okay everybody today we're going to be seeing if things sink or float when they're in a vortex and a vacuum chamber now this is a really interesting question let me explain what I mean so I have here a ping-pong ball and you see that it floats in water pretty easily but now watch what happens when I turn this stirrer on and start stirring the water oh there it goes it's getting sucked down to the bottom of the water so for some reason when I start stirring the water the ball gets sucked down it
stays there it's sucked to the bottom of the container so why is this happening why is it that the ball gets sucked down to the bottom when the water starts moving and then you can see when I turn off the spinner it pops back up so as soon as I stop the water spinning very fast the ball floats back up so this is actually really interesting and the reason it's happening is because whenever a fluid moves fast the pressure automatically lowers so let me show you what I mean so say I want to suck so
me water up from this straw but I don't want to touch the straw I can still suck water up by just blowing air over the top of it so I've taped my straw on the end here and now I'm just gonna blow over it so you can see it just spraying water out of the top and that's happening just because I'm blowing air over the top of it and the pressure is lower so it's essentially getting sucked up the straw without even touching the straw you can see a little bit clearer when I use a clear straw so you can
see the water be drawn up it so you can see when I blow how the water rises up so now that we understand that moving fluids cause lower pressure now we can start to understand why this ball would sink so as the spinner starts to spin it drags water around with it and since that water is moving fast it now has lower pressure and the water at the center is moving faster than the water on the edges and so that means the water at the center has lower pressure and so that means that it has lower pre
ssure than even the atmosphere above it and so the atmosphere starts to push down into it you can see the atmosphere started to push the air down until it hits the bottom and so that push of air down is happening because the water actually has lower pressure than the air above it and so when you stick a ball on it there's lower pressure in the center of the vortex and so the ball now gets sucked down but here's the interesting part I told you that the reason the ball is getting sucked down is be
cause the water is moving and so it has lower pressure and the only reason it causes the ball to go downwards because the atmosphere above it has higher pressure than the water now so that got me thinking is it really the atmosphere that's pushing the ball down or is just the movement of the water dragging it down well if I understand the sucking motion of vortices then to me it just means that the reason that they suck things in is because the water is moving faster and so they have a lower pre
ssure than the atmosphere so if we took away the atmosphere that would mean there's no sucking motion so today I'm going to stick this in the vacuum chamber and see if when we create a vortex that the ball stops getting sucked down because there's no atmosphere to push it down so let's see if that happens in the vacuum chamber well the ball sink our float in a vortex in the vacuum chamber okay let's put our ping pong ball on start the vortex you can see it starts to sink now now let's create a v
acuum in there and see what happens okay three two one okay we're at 0.7 atmospheres point six out miss fears okay we're at point three atmospheres now I don't know it's still sunken down there Oh point two atmospheres we're getting a lot of dissolved bubbles coming out of there now a lot of the dissolved air is coming out of the water Oh interesting is starting to come up no way we're at point one atmospheres and it's not sinking anymore I'm starting to flow up so you can see this air pocket be
low it's starting to kind of push it up no way so I only guess this would happen I had no idea if it would really work but it looks like it really worked it's not sinking in a vacuum that's so weird so basically it's not sinking down because even though the water is moving really fast there's barely any atmosphere there to push the ball down okay now I'm gonna lift the air back in and see if it sinks back down three two one [Music] so as soon as I let the air back in it starts to push the ball b
ack down that's so cool now at full pressure again it's completely submerged okay so this is a really cool effect basically even though you have really fast-moving water in the center of the vortex and that fast-moving water is creating low pressure it doesn't really matter because the atmosphere around it in the vacuum is also low-pressure and so there's not this force pushing it down like there is an atmosphere so another cool test would be does that mean that in a high-pressure chamber a vort
ex has even more sucking motion I don't have a way to set that up right now but that would be a cool experiment to try and also I'd like to think brilliant for sponsoring this video so people often ask me how they can learn more about the concepts that I teach in my video and brilliant is an awesome resource for that so brilliant is a really cool website and also it's an app which helps you learn by getting used to solving interesting problems and science mathematics and computer science and eac
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Comments
As some have pointed out there is definitely more going on here than just air pressure. In fact you cannot talk about any fluid flow with only talking about pressure. You have to always talk about fluid velocity and pressure together. We do know there is the centrifugal effect of water being thrown out the sides and also down the middle. But the reason there is ever any flow at all is due to pressure differences. The ball is being dragged down by the water but it is also moving fast and so the atmosphere pushes it down as well. There is also rarified air and eater vapor that forms under the ball pushing it up (maybe). This is definitely a phenomenon that I have never seen before in any literature so if anyone has any resources are open to hear more about this.
The type of 'spinner' you used has a serious effect on this experiment. The agitator at the bottom, is in effect, a sort of centrifugal pump. Water is constantly being flung outward at the bottom, then forced up the walls of the container and flowing back in toward the center (all with considerable tangential flow as well). (this is why this type of 'mixer' is so often used, it circulates the fluid both tangentially around the container, but also radially outward, upward, and back down in the center) This downflow in the exact center, IMHO, is what drags the ball below the surface. After all, when the ball is completely submerged, the air isn't acting on the ball at all. As others have pointed out, as the water spins around it also has centrifugal forces acting on it, so the surface of the water is always perpendicular to the combined centrifugal/ gravitational forces acting on it. It would be very enlightening to use a different mechanism to 'spin' the water. For example, remove the agitator and spin the entire beaker. With all the water spinning at the same RPM, you would not set up the same internal flow pattern. The water at the bottom would not be 'pushed' outward to the walls of the beaker any more than any other water, so there should not be any 'vertical' circulation. Edit: Without this, I predict the water will form a parabola, but the ball will not be 'sucked/pushed' under the surface (much like you saw it under the high vacuum condition).
Alternative explanation: the "air pocket" at bottom (under vac) is actually boiling water.
You would need to also do the test with starting the whirlpool after the vacuum reaches least pressure for this to cover all the bases.
Waauw Action Lab. You invented a simpel physics-setup that causes discussion among physicists! I envy you! I have my doubts about your explanation, but I cannot come up with a better one (yet).
Atmospheric pressure, Vortex, Effect of air movement all covered in just 1 short video... Awesome!
I swear one of those droplets of water hit my face when he was blowing the straw, so weird...
Each of these videos is worthy of a 10th grade science assignment. I sourced and got inspiration for one of my assignments in the action lab video about heating up water by blending/stirring it. I conducted my own experiments and ended up getting full marks. Thanks for the effort and information put into these videos.
Man you constantly come up with original and interesting experiments. Happy to say this is not some pop science channel. Your really teaching lots of people obscure and interesting science.
As has already been pointed out - Water boils under vacuum. The cooler the water is, the lower the atmospheric pressure needs to be to reach the boiling point. With a low enough pressure, tap water will boil at room temperature. Yes, that's a Fact!. If you place the ball on still water and then pull a vacuum, the water will boil all around the ball like a pan of water on the stove, only the water will NOT be hot to the touch. As the air is evacuated from the chamber water will reach a point at which it boils. Right after this, the vacuum gauge will stabilize and stop dropping until all the water is gone, then it will drop to whatever level your pump is capable of pulling on your vacuum chamber. In your experiment, the "air pocket" that formed under the ball while rotating the water is the water's gaseous state trying to reach the surface. This action creates a lifting force. The bubble formes in the middle of the vortex since this is the water's lowest pressure point. Going a little off subject. Something else interesting about water is it has a "triple point". That is the temperature and pressure at which the three phases (gas, liquid, and solid) can coexist in thermodynamic equilibrium. Under the correct circumstances, water can turn directly from ice (a solid) to gas without first becoming a liquid.
Got my subscription box yesterday !! Bit late but hey, I am sure there were good reasons. It had more than I thought it would. Quality hoses, brass fittings, thread tape for fittings, 2 wrenches, a vac gauge, patch,sticker, pin, instruction book and experiment book ,box with marshmallows -balloons - shaving cream. I like it all. Hope the next one is a bit more timely but I am sure you all were making a great effort. Maybe you got more orders than expected or ?? Thanks..
As a college graduate in physics from 101-499, I didn't even expect this... I anticipated that no matter how low you drop the atmospheric pressure outside, the pressure will always be lower once the water starts spinning, there for keeping the ball at the bottom... Where did my calculations go wrong? I'm confused... Lol But anyways, no matter what I have learned in my lifetime, I always seem to learn something new on this channel! Keep up the good work!
ACTION LAB!! ACTION LAB!! ACTION LAB!! Let the legend continue
Great experiment! Overall air pressure has no direct effect on the ball - it pushes it down (via water) as much as it pushes it up. But the lower pressure allows building of steam- bubbles. They gather in the middle where the pressure is low and they build eventually a vapor column that wants to go up and pushes up the ball. It would be interesting to see the experiment with slightly warmer or colder water...
It would be so much fun to have this kind of dad. Never gets boring
Stupendous visual at low pressures! Did you see that? the level of control of the ball height with pressure? Amazing
There's a reason I love this channel. It teaches things books doesn't
That little experiment that you did with the straws also illustrates how carburetors work. As intake air flows at extremely high velocities into the barrel and through the venturi, it has extremely low pressure that sucks fuel out of the float bowl and into the intake to join the air rushing into the engine. Carburetors aren't used on cars anymore; they're exclusively fuel-injected now. But carburetors are still extremely common on GA aircraft, particularly those powered by Continental or Lycoming motors.
You're always able to explain what you're doing really easily and the subjects are fascinating. Thanks
Hey I have to commend you on your awesome videos, I've learned a lot! One thing I must offer up in this one is, in the first case, it actually sinks for two reasons. First, centrifugal force and buoyancy act outward instead of downward as with gravity only. Second, the mixer is a turbine. It's pumping, sucking the water down from the centre (where the ping-pong ball is) and throwing it outward and up the beaker walls. A common statement of Bernoulli's principle, the well established concept that a fast moving fluid is simply at lower pressure than anywhere downstream, is false. The common diagram of two large pipes connected by a smaller straight section of pipe, with a manometer connected midway in each section, showing reduced pressure at different points, may indeed work as depicted, but it is an incorrect way to measure pressure in a moving stream. The reason for the above is because of the effect of the boundary created by the measuring tube. The same effect is created by the trailing edge of a venturi, tending toward the suction which causes gas or droplet entrainment. The correct way to measure pressure would be to have a pressure transducer surface flush and nearly indistinguishable from the interior surface of the passage it is measuring. This way there is no disturbance to the flow, and so the pressure measurement would prove independent of flow. The diagram depicted above, applied to a venturi, with or without the correction last stated, would work as depicted because the measuring location is at a change of flow shape/velocity.