Suppose a person has a very long straw oriented vertically, with its bottom end submerged in a bucket of water. The person puts their mouth on the top end and produces a vacuum in the straw using their chest/diaphragm (not their tongue/jaw). This causes the water in the straw to rise up above the level of the water in the bucket. How high up would a person be able to pull that water?
Another way to ask the same question:
If a person submerges in a pool with a pipe from their mouth the surface of the pool, how far can they descend and still be able to inhale any air?
FWIW, I tried this in a hot tub with some scrap copper pipe from my dad’s junk collection. It was very difficult to inhale with my chest at the bottom of the hot tub (so 2 feet below the surface), but I was able to do it. I wonder how much deeper I (or any random/average person) could go and still just manage to inhale.
We did this question many years ago. My method, which some people thought was cheating was to suck in as much as possible, close off my mouth with my tongue then suck again. I got it over 8 feet. My wall still has the mark I made.
We had a discussion about this on this board in 2006.
What I’ve always heard is the limit at which a person’s diaphragm can overcome water pressure is about 2-3 feet. I can’t immediately find an authoritative source for this, but various discussions on the Interwebs agree with this number.
This website suggests that some ‘students’ could suck water up a pipe to about 7 metres.
http://newsletter.oapt.ca/files/how-strong-a-vacuum-can-you-make.html
That is somewhat vague, unfortunately. There are a lot of factors that might increase or decrease the height to which someone can lift water by this method, and I find the 7 metre height (nearly 23 feet) somewhat dubious.
Looking at the pictures in that article, the column of liquid seems to be broken, so this may not represent an accurate reading.
Doesn’t this depend on how small the cross section of the straw is, the density of the liquid and the atmospheric pressure?
My thinking: vacuums don’t suck, it is the atmosphere pushing on the liquid in the glass/bucket that causes the liquid to go up the straw. If you expel as much air as you can from your mouth and lungs, then as you ‘suck’ up the liquid it is pushed up by the difference in pressure between your mouth/lungs and the atmosphere. But it can only go into the space that is available in your mouth (assuming you’re not going to choke and let it into your lungs). So the thinner the straw, the less liquid per length, so you can suck more up, before it runs out of space in your mouth? And even then, there is a limit as to how high the liquid can go, depending on atmospheric pressure and the density of the liquid.
Or am I way off here?
Another problem is that a very strong vacuum can cause the liquid to boil, and that provides an upper limit on the height of the column.
However a very thin tube can raise liquid by capillary action as well.
When I was a kid I carefully emptied a garden hose so that I was sure it was completely empty, then took it into our swimming pool and tried to inhale at the bottom. Our pool was four feet deep, and I couldn’t even begin to do it. I could inhale, with difficulty, at about the 2 foot mark, so my experience agrees with yours.
This is why scuba divers use compressed air and regulators. A year or so later my scuba-diving cousin brought hs rig to our pool, and I had no problem breathing on the bottom with his equipment.
Yep. For atmospheric pressure, the highest column of water you can draw up (by pulling a vacuum on the free surface of the water inside the straw) is about 32 feet. Based on my experience and @markn_1’s post, someone inhaling on a straw (or through a long snorkel) can only manage 2-3 feet of water, so no way we’re hitting 32 feet.
You’re exactly right on the technical details, but those technical details are exactly what people mean when they say they are sucking liquid up/through a straw.
My assumption (in the OP) is that the straw is so long that the person can’t possibly pull the liquid column all the way up to their mouth, because they can’t pull a strong enough vacuum to get it all the way there. So the available space in one’s mouth doesn’t matter, which in turn means the diameter of the straw doesn’t matter (provided it’s large enough so that capillary action isn’t a factor, and small enough so that the max volume of the lungs isn’t what’s limiting the column height).
All I’m really wondering is how strong a vacuum a person can pull using their chest and diaphragm muscles.
Tried some experiments with a tube.
Using my mouth as a pump, I could easily pull water up 8 feet (the longest tube I had handy). I could have gone farther with a longer tube.
Using just my lungs/diaphragm, I could get about 3 feet. The limit here was whatever my body did to close off my nose–air pushed through there at my limit, making a kinda phlegm-clearing sound.
If I manually pinched off my nose, I could get close to 5 feet. At this point, my sinuses were leaking and my ears popped afterward.
Possibly I could hit 8 feet with some practice, but I really don’t feel like pulling a muscle there.
I love people who do things like this. It makes me feel normal.
The other people are the weird ones. Why go on and on speculating about an experiment you can perform yourself in 5 minutes?
I have some longer tubes but they’re a lot more stiff and hard to unroll. Maybe I can clamp it to the leg of a chair or something. I know I can beat 8 feet but I’m not sure by how much.
Another anecdote: I learned about this principle when I was a kid at the beach. I enjoyed snorkeling and had a couple different brands of snorkel available.
Idle fidgeting with them showed that the end of one could be fit snugly into the other, giving me a snorkel a little under 3 feet long. Cool !
I submerged for a view of the bottom a little deeper down and got a good scare when suddenly I couldn’t breathe.
Further experimentation showed I actually could breathe, but only barely and with difficulty. Long snorkels are not much fun.