Liquid soap pulsing as it's drawn into a syringe

  • Context: Undergrad 
  • Thread starter Thread starter puc
  • Start date Start date
  • Tags Tags
    Liquid Soap Syringe
Click For Summary

Discussion Overview

The discussion revolves around the phenomenon of liquid soap pulsating as it is drawn into a syringe, as observed in a slow-motion video. Participants explore the underlying physics, including the effects of resistance, elasticity, and potential vortex formation, while considering various factors that may influence the behavior of the liquid soap in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants suggest that the pulsations may result from a combination of resistance and elasticity in the soap, which has long molecules that can build tension.
  • Others propose that a vortex forms just behind the syringe opening, causing the soap to be pulled forward as it is drawn in.
  • One participant notes that the presence of bubbles in the soap may lower its modulus compared to a bubble-free solution, drawing a parallel to vibrations in wind instruments.
  • There are suggestions that the driving mechanism for the syringe may not be properly decoupled, or that the tube itself may be springy, contributing to the observed behavior.
  • Some participants speculate that the oscillations could involve the mass of the syringe and the modulus of the liquid, or the behavior of a compressible viscous liquid.
  • A participant mentions the possibility of using a more rigid syringe or different driving methods to investigate the oscillations further.
  • Another participant highlights the importance of a stable mechanical setup to ensure consistent force on the piston, as the current setup appears to be unstable.
  • Responses from the original video poster indicate that they have observed similar effects with clear soap and are considering further experiments with different materials.

Areas of Agreement / Disagreement

Participants express a range of hypotheses and observations, but there is no consensus on the exact cause of the pulsations. Multiple competing views remain regarding the mechanisms at play and the influence of various factors.

Contextual Notes

There are limitations in the discussion, including missing details about the mechanical setup driving the piston and holding the syringe, which may affect the interpretation of the oscillations. The role of bubbles and the specific properties of the soap used are also not fully resolved.

Who May Find This Useful

This discussion may be of interest to those studying fluid dynamics, material properties, or experimental physics, particularly in the context of non-Newtonian fluids and their behavior in confined spaces.

puc
Messages
9
Reaction score
1
TL;DR
I asked NIK282K who watermarked the following one minute video if I could post it here to see if anyone might be able to say exactly what is happening and explain it. Yes was his answer.
  • Like
Likes   Reactions: Keith_McClary
Physics news on Phys.org
I'm not even close to a physicist, so if this needs to be and a different forum to get the best response feel free to clue me or move it where it needs to be. Thanks.
 
puc said:
Summary:: I asked NIK282K who watermarked the following one minute video if I could post it here to see if anyone might be able to say exactly what is happening and explain it. Yes was his answer.

So here it is. I took a guess but I couldn't really answer, hopefully you can.

Slow motion video of pulsations occurring while sucking liquid soap into a syringe.
Things like this happen if you have a combination of resistance and elasticity. Soap has long molecules and can build up some tension when stretched, so when the connections on one side are torn it is pulled back by those on the other side.
 
  • Like
Likes   Reactions: sophiecentaur
There is a vortex forming just behind where the soap is drawn into the syringe, along the metal.
When the liquid in front of the "syringe-hole" is pulled into the syringe it causes the soap behind the syringe hole to be pulled forwards.

Seems the phenomena would also be present in other liquids, but a lot harder to observer with a lack of bubbles.
 
  • Like
Likes   Reactions: anorlunda
A.T. said:
Things like this happen if you have a combination of resistance and elasticity. Soap has long molecules and can build up some tension when stretched, so when the connections on one side are torn it is pulled back by those on the other side.

There seem to be a lot of bubbles in the solution. These would give the bulk a lower modulus than a bubble free solution. It seems very much like the effect of vibrations in in the tube of a wind instrument only with, of course, different values for modulus and density (plus viscosity).

If the bubbles are in there to improve the visibility of the liquid flow then perhaps they could be replaced with small solid particles of neutral density. Also the number and size of bubbles could be varied.

Alternatively, it could be something to do with the driving mechanism not being decoupled properly or a springy tube.
 
sophiecentaur said:
Alternatively, it could be something to do with the driving mechanism not being decoupled properly or a springy tube.
The tube certainly moves around a lot, which makes the fluid do the same.
 
So we could be looking at an oscillator involving the mass of the syringe and the modulus of what is holding it OR the behaviour of a fairly compressible viscous liquid. Seems we need quite a bit more information about the setup before we could suggest anything useful.
 
Several hours ago I wrote the guy and included what has been offered here and suggested that more information would be needed. When I get a response I'll post again.

Thanks for all the replies. There will be updates.
 
From NIK282K

"Interesting replies, I'll have to do some more work and probably make a better setup.

I had thought of the long-ness of the soap molecules, this soap in particular can make threads ~0.5-1mm wide and up to 5mm long that slide around on a smooth soap surface.
------
Hadn't thought about vortexes!
------
the bubbles are there to help visibility BUT I did try again with completely clear soap and saw a similar effect in the index of refraction (the same tugging and jittering). I'll have to try again with some mica powder.

The syringe is fully retracted and held in place but I could probably do a better job at that.
------
I do have shaky hands but the frequency of the soap jitters is a lot faster.
------
Just off the top of my head. Lots to think about."
 
  • #10
Can you drive the piston with something stronger than by hand? If you use water with a much smaller hole, can you produce oscillations? I'm wondering if the syringe is the cause of the oscillations. Try a metal (more rigid) syringe?
So many things to eliminate - something to really get your teeth into.

Another idea. If you have an oscillation / resonance there will be a modulus and mass / density. Helmholtz Resonance? Measure the (change in) volume of the syringe under various loads to find the modulus.
 
  • #11
sophiecentaur said:
I'm wondering if the syringe is the cause of the oscillations.
I have definitely seen this: The before mentioned combination of resistance (friction at the syringe piston seal) and elasticity (plastic/rubber deformation) makes pulling a syringe jittery.
 
  • Like
Likes   Reactions: sophiecentaur
  • #12
A.T. said:
(plastic/rubber deformation) makes pulling a syringe jittery.
It wouldn't happen with a Gas Syringe, I'm sure. A gas syringe has strong glass sides and a cylindrical glass piston with a deep ground glass seal.
1598863828509.png
 
  • #13
I've relayed your responses
 
  • #14
And his reply.

"The piston is being drawn up its full length until there is a void between it and the soap entering at the bottom. At that point the force is dictated by the ambient air pressure forcing the soap into the tip. Until the volume is nearly full I'm pretty sure that the force is constant. Its one of the reasons they use vacuum cylinders on workout equipment in space (lighter than springs and its a constant force, unlike springs)."
 
  • #15
Oops. Apparently he didn't read your relayed responses before writing the above.
 
  • #17
I'm afraid there is a vital missing piece of evidence and that is the mechanical setup to drive the piston and to hold the syringe. It looks as though it's being held by someone because the needle jiggles about. That has to be sorted out. The syringe has to be clamped firmly and the force on the piston must be uniform and well defined. Without that, we have no idea where the oscillations are coming from.
 
  • #18
I passed your response on to the guy
 

Similar threads

Undergrad Blowing Bubbles in Space: Can You Create a Giant Bubble in the Vacuum of Space?
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad What is the equation for calculating average gas flow in a compressed syringe?
  • · Replies 9 ·
Replies
9
Views
2K
Calculating force on a syringe plunger for a viscous fluid?
  • · Replies 10 ·
Replies
10
Views
6K
Undergrad Fluid Dynamics - Pressure at the end of a syringe
  • · Replies 5 ·
Replies
5
Views
15K
Graduate Resonant frequencies of liquid in a cylinder
  • · Replies 14 ·
Replies
14
Views
2K
Will Dishwasher Liquid Affect Blood Samples?
  • · Replies 9 ·
Replies
9
Views
5K
Graduate Can Hamson-Linde cycle liquidize N2?
  • · Replies 7 ·
Replies
7
Views
3K
IBDP Extended Essay Ideas -- Help please
  • · Replies 2 ·
Replies
2
Views
2K
Can alcohol (ethanol) remove or destroy dishwasher liqiud?
  • · Replies 1 ·
Replies
1
Views
4K
Undergrad How to find the change in volume of a solid to a liquid
  • · Replies 3 ·
Replies
3
Views
1K