Duration 10:44
Levitating objects in a stream of air.. Coanda effect // Homemade Science with Bruce Yeany
Published 4 Apr 2021
Tired of seeing the ping pong balls, beach balls, golf balls or a screwdriver float in a stream of air? I was, so I looked around andfound some other objects that demonstrated the same principles. In my investigations I found that the objects were supported by two different means. Some objects were supported from below directly by the air air stream itself. Other objects used the Coanda effect to decrease the air pressure above the ball allowing the atmospheric pressure to support the object, in some cases it is probably a combination of both methods. This has been a fun and interesting investigation and I was able to find enough objects that they will be shown in at least two parts. Enjoy the video and if you have any suggestions, add them to the comments, I do read them. My compressor: I had a few people ask about it it's old and loud, so I ran it outdoors away from the house and ran 100 feet of air line portable 8 gallon, 2 horsepower, rated for 125 PSI. with 6.3 cubic feet per minute recovery. It was more than enough for these demonstrations
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As a fellow science educator, it's difficult to state how valuable your channel is.
Thank you sincerely! 5
The world seems to be getting digitized too much so people started to forget how cool the practical science is.
Thanks Bruce
Good reactions catching every object that went crazy there too!
I really enjoy your experiments. Thank you for sharing. ...
I was really amazed by the baseball bat until I figured it to be one of those hollow plastic ones. 😊 ...
You are the best Bruce!!!
, but bats and other objects that you tried simply blowed my mind! Looking forward trying this by myself. Thank you!
The idea would be to see if it would make the object rise higher.
Congratulations for this experience Bruce!!!
I hadn't seen your videos in a while and stumbled across this. You really took a deeper look on this one and that is very good. I like the way you must look deeper into things and I encourage this. I'd love to chat with you some time. You mention a follow-up video, but I don't see a link..?..
I wonder if the science you 'get to' there is some of the following.
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I'm glad you're recognizing the Coanda Effect. Coanda himself recognized the lowered pressure because of the curved flow. <-- NOTE : it is the curved flow that is the cause.
Do you talk about some of the following.
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It is the inertia of the air as it curves that tries to go straight, thus reducing the pressure. It is why you swing outward on the playground merry-go-round, or why you feel lighter at the top of a roller coaster hill. Your inertia is trying to carry you straight. This is described in Newton's First Law.
With air, the atmospheric pressure holds it against the curve, but the tendency to go straight works against atmospheric pressure, thus reducing the pressure near the surface.
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With the sharp edge, air's inertia is enough to take over; atmospheric pressure is not enough to make the air turn so sharply at the edge. So, the flow does continue straight and atmospheric pressure pushes air in behind the edge and we have considerable turbulence as the flow mixes with the stationary air past the edge.
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However, at and again at , you seem to be implying that the stream of air is at a pressure lower than atmospheric pressure. This is a very strong, old myth and simply isn't true. It can be easily measured as is done when studying it in aerodynamics with a static pressure probe.
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With the paper, it starts as Coanda, but as the paper straightens, the air is pulling the paper straight due to the air slightly sticking to the paper with viscosity and is trying to drag the paper along with the fast air. If you measure tension on the paper, you will see that it increases as the paper straightens. That tension is enough to lift the paper - just as if you only pulled on the far end.
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With the inverted bat, you again imply the stream pressure is lower on that side. However, it isn't and you seem to ignore Coanda still occurring at the (now) bottom. If you look more carefully at the angles you will see that the Coanda at the bottom is working sideways and down - as air follows the curve part way. The tension on the string will increase due to the net downward force as Coanda reduces the pressure under the bat and the atmospheric pressure on top is still pushing normally. The sideways component of the Coanda lowered pressure is what allows atmospheric pressure push the bat into the curved flow. Coanda only occurs about half way around the end, so there is a sideways component.
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At you correctly recognize the upward component from Coanda - that is still happening on the inverted bat. Do you see that?
Also, there is also some drag from the moving air along the side of the bat, but not a lower pressure.
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If so, I'm sorry to hear that you are still in the camp that says "fast moving air has (or causes) a lower pressure".
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Best regards and best wishes for a good new year.
Science Vigilante, Steve. ...
Is there a theoretical limit?
But I got puzzled by the Coanda explanation of lift...
I thought the deflected stream of the Coanda effect was also producing lift. Not only the partial vacuum and the atmospheric pressure, but also this downward stream of air, due to Newton's law. I can't find anything conclusive, but maybe trying a bat with a bell shaped tip.
I mean: the bat has a semispherical end that deflects the stream downwards due to Coanda effect which causes a partial vacuum but also a flow of air downwards.
If somehow the downward stream were annulated... I'm thinking of a bell because the top would still be semispherical, but the "skirt" or rim of the bell, would redirect the downward stream of air, to the sides, thus rendering any downward flow of air to zero, and isolating the atmospheric pressure related lift, to my hipotetical "2nd law of Newton lift"
All of this comes from somewhere I read about a Coanda airplane, plus the famous 60's experiments with flying saucer prototypes...
(I have no air compressor to test myself...so I ask for some help)
Thanks!! ... 1
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