Conceptual question: Bernoulli's Principle Syringes

AI Thread Summary
To empty two syringes with different needle diameters in the same time, the plunger force required will differ due to viscous pressure losses, which dominate over inertial pressure variations described by Bernoulli's principle. The syringe with the smaller diameter needle will experience greater resistance, requiring more force to achieve the same flow rate. The pressure on the walls of the syringes will vary, with higher pressure in the smaller needle due to increased viscosity effects. The speed of fluid exiting the syringes will also differ, with the larger diameter needle allowing for a faster flow rate. Understanding these principles is crucial for applying fluid dynamics in practical scenarios.
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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