Conceptual question: Bernoulli's Principle Syringes

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Discussion Overview

The discussion revolves around the application of Bernoulli's principle to a scenario involving two syringes with different needle diameters, both filled with the same volume of water. Participants explore the forces and principles at play when attempting to empty both syringes in the same amount of time, focusing on pressure, force, and fluid dynamics.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions whether a greater force is required to empty the syringes in equal time, considering the different needle diameters.
  • Another participant suggests that Bernoulli's principle may not be applicable due to the dominance of viscous pressure losses in the flow through the small diameter needle.
  • A participant expresses a basic understanding of viscosity and seeks clarification on the concept of laminar viscous flow and its implications for fluid behavior in the syringes.

Areas of Agreement / Disagreement

There is no consensus on the applicability of Bernoulli's principle to this scenario, as one participant argues against its use while another seeks to understand the underlying principles involved.

Contextual Notes

The discussion highlights the potential limitations of applying Bernoulli's principle in scenarios dominated by viscous flow, as well as the need for a clearer understanding of fluid dynamics concepts such as laminar versus turbulent flow.

bismuthman
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Homework Statement



I'm interested in an explanation of the forces/principles involved in the following scenario: There are two syringes, level with one another, containing the same volume of water. The difference between the syringes is the gauge of the needle; one is of greater diameter than the other. One wishes to empty both syringes in the same amount of time.

Homework Equations



To empty the syringes in equal time, will one plunger require a greater force than the other?
How will the magnitude of the pressure on the walls of the two syringes vary?
How will the speed of the fluid exiting the syringe compare?
(Sort of vague) What can we learn by applying Bernoulli's principle to the problem?

Lastly:

Thanks you guys. I'm not very physics-minded and have been studying for the MCAT lately. I feel I should be able to understand any scenario in terms of the underlying principles. Not too realistic, but I'm especially interested in this one!


The Attempt at a Solution

 
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Hi Bismuthman. Welcome to Physics Forums.

This is not a problem that one would solve using Bernoulli. Because of the tiny diameter of the needle, the fluid flow in this system will be dominated by viscous pressure losses. The intertial pressure variations associated with Bernoulli will be negligible. Have you learned about viscous flow yet? If so, have you studied laminar viscous flow in a tube?

Chet
 
My understanding of viscosity is about as thick as a flashcard: the internal friction of a fluid, the resistance of the fluid to motion. I am aware of the distinction between laminar and turbulent flow. What exactly do you mean by laminar viscous flow? Am I to understand that the viscosity of the fluid increases in the needle of either syringe (moreso in the smaller of the two)?
 
Edit: Thanks for you answer!
 

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