Conceptual question: Bernoulli's Principle Syringes

Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
3 replies · 3K views
bismuthman
Messages
3
Reaction score
0

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

 
Physics news on Phys.org
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!