Conceptual question: Bernoulli's Principle Syringes

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SUMMARY

The discussion centers on the application of Bernoulli's Principle to a scenario involving two syringes with different needle diameters, both containing the same volume of water. It concludes that Bernoulli's Principle is not applicable due to the dominance of viscous pressure losses in the fluid flow, particularly in the smaller diameter needle. The conversation highlights the importance of understanding laminar viscous flow and its effects on fluid dynamics, especially in scenarios involving narrow passages.

PREREQUISITES
  • Understanding of Bernoulli's Principle
  • Knowledge of viscous flow and its characteristics
  • Familiarity with laminar and turbulent flow distinctions
  • Basic principles of fluid mechanics
NEXT STEPS
  • Study the principles of laminar viscous flow in tubes
  • Explore the effects of needle diameter on fluid dynamics
  • Learn about pressure loss in fluid systems due to viscosity
  • Investigate the relationship between flow rate and pressure in syringes
USEFUL FOR

Students preparing for the MCAT, physics enthusiasts, and anyone interested in fluid dynamics and the principles governing syringe operation.

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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