. QED ---
**Author:** ![Spritle](https://avatars.discourse-cdn.com/v4/letter/s/5daacb/32.png) [@Spritle](https://boards.straightdope.com/u/Spritle)\ **Post date:** [February 6, 2001, 4:08pm UTC](https://boards.straightdope.com/t/physics-q-alec-baldwin-the-shadow-trapped-in-water-tower-air-bubbling-in/53161/23 "2001-02-06T16:08:15Z")
**Cal Meacham** , this thread has some interesting stuff regarding pressures, scuba and other such stuff. [http://boards.straightdope.com/sdmb/showthread.php?threadid=47504](http://boards.straightdope.com/sdmb/showthread.php?threadid=47504) ---
**Author:** ![LateComer](https://avatars.discourse-cdn.com/v4/letter/l/b5ac83/32.png) [@LateComer](https://boards.straightdope.com/u/LateComer)\ **Post date:** [February 6, 2001, 4:51pm UTC](https://boards.straightdope.com/t/physics-q-alec-baldwin-the-shadow-trapped-in-water-tower-air-bubbling-in/53161/24 "2001-02-06T16:51:40Z")
> [@](#): > > \*Originally posted by Rocketeer \* > **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.** Rocketeer is absolutely right (Was there any bogus physics in the Rocketeer movie? That was rhetorical). “Sealed” or not, the only way air would bubble into the bullet holes is if the holes let out air at a greater same rate than water was being pumped in. Otherwise, any displaced air would be quickly replaced by water. I would have to ask (and I know it’s a bogus scene) why wasn’t the water tower turned on to begin with? It should have water pumped into it at a constant rate. Zenbeam and anybody interested in how water towers work, check out [How Water Towers Work.](http://www.howstuffworks.com/water.htm) ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [February 6, 2001, 11:13pm UTC](https://boards.straightdope.com/t/physics-q-alec-baldwin-the-shadow-trapped-in-water-tower-air-bubbling-in/53161/25 "2001-02-06T23:13:47Z")
Well, it wasn’t clear from the movie that it even WAS a water tower. It was just this huge globular building at the end of the street, and it had hatches and valves and things, and Alec Baldwin and Tim Curry ran into it, and nobody said anything like, “Ah ha, I’ve got you trapped in the water tower now!” and after some initial scuffling, Tim Curry turned one of the hatches and water started flooding out, so one simply assumed that it was some sort of water tower. They started out with a dry floor; it wasn’t a “water tower full of water”. And it was the kind of movie where you don’t ask too many questions anyway. The opening scene was titled “In the Tibetan opium fields”. Um, I didn’t know Tibet was a center of opium production… Then, we get the bad guy, the “last living descendent of Genghis Khan” and his henchmen, in full Mongolian battle dress, being billed as “Tibetans” throughout the movie. Obviously the screenwriter had Mongolia and Tibet confused on the subject of Genghis Khan, although we never did figure out the “Tibet/opium” connection. So, yeah, it was kind of a bogus movie overall. [Previous page](https://boards.straightdope.com/t/physics-q-alec-baldwin-the-shadow-trapped-in-water-tower-air-bubbling-in/53161.md?page=1)