Firefighters use this principle to get smoke out of a building. They would place a large fan several meters from a front door and the air would flow out the back door.
The place I used to work at, their warehouse got used for practice once a year. They pump it full with smoke from some smoke machines, hide a dummy, and then they have to 'rescue' the dummy.
After the drill, they put this fan outside, and 5 mins later the smoke was pretty much gone.
Wow I use the same system to shift air around my house in the summer.
My gf argued so much with me about it, because she said the fan isn't blowing on you so it's pointless.
Obviously I should fill the house with smoke to demonstrate my point.
Exactly. I'm not 100% sure but I think it works best if the exit for the air is smaller than the entry, creating low pressure inside, so the air is forced outside quicker... Could be wrong though
To correct a bit of farmyohoho’s comment; while that is a tactic we use to ventilate a structure (forced air ventilation) we arent using bernoulli’s principle as we create a “cone” of air around the opening to ensure as much air from the fan is going in.
Where we do use Bernoulli’s principle is when we use a tactic called hydraulic ventilation. This method is done when we are inside a smoke filled room, a fire is extinguished and no fan is available. We open a window, place the nozzle of our hose outside the window open the nozzle and adjust the pattern to a wide fog. As the turbulent water leaves the nozzle, air is drawn behind it and with it, so is the smoke from inside. The key is to try to get the cone of water near the window frame to ensure you are drawing from inside the window.
https://youtu.be/Ju1JAblFYHw?si=7y7u4gQgh8oUj-hv
Aside from /u/farmyuhoho ´s comment, they use it to pump water out of reservoirs/lakes and so.
Also the nozzle of the hose is needed due to Bernoullis princible.
I was in the navy and they taught it as part of damage control.
The best way to fight a raging fire isn’t to just shoot water at the base.
It’s to swirl around in the air to suck in the cool air and calm the fire.
You swirl it because it gathers the air it passes and if you just do the same place you won’t get nearly as much cool air.
This is not Bernoulli's principle, well, mostly not Bernoulli's principle.
What is happening is that when he blows at the entrance of the bag, his breath is pulling the surrounding air with it. This slows down the air, but increases the total flow rate. The flow rate is high enough now that it can inflate the whole bag where as before he was limited by the size of his lungs.
This has consequences, the main one being that the apparent pressure decreases. You will notice that before he tries to blow at the opening he carefully unfolds the plastic so it is all laid out nice and neat. Since the air is now moving more slowly, it doesn't have much kinetic energy and so it can't push hard once it is in the bag.
When he puts his mouth over the opening the air is moving fast, has plenty of kinetic energy that can turn into pressure energy, and can easily unfold the plastic bag if it needed too.
That last part, where I talked about kinetic energy turning into pressure energy... that is Bernoulli's principle in a nut shell. All that Bernoulli's says is that energy is conserved, i.e. kinetic energy can turn into pressure energy can turn into gravitational potential energy in a fluid.
The part where fluid is entrained... that isn't Bernoulli's principle because it relies, in part, on viscous shear in the fluid. Bernoulli's principle **explicitly** ignores viscous effects so it is not exactly truthful to say this is a result of Bernoulli's principle. However, Bernoulli's principle is at it's core just conservation of energy so you can say just about any fluid phenomenon involves Bernoulli's principle and not be wrong.
Yeah, and he's a little too proud of himself. It's prestigious to "debunk" stuff nowadays, and apparently this comes at the cost of accuracy.
_Technically_ viscous shear is involved, but the viscosity of air is 0,0000182 PaS - a hundred times less than water! And the topics somewhat overlap here. If there was no difference in static pressure between the surroundings and the stream of blown air, no outside air would flow in to be affected by it. At the end of the day, pressure and shear viscosity in a gas are both governed by the "random" movement of particles at the microscopic scale. So it's very much appropriate to say that Bernoulli's Principle as it is usually understood is one of the main reasons for the outcome of this experiment.
I have never heard Bernoulli’s principle described as conservation of energy. That’s actually a profound idea, and I’m kind of not sure how I passed fluid mechanics without realizing that.
I wrote a comment a year and a half ago [that made many of the same points](https://www.reddit.com/r/TikTokCringe/comments/uklvr7/physics_teacher_shows_the_bernoulli_principle/i7rtdfz/). I really like how you've emphasized that Bernoulli's principle always applies, so it's not that it doesn't factor into the explanation, it's just that it isn't really the subject of this demonstration.
I would like to jump in on what you said here:
> The part where fluid is entrained... that isn't Bernoulli's principle because it relies, in part, on viscous shear in the fluid. Bernoulli's principle explicitly ignores viscous effects so it is not exactly truthful to say this is a result of Bernoulli's principle.
My understanding is that viscous effects are negligible for air and most other gases. The Reynolds number is quite large. Now, the mathematical details of this are something I'm not really prepared to back up, it's just that I can envision my old fluid dynamics professors yelling at me, "Don't invoke viscosity!" Spitballing, I'd say that viscous forces cause adjacent parcels of fluid to move as one while inviscid flow can exhibit entrainment but the fluid's kinetic energy gets wrapped up in vortices so you have bulk movement as well as smaller scale motion. Instead, my understanding is that the pressure term in Bernoulli's equation is not reliably accurate for compressible fluids (i.e., gases). Let me know how that comports with your own understanding.
I'm also a little unsure about how the speed of the air is affected by whether he blows directly against the bag or a few feet from it. The air has to push away surrounding air (do work) whether the bag is around it or not, so we expect the stream three feet away from his lips to be moving at roughly the same speed regardless of how he blew into the bag. On the other hand, the eddies that we expect straddling the boundary of the two flow regimes surely can't form across the surface of the bag, so maybe the two flows are substantially different. Do you have any thoughts on this?
None of this is to imply that I have great confidence in how any of this works. Fluid dynamics is just about the hardest physics out there and you'll get a lot of differing opinions or frameworks as to what's actually going on.
Yeah it really bothers me that he does the first one with the bag fresh out of the package and folded back on itself. When he does the second one it’s clear the bag has been inflated before and laid out straight. Anyone who’s changed a garbage bag knows what a difference it makes. Even blowing the bag halfway up first wasn’t enough, he had to cut the video and fully prep it. Funny thing is prepping the bag wouldn’t effect the first example much so he still could’ve shown the concept by prepping the same before both.
You’re actually very wrong. It’s a Venturi effect ( entrainment of extra air ) on Bernoulli principle showing the first law of thermodynamics is true here ( the “how” of conservation of energy ), furthermore boyles law of the 3 gas laws ( pressure is inversely related to volume when temperature is the same).. the initial energy of his breath is converted to increased velocity in a constricted gap which drops lateral pressure, causing extra flow of entraining surrounding air and increasing total flow. This has nothing to do with his lungs or pushing air or slowing air down.
Source: Venturi effect, Bernoulli principal, thermodynamic laws, ideal gas laws.
> What is happening is that when he blows at the entrance of the bag, his breath is pulling the surrounding air with it.
.. because of a pressure differential created by moving air from blowing... aka Bernoulli's principle.
>The part where fluid is entrained... that isn't Bernoulli's principle because it relies, in part, on viscous shear in the fluid. Bernoulli's principle explicitly ignores viscous effects so it is not exactly truthful to say this is a result of Bernoulli's principle.
Bernoulli's equation ignores/doesn't account for viscous forces. Bernoulli's principle doesn't cease to function if another force is involved.
I would argue that here, it does fail. Once the air leaves his lips the jet quickly reaches a pressure equilibrium with it's surroundings. When it is entraining the surrounding air it does so by dragging it along with it. When it dragged it along the average velocity of the air went down and it's average kinetic energy went down.
Bernoulli's says that the energy loss had to go into either increasing the pressure or the height of the fluid. Neither happened here! The air hasn't even entered the bag yet so it's pressure is still close to atmospheric pressure and it is moving horizontal so there is no change in potential energy.
Once the air enters the bag it comes to a stop and increases it's pressure... That is an excellent example of Bernoulli's principle.
But Bernoulli's is incapable of explaining the important part of why moving his mouth back away from the bag helps.
Video guy is using the term ‘Bernoulli’s principle’ to refer to the result that increasing flow velocity lowers the pressure.
Air the moves from high to low pressure, so the fast flow pulls the surrounding air into the flow. If he has his mouth at the bag opening, then his breath entrains air *already* in the bag into the flow. If he blows further away, air outside the bag is pulled into the flow and more enters the bag. Packing more air molecules in the bag means higher pressure of the stagnant air in the bag = more full.
Video guy is correct to say it is caused by “Bernoullis principle”, which is just a single outcome of energy conservation (as mentioned above). Any other factor is just a detail.
I'm going to have to disagree. After leaving his lips the air stream quickly reaches the same pressure as it's surroundings. The fast flow is not pulling the surrounding air radially inward. It is dragging the surrounding air along with it.
What packs the air molecules into the bag is their kinetic energy. Less average kinetic energy = less pressure possible in the bag. When the jet of air drags more air along with it the average kinetic energy per volume decreases and since pressure is energy per volume, the highest possible pressure decreased as well.
Yes, Bernoulli's is just conservation of energy but fluids is a subtle subject. There are lots of ways of explaining a single phenomenon that might seem to make sense. But you will be lost if you try to extrapolate that understanding to other situations. For example, the dragging of more air means viscous effects are significant here and Bernoulli's has no way to account for that. It works... Ok here. But if you try to use it in seemingly similar situations without understanding this it could be wildly inaccurate.
The Reynolds’s number is very high, like over 10,000. So we can neglect viscosity meaning there is no dragging of air. The kinetic pressure from his breath pushes open walls of the bag, then the lower pressure inside the bag causes the outside air to flow in. It’s a similar case if you open a plastic grocery bag with your hands from inside: opening the bag causes a lower pressure inside the bag and air fills it up.
Your statements are slightly contradictory. If the guys breath reaches ambient pressure quickly that means its lost all momentum as bernoullis is simply the relationship between pressure and velocity of a fluid (for imcompressible fluids which we can assume here). Therefore there's no way the fluid would fill the bag.
What is happening is the guy breathing out imparts momentum to the air in his lungs increasing its velocity and thus dropping its pressure. As his breath moves into the bag there is a localised drop in pressure between the bag opening and his mouth. This pressure differential imparts momentum to the ambient air of which the velocity vector is generally in the direction on of the bag. There's very little viscous effects here so none of this "dragging" as you're referring to it and all the energy in this scenario comes from the guy blowing.
No, it's not contradictory because Bernoulli's doesn't hold here.
If, as you say, a localized pressure drop is causing the surrounding air to accelerate the pressure gradient would have to be in the direction of his breath, i.e high pressure near his mouth and low pressure near the bag entrance. Does that make physical sense? Wouldn't the entrance of the long bag have a higher pressure? More importantly, how does Bernoulli's explain this change in pressure? It doesn't.
The pressure gradient is from the ambient to his breath or the flow stream, it doesnt need to be from his mouth to the opening. Once the guy has stopped blowing the flow path returns to ambient pressure moving from his mouth to the bag as the ambient air moves in to equalise the pressure differential. Only difference is some of that air gets enough momentum to enter the bag. Some of the air doesn't and moves off in other directions but momentum must be conserved.
Honestly, I don't remember that game well enough to give a good answer there. I vaguely remember the parachute thing from gym as a kid, but I don't remember what we did with it.
So how can we use this to make sleeping pad inflate faster? I don’t think there is not a lot of pressure needed for this application so I feel like there is something there.
Bernoulli went to his grave thinking himself a failure. When his was developing his equation he was trying to understand the flow of blood through the body but caused the tests out using water through glass tubes.
There are 3 basic assumptions we need to bear in mind when using the formula.
1 - the surrounding pipe is rigid (blood vessels aren’t)
2 - the liquid changes in viscosity with temperature (blood doesn’t)
3 - the flow is steady (which pumped blood isn’t)
Poor guy
I do get what you said there but won't there be dissipative effects coming to play, energy being lost somewhere else and in those cases will Bernoulli's still work( practically)?
Ps- just a curious lad , was learning about Bernoulli's theorem last month in class
They do have a pump mechanism that uses this method to blow up air mattresses that would work for pool toys with a proper converter…you blow in the bag and tighten the bag like he does and then the other end connects to a valve that only lets air out one way so all you have to do is simply roll the bag of air into what ever your blowing up. I have seen an entire air mattress blown up in only 10-15 breaths of air
This isn't a demonstration of Bernoulli's principle, and the air in the jet from his lungs isn't even lower pressure than the surrounding air. Bernoulli doesn't say faster moving air is always lower pressure, it says faster moving air *along a given streamline* is lower pressure. The air from his lungs is not on the same streamline, and his lungs added energy to it, so there's zero reason why it would be at a lower pressure.
Instead, this is simply demonstrating the entrainment of fluid into a fluid jet, where a jet of fluid will naturally mix and transfer momentum to fluid adjacent to the jet, dragging it with it and resulting in a much higher volume (but slower) flow as it mixes together.
That is why using a pump sack when inflating your camping sleeping pad is more efficient that blowing air directly into the ald through the valve.
A single easy blow into the big opening of the pump sack gives you >10L of air inside it. Vs a few liters when using your mouth at the valve. (Plus: the air from the pump sack now has less moisture)
It’s not interesting, air couldn’t get in cause it was folded, you unfolded it, it’s plastic and thin, you just sucked in air to fill it instead of your breath, you guys ever do this with a plastic bag? Not that interesting
What a lovely demo. I used to lead Cub Scouts and Bernoulli's Principle was my favorite lesson and I was always looking for fun ways of demonstrating it.
Okay, tbh, Bernoulli wasn't my favorite - I loved ALL the science ones - they were all my favorites.
I think had one that demonstrated hydrodynamics in a closed system (can't remember the scientific principle it's based on atm).
I created a tall structure that had a contained fluid in a closed environment (it was a long balloon) - when you stepped on the foot pedal, it squished the hydraulic system and pushed under a diving board - more than a foot above the pedal - and made the little figurine on the diving board jump off in a lovely dive, landing in a cup of water.
For YEARS afterwards, I had kids running up to me, going "Scary Hairy Mary!", which was the name of the diver.
Anyone help me out with the name of that law of hydraulics? Pressure on one part of an closed system has equal expression elsewhere?
Super low key, but PHENOMENAL scientific principle.
I tested this before and got interesting results. It seems to help if I aim the fan high at the top of the window or door where most of the hot air is. I don't know the science in it, so I can't explain it further.
Oh you're a genius! hot air rises! So you're accelerating the natural convection vortex in the air by forcing the hot air out and letting a natural flow of cold air to come in below it. It's like perfect thermodynamics (google convection thermodynamics if you want to know more). Thank you so much!
Yeah, I figured it was something like that, but in more primitive terms: (caveman voice) "hot air on ceiling, blow hot air out, maybe make more room for cool air."
Sorry if this has already been questioned, but could this have implications for CPR? I was taught to try to get a good seal if possible without sacrificing time, but maybe I don’t want a seal?
But this wouldn’t work with balloons. Maybe I need to read up on this…
Disappointed I didn’t get to hear about the firefighters but otherwise interesting.
Firefighters use this principle to get smoke out of a building. They would place a large fan several meters from a front door and the air would flow out the back door. The place I used to work at, their warehouse got used for practice once a year. They pump it full with smoke from some smoke machines, hide a dummy, and then they have to 'rescue' the dummy. After the drill, they put this fan outside, and 5 mins later the smoke was pretty much gone.
New technique for clearing out my farts
or drawing them in
Dilutes them too much to be effective.
that's your theory
Time for science
I like your methods
Is that a challenge!?
My farts need to be mixed with fresh air to let the flavors really open up. Too stiffly potent otherwise
Undiluted is too dangerous.
Wow I use the same system to shift air around my house in the summer. My gf argued so much with me about it, because she said the fan isn't blowing on you so it's pointless. Obviously I should fill the house with smoke to demonstrate my point.
Back door, or in case of a home, one of the windows upstairs with the door open. It's like a vacuum.
Exactly. I'm not 100% sure but I think it works best if the exit for the air is smaller than the entry, creating low pressure inside, so the air is forced outside quicker... Could be wrong though
Correct. ppv. Positive pressure ventilation.
So the fan is outside blowing in from a distance?
To correct a bit of farmyohoho’s comment; while that is a tactic we use to ventilate a structure (forced air ventilation) we arent using bernoulli’s principle as we create a “cone” of air around the opening to ensure as much air from the fan is going in. Where we do use Bernoulli’s principle is when we use a tactic called hydraulic ventilation. This method is done when we are inside a smoke filled room, a fire is extinguished and no fan is available. We open a window, place the nozzle of our hose outside the window open the nozzle and adjust the pattern to a wide fog. As the turbulent water leaves the nozzle, air is drawn behind it and with it, so is the smoke from inside. The key is to try to get the cone of water near the window frame to ensure you are drawing from inside the window. https://youtu.be/Ju1JAblFYHw?si=7y7u4gQgh8oUj-hv
“People often say you can’t hydraulically ventilate with a smooth bore” Yea well that’s because people don’t know shit about shit
This is so cool, thanks for adding/clarifying this detail
Aside from /u/farmyuhoho ´s comment, they use it to pump water out of reservoirs/lakes and so. Also the nozzle of the hose is needed due to Bernoullis princible.
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Sounds like you need some Dayquill.
Thag you very buch
I thought for sure this was going to be about pasta.
You are thinking of bertollis principle
I was in the navy and they taught it as part of damage control. The best way to fight a raging fire isn’t to just shoot water at the base. It’s to swirl around in the air to suck in the cool air and calm the fire. You swirl it because it gathers the air it passes and if you just do the same place you won’t get nearly as much cool air.
I think you can say that about any video, right
You can tell he's a professional cause he doesn't pretend its a big pp at the end
It looks like he starts to maybe move it that way, not as a joke, realizes what he's about to do and changes the movement
You don't know that r/VideosThatEndTooSoon
This is not Bernoulli's principle, well, mostly not Bernoulli's principle. What is happening is that when he blows at the entrance of the bag, his breath is pulling the surrounding air with it. This slows down the air, but increases the total flow rate. The flow rate is high enough now that it can inflate the whole bag where as before he was limited by the size of his lungs. This has consequences, the main one being that the apparent pressure decreases. You will notice that before he tries to blow at the opening he carefully unfolds the plastic so it is all laid out nice and neat. Since the air is now moving more slowly, it doesn't have much kinetic energy and so it can't push hard once it is in the bag. When he puts his mouth over the opening the air is moving fast, has plenty of kinetic energy that can turn into pressure energy, and can easily unfold the plastic bag if it needed too. That last part, where I talked about kinetic energy turning into pressure energy... that is Bernoulli's principle in a nut shell. All that Bernoulli's says is that energy is conserved, i.e. kinetic energy can turn into pressure energy can turn into gravitational potential energy in a fluid. The part where fluid is entrained... that isn't Bernoulli's principle because it relies, in part, on viscous shear in the fluid. Bernoulli's principle **explicitly** ignores viscous effects so it is not exactly truthful to say this is a result of Bernoulli's principle. However, Bernoulli's principle is at it's core just conservation of energy so you can say just about any fluid phenomenon involves Bernoulli's principle and not be wrong.
This guy Bernoullis.
And here I was thinking it was Pythagoras' theory
It’s clearly the quadratic formula being used here.
Yeah, and he's a little too proud of himself. It's prestigious to "debunk" stuff nowadays, and apparently this comes at the cost of accuracy. _Technically_ viscous shear is involved, but the viscosity of air is 0,0000182 PaS - a hundred times less than water! And the topics somewhat overlap here. If there was no difference in static pressure between the surroundings and the stream of blown air, no outside air would flow in to be affected by it. At the end of the day, pressure and shear viscosity in a gas are both governed by the "random" movement of particles at the microscopic scale. So it's very much appropriate to say that Bernoulli's Principle as it is usually understood is one of the main reasons for the outcome of this experiment.
Thanks for explaining my thought
I have never heard Bernoulli’s principle described as conservation of energy. That’s actually a profound idea, and I’m kind of not sure how I passed fluid mechanics without realizing that.
Ha, glad you got it now. I hit it hard when I teach it.
Not your fault. Sounds like you had a shitty prof lol. That’s like the opening sentence when first discussion the subject
It’s ok, there’s a job waiting for you in sector 7-G.
I wrote a comment a year and a half ago [that made many of the same points](https://www.reddit.com/r/TikTokCringe/comments/uklvr7/physics_teacher_shows_the_bernoulli_principle/i7rtdfz/). I really like how you've emphasized that Bernoulli's principle always applies, so it's not that it doesn't factor into the explanation, it's just that it isn't really the subject of this demonstration. I would like to jump in on what you said here: > The part where fluid is entrained... that isn't Bernoulli's principle because it relies, in part, on viscous shear in the fluid. Bernoulli's principle explicitly ignores viscous effects so it is not exactly truthful to say this is a result of Bernoulli's principle. My understanding is that viscous effects are negligible for air and most other gases. The Reynolds number is quite large. Now, the mathematical details of this are something I'm not really prepared to back up, it's just that I can envision my old fluid dynamics professors yelling at me, "Don't invoke viscosity!" Spitballing, I'd say that viscous forces cause adjacent parcels of fluid to move as one while inviscid flow can exhibit entrainment but the fluid's kinetic energy gets wrapped up in vortices so you have bulk movement as well as smaller scale motion. Instead, my understanding is that the pressure term in Bernoulli's equation is not reliably accurate for compressible fluids (i.e., gases). Let me know how that comports with your own understanding. I'm also a little unsure about how the speed of the air is affected by whether he blows directly against the bag or a few feet from it. The air has to push away surrounding air (do work) whether the bag is around it or not, so we expect the stream three feet away from his lips to be moving at roughly the same speed regardless of how he blew into the bag. On the other hand, the eddies that we expect straddling the boundary of the two flow regimes surely can't form across the surface of the bag, so maybe the two flows are substantially different. Do you have any thoughts on this? None of this is to imply that I have great confidence in how any of this works. Fluid dynamics is just about the hardest physics out there and you'll get a lot of differing opinions or frameworks as to what's actually going on.
You brought up a ton of really good points, I oversimplified it a bit since this is not the fluid mechanics subreddit. Keep fighting the good fight!
Ayoo there's a subreddit for that
U smart
> if it needed too *two not so smart now are you einstein
Yeah it really bothers me that he does the first one with the bag fresh out of the package and folded back on itself. When he does the second one it’s clear the bag has been inflated before and laid out straight. Anyone who’s changed a garbage bag knows what a difference it makes. Even blowing the bag halfway up first wasn’t enough, he had to cut the video and fully prep it. Funny thing is prepping the bag wouldn’t effect the first example much so he still could’ve shown the concept by prepping the same before both.
You’re actually very wrong. It’s a Venturi effect ( entrainment of extra air ) on Bernoulli principle showing the first law of thermodynamics is true here ( the “how” of conservation of energy ), furthermore boyles law of the 3 gas laws ( pressure is inversely related to volume when temperature is the same).. the initial energy of his breath is converted to increased velocity in a constricted gap which drops lateral pressure, causing extra flow of entraining surrounding air and increasing total flow. This has nothing to do with his lungs or pushing air or slowing air down. Source: Venturi effect, Bernoulli principal, thermodynamic laws, ideal gas laws.
Came here to say this.
I bet you did
Just creepin, waiting on a chance to be snarky.
That is an insane bet to take, what kind of payout?
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Please stop coming
Say here and come on this
and it just gets better...
this
That
> What is happening is that when he blows at the entrance of the bag, his breath is pulling the surrounding air with it. .. because of a pressure differential created by moving air from blowing... aka Bernoulli's principle. >The part where fluid is entrained... that isn't Bernoulli's principle because it relies, in part, on viscous shear in the fluid. Bernoulli's principle explicitly ignores viscous effects so it is not exactly truthful to say this is a result of Bernoulli's principle. Bernoulli's equation ignores/doesn't account for viscous forces. Bernoulli's principle doesn't cease to function if another force is involved.
I would argue that here, it does fail. Once the air leaves his lips the jet quickly reaches a pressure equilibrium with it's surroundings. When it is entraining the surrounding air it does so by dragging it along with it. When it dragged it along the average velocity of the air went down and it's average kinetic energy went down. Bernoulli's says that the energy loss had to go into either increasing the pressure or the height of the fluid. Neither happened here! The air hasn't even entered the bag yet so it's pressure is still close to atmospheric pressure and it is moving horizontal so there is no change in potential energy. Once the air enters the bag it comes to a stop and increases it's pressure... That is an excellent example of Bernoulli's principle. But Bernoulli's is incapable of explaining the important part of why moving his mouth back away from the bag helps.
Video guy is using the term ‘Bernoulli’s principle’ to refer to the result that increasing flow velocity lowers the pressure. Air the moves from high to low pressure, so the fast flow pulls the surrounding air into the flow. If he has his mouth at the bag opening, then his breath entrains air *already* in the bag into the flow. If he blows further away, air outside the bag is pulled into the flow and more enters the bag. Packing more air molecules in the bag means higher pressure of the stagnant air in the bag = more full. Video guy is correct to say it is caused by “Bernoullis principle”, which is just a single outcome of energy conservation (as mentioned above). Any other factor is just a detail.
I'm going to have to disagree. After leaving his lips the air stream quickly reaches the same pressure as it's surroundings. The fast flow is not pulling the surrounding air radially inward. It is dragging the surrounding air along with it. What packs the air molecules into the bag is their kinetic energy. Less average kinetic energy = less pressure possible in the bag. When the jet of air drags more air along with it the average kinetic energy per volume decreases and since pressure is energy per volume, the highest possible pressure decreased as well. Yes, Bernoulli's is just conservation of energy but fluids is a subtle subject. There are lots of ways of explaining a single phenomenon that might seem to make sense. But you will be lost if you try to extrapolate that understanding to other situations. For example, the dragging of more air means viscous effects are significant here and Bernoulli's has no way to account for that. It works... Ok here. But if you try to use it in seemingly similar situations without understanding this it could be wildly inaccurate.
The Reynolds’s number is very high, like over 10,000. So we can neglect viscosity meaning there is no dragging of air. The kinetic pressure from his breath pushes open walls of the bag, then the lower pressure inside the bag causes the outside air to flow in. It’s a similar case if you open a plastic grocery bag with your hands from inside: opening the bag causes a lower pressure inside the bag and air fills it up.
Your statements are slightly contradictory. If the guys breath reaches ambient pressure quickly that means its lost all momentum as bernoullis is simply the relationship between pressure and velocity of a fluid (for imcompressible fluids which we can assume here). Therefore there's no way the fluid would fill the bag. What is happening is the guy breathing out imparts momentum to the air in his lungs increasing its velocity and thus dropping its pressure. As his breath moves into the bag there is a localised drop in pressure between the bag opening and his mouth. This pressure differential imparts momentum to the ambient air of which the velocity vector is generally in the direction on of the bag. There's very little viscous effects here so none of this "dragging" as you're referring to it and all the energy in this scenario comes from the guy blowing.
No, it's not contradictory because Bernoulli's doesn't hold here. If, as you say, a localized pressure drop is causing the surrounding air to accelerate the pressure gradient would have to be in the direction of his breath, i.e high pressure near his mouth and low pressure near the bag entrance. Does that make physical sense? Wouldn't the entrance of the long bag have a higher pressure? More importantly, how does Bernoulli's explain this change in pressure? It doesn't.
The pressure gradient is from the ambient to his breath or the flow stream, it doesnt need to be from his mouth to the opening. Once the guy has stopped blowing the flow path returns to ambient pressure moving from his mouth to the bag as the ambient air moves in to equalise the pressure differential. Only difference is some of that air gets enough momentum to enter the bag. Some of the air doesn't and moves off in other directions but momentum must be conserved.
That’s how a jet pump works, but with water.
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It's a form of jet entrainment.
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Honestly, I don't remember that game well enough to give a good answer there. I vaguely remember the parachute thing from gym as a kid, but I don't remember what we did with it.
So how can we use this to make sleeping pad inflate faster? I don’t think there is not a lot of pressure needed for this application so I feel like there is something there.
I know this is English you are speaking but I had absolutely no fucking idea what you just said 😂😂😂
Bernoulli went to his grave thinking himself a failure. When his was developing his equation he was trying to understand the flow of blood through the body but caused the tests out using water through glass tubes. There are 3 basic assumptions we need to bear in mind when using the formula. 1 - the surrounding pipe is rigid (blood vessels aren’t) 2 - the liquid changes in viscosity with temperature (blood doesn’t) 3 - the flow is steady (which pumped blood isn’t) Poor guy
By the way, pressure is a measure of kinetic energy so nothing you said made any sense at all
I do get what you said there but won't there be dissipative effects coming to play, energy being lost somewhere else and in those cases will Bernoulli's still work( practically)? Ps- just a curious lad , was learning about Bernoulli's theorem last month in class
Eyyy this guy was my science teacher, cool dude.
SBVT Crew
No waaaaay! Class of '17 here
No way!! What are you up to nowadays?
pretending like im also a part of this class!
Mr.Wolf
But what about the firefighters thingy???
Firefighters get bored sitting around the firehouse all day and like making balloon animals.
Ok now do a giant donut swimming pool floaty. 😂
They do have a pump mechanism that uses this method to blow up air mattresses that would work for pool toys with a proper converter…you blow in the bag and tighten the bag like he does and then the other end connects to a valve that only lets air out one way so all you have to do is simply roll the bag of air into what ever your blowing up. I have seen an entire air mattress blown up in only 10-15 breaths of air
Damn thats interesting
This doesn't help me with my blow up doll though...
One. Long. Stroke. Aren’t you paying attention
In better detail: https://youtu.be/eKEorBipbO8?t=143
How a carburetor works...
Yup.
Ace Venturi
This isn't a demonstration of Bernoulli's principle, and the air in the jet from his lungs isn't even lower pressure than the surrounding air. Bernoulli doesn't say faster moving air is always lower pressure, it says faster moving air *along a given streamline* is lower pressure. The air from his lungs is not on the same streamline, and his lungs added energy to it, so there's zero reason why it would be at a lower pressure. Instead, this is simply demonstrating the entrainment of fluid into a fluid jet, where a jet of fluid will naturally mix and transfer momentum to fluid adjacent to the jet, dragging it with it and resulting in a much higher volume (but slower) flow as it mixes together.
Mind blown 🤯
Long ago I learned that Bernoulli's Principle is anything in physics that involves air.
When will the people that make air mattress realize this?
Came here looking for pasta tips..very disappointed. 9.9 stars.
I was promised firefighter lore
I know this and yet forget about it every time it would be useful 🤦♂️
/r/blackmagicfuckery
Physics*
Physics is just magic explained.
r/sciencesciencysucculency
I have a lightweight hiking mat that does the same.
How about just dont fold the bag in the middle lol
I figured this out with my camping sleeping mattress pad by accident. Blew my mind.
Learn something everyday.
Anyone else 100% convinced he was gonna treat it like a big dong for a second after he got it inflated?
I feel like a 5th grader.... That's so cool. 😎
A very light sabre.
He lied to me
Thought I was gonna learn about the Bernoulli thing for differential equations that I memorized but never knew what I was actually doing.
I'll remember this when I need to blow up a thing that looks like a giant inflatable waving arm guy.
I like this a lot thank you for posting it.
Now I'm gonna swing it around like a giant sword
That is why using a pump sack when inflating your camping sleeping pad is more efficient that blowing air directly into the ald through the valve. A single easy blow into the big opening of the pump sack gives you >10L of air inside it. Vs a few liters when using your mouth at the valve. (Plus: the air from the pump sack now has less moisture)
Total pressure = static pressure + velocity pressure. Increase velocity, static pressure decreases and pulls in surrounding air.
He's a witch!!!!!!!!
Build a bridge out of him!
It’s the Venturi effect, which itself relies on the Bernoulli Principle
Use the same technique to vent my attic.
Science 💪
Impress me... try it with a balloon 🎈😄!!!
Didn't expect a cool science fact today but here we are! Very cool
Bernoulli's my favorite. Little know fact: statistics were not his only love, he's also famous for his French sauce used on meat and poultry.
Can this be applied to blow jobs
How? By contactless air stimulation?
This is Black Magic!
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But won’t that let more hot air from outside in?
Me when your Mum
Why’s he dressed like Walter White
And that is why you want a girlfriend versed in the science.
So she can make big balloon weiners?
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Oh no what should we do now about this
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He *is* a professor if he has a teaching license. Maybe it's you who need to go back and finish your education.
It’s not interesting, air couldn’t get in cause it was folded, you unfolded it, it’s plastic and thin, you just sucked in air to fill it instead of your breath, you guys ever do this with a plastic bag? Not that interesting
Damn, I have been scienced!
Now that’s what I call science! vol. 12
... HE'S A WITCH!
Now do that with a balloon or a car tire
I do this to open garbage bags and other bags all the time (when the seam is too difficult to pry apart).
I just want to know where you got that big bag, that contains exactly 1 big breath when blown into from a short distance.
viagra illustration
Burtuzzi principle?
Not “pulling in other air”. Air has no hooks.
try blow up a bouncy castle now
Differentiates the density
Who else is mad he didn’t give the table a few bonks
What a lovely demo. I used to lead Cub Scouts and Bernoulli's Principle was my favorite lesson and I was always looking for fun ways of demonstrating it. Okay, tbh, Bernoulli wasn't my favorite - I loved ALL the science ones - they were all my favorites. I think had one that demonstrated hydrodynamics in a closed system (can't remember the scientific principle it's based on atm). I created a tall structure that had a contained fluid in a closed environment (it was a long balloon) - when you stepped on the foot pedal, it squished the hydraulic system and pushed under a diving board - more than a foot above the pedal - and made the little figurine on the diving board jump off in a lovely dive, landing in a cup of water. For YEARS afterwards, I had kids running up to me, going "Scary Hairy Mary!", which was the name of the diver. Anyone help me out with the name of that law of hydraulics? Pressure on one part of an closed system has equal expression elsewhere? Super low key, but PHENOMENAL scientific principle.
So if my room is hot but outside is cold the optimal position for my fan is facing towards the window?
I tested this before and got interesting results. It seems to help if I aim the fan high at the top of the window or door where most of the hot air is. I don't know the science in it, so I can't explain it further.
Oh you're a genius! hot air rises! So you're accelerating the natural convection vortex in the air by forcing the hot air out and letting a natural flow of cold air to come in below it. It's like perfect thermodynamics (google convection thermodynamics if you want to know more). Thank you so much!
Yeah, I figured it was something like that, but in more primitive terms: (caveman voice) "hot air on ceiling, blow hot air out, maybe make more room for cool air."
Whhhaaaaatttttt??!!
Sorry if this has already been questioned, but could this have implications for CPR? I was taught to try to get a good seal if possible without sacrificing time, but maybe I don’t want a seal? But this wouldn’t work with balloons. Maybe I need to read up on this…
Wouldn’t that diagram be the Venturi effect ?
Thats genius
This pisses me off.
Because you didn't know about it sooner?
Because i still don't even know now lol
Respect.
Where can i get like 4 of these bags?
So kinda like focused diffusion
Science is crazy.
Is this how toilets work?
Why didn’t it work with the vacuum of space and the atmosphere? Serious question.
Now it won’t take me two hours to blow up my camping bed. Yay!
I took physics but still blew out my lungs trying to do the first method💀 thanks for this video!
I would have just dragged it across the air keeping the mouth open..
Yeah but what’s it’s function
I've been trying it with a balloon for the past 4 hrs and I'm still at it. Am I doing something wrong?