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Balloon in a bag - measuring pressure
#1
Happy holidays!

Here is hopefully a contribution to pV=nRT experiments with phyphox.

Put a balloon in a bag together with a phone and pop the balloon with a needle.

Please find my first try attached.

I cannot explain why there are two pressure peeks?

There's 0.04 seconds between each measurement and 0.28 seconds between the peeks (1015.4 and 1015.5 hPa). Pressure in the room is something like 1013.7 hPa.

Best regards.

//Erik


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#2
An experiment with better control:
https://phyphox.org/forums/showthread.php?tid=1333

I tried experiment of Eric and I got 2 peaks and then more...

   

Put a smartphone inside a balloon, blow up it and pop with a needle.. Pressure just dropped to the initial value.. As expected.

   
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#3
(12-25-2021, 06:49 PM)solid Wrote: An experiment with better control:
https://phyphox.org/forums/showthread.php?tid=1333

I tried experiment of Eric and I got 2 peaks and then more...



Put a smartphone inside a balloon, blow up it and pop with a needle.. Pressure just dropped to the initial value.. As expected.

Hmm... my phone is too big. But I guess you used the same equipment as in the CpCv-article? (jar and bottle connected)

If you did, may I ask if you used a standard off the shelf supermarket balloon (see attachment)? I mean, my peak is just ~2 hPa higher than the room pressure, but your balloon seems to hold a pressure 7.5 hPa higher than the pressure in the room?

The second peak is probably me holding the bag in a tight grip. I can easily get 20 hPa peaks just from squeezing an empty bag with a phone inside (see attachment), so the second "pop peak" is probably me reacting to the "pop".

I will try again with less excess air in the bag, maybe I'll then get closer to the true value of the pressure inside the balloon when I pop it (which is 7.5 hPa?).

Best regards.

//Erik


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#4
Eric,

I have not used my SensorTag for this experiment, I used my phone 7x13.5 cm.
I used a standard balloon but from another supermarket shelf...

I think the additional peaks are due to jumping of the phone inside the bag. What I expect and do not see it is a pressure razing inside the bag. I will repeat your experiment if I will find a sufficiently hermetic bag ...

Nice vacations
Mikhail
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#5
(12-26-2021, 02:58 PM)solid Wrote: Eric,

I have not used my SensorTag for this experiment, I used my phone 7x13.5 cm.
I used a standard balloon but from another supermarket shelf...

I think the additional peaks are due to jumping of the phone inside the bag. What I expect and do not see it is a pressure razing inside the bag. I will repeat your experiment if I will find a sufficiently hermetic bag ...

Nice vacations
Mikhail

Thank you Mikhail! I would never have tried to put the phone inside the balloon if you had not done it.

The whole purpose of the putting the balloon inside the bag was to figure out a way to measure the pressure inside the balloon without having to put the phone inside the balloon. I just though, without trying, that was not possible!

Turns out it was possible, and my phone says the pressure was 1049.27 hPa at 47.21 seconds and 1012.76 hPa at 47.25 seconds. Average pressure in the room during 9.2 seconds after the pop was 1012.68. It took about one minute from start to stop.

I found a student paper on balloon pressure measurements which shows a similar result. Their balloon pops at around 30 hPa above room pressure (see figure 4 page 6).

Remains to explain why I only got a 2 hPa peak out of a 35 hPa balloon...

Best regards.

//Erik


Attached Files Thumbnail(s)
   

.pdf   Lufttryck i ballong laboration Mätteknik.pdf (Size: 795.54 KB / Downloads: 212)
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#6
Smile Wink Wink Wink Wink
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#7
To explain why only a 2 hPa peak (or peaks) are obtained out of about 35 hPa pressure in the balloon is really a question.

First of all I have verified pressure in the balloon blowing up.  The technique using the SensorTag and a small jar which is cited above was applied. It gave also the maximum pressure of about 50 hPa (the pressure were reducing with the balloon growing, see figure).

   

Then the experiment of Eric was repeated with the black balloon. The material used is on the photo below. The needle was initially inserted in the wine bottle cork to pop the balloon inside the bag (and not trough it in order to preserve its hermeticity ).

   

The pop sound is so strong that the measurements by the SensorTag were stopped. The phone measured some peaks of about 2 hPa as is presented by Eric.

   
No explanation for the moment...
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#8
(12-27-2021, 12:13 PM)solid Wrote: To explain why only a 2 hPa peak (or peaks) are obtained out of about 35 hPa pressure in the balloon is really a question.

First of all I have verified pressure in the balloon blowing up.  The technique using the SensorTag and a small jar which is cited above was applied. It gave also the maximum pressure of about 50 hPa (the pressure were reducing with the balloon growing, see figure).


Then the experiment of Eric was repeated with the black balloon. The material used is on the photo below. The needle was initially inserted in the wine bottle cork to pop the balloon inside the bag (and not trough it in order to preserve its hermeticity ).


The pop sound is so strong that the measurements by the SensorTag were stopped. The phone measured some peaks of about 2 hPa as is presented by Eric.

No explanation for the moment...


I popped 4 balloons with about 2 seconds interval but without any bag to see if I could get a pressure peak at all "out of thin air". I got two minor minima (not peaks!) that is probably from the last two balloons popping: 1007.53 and 1007.51 when average pressure was 1007.70 hPa (I should have measured when the pops happened with the Acoustic Stopwatch but I haven't mastered programming phyphox experiments yet).

So the immediate release of about 4.5 liters of 35 hPa air (without anything but air containing the release) somehow registers a decrease in air pressure.

Apparently, after an explosion, you can have a "negative pressure zone" and a "subsequent oscillation zone":

https://doi.org/10.1016/j.dt.2019.04.014

Not sure we're measuring any of that stuff, but in theory we might be doing exactly that!

Best regards.

//Erik
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#9
Our bag is not blown up and a very small increase of the air volume inside it ΔV (Δp/p)V = 0.03 V  does not increase the pressure inside (Δp=30hPa, p=1000Pa). Only a small peak when the bag adopts the new volume (its mass is not zero!) will appear. When I hit the bag with some air inside I observe a single sharp peak of about 1hPa (see the figure).

   

The origin of multiple peaks is still unclear.
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#10
(12-28-2021, 02:52 PM)solid Wrote: Our bag is not blown up and a very small increase of the air volume inside it ΔV (Δp/p)V = 0.03 V  does not increase the pressure inside (Δp=30hPa, p=1000Pa). Only a small peak when the bag adopts the new volume (its mass is not zero!) will appear. When I hit the bag with some air inside I observe a single sharp peak of about 1hPa (see the figure).


The origin of multiple peaks is still unclear.

So the first peak could maybe be interpreted as if the bag has been hit on the inside? Or even that we are actually seeing the sound of the pop hitting the phone's sensor rather than hitting the bag? Or both?

"What Does Sound Look Like?"
https://www.youtube.com/watch?v=px3oVGXr4mo

And look here! https://en.wikipedia.org/wiki/Sound_pres...d_pressure
9-inch (23 cm) diameter balloon popped with a pin[18] 0 m 1.13 kPa
9-inch (23 cm) diameter balloon popped with a pin[18] 1 m 282.5 Pa

What is that pressure sensor made of anyway? How does it work?

Best regards.

//Erik
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