Bernoulli Principle

  • #1

Main Question or Discussion Point

I have read and understood the explanation of the Bernoulli principle based on conservation of energy, but what I would like is a more intuitive way of picturing just how the reduced pressure develops in, say, a venturi tube.

I want to be able to mentally track an element of the fluid and see, in my mind's eye, why a "slice" of the fluid flow presses on the walls with less and less pressure as it approaches the narrowest point. Is there an intuitive explanation of this sort?

Edit: I realized that I do not really understand it even in terms of conservation of energy. My problem is with dynamic energy : is it just the kinetic energy of an element?
 
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Answers and Replies

  • #2
LURCH
Science Advisor
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A description that helps em intuitively grasp the principle is the idea of representing the force of the fluid against an object (like the walls of a Ventury tube) as "arrows of force". If the fluid is sitting still, like perhaps still air at sea level, then the full force of 14lbs/in.2 is applied to the wall of the tube. You could picture the arrows of force pointing directly at the wall.

If the air is moving, the arrows point at an angle. On an airplane wing, these arrows would point at the bottom of the wing at a certain angle (depending on the forward motion of the wing), but they point at a shallower angle, indicating that the air only strikes a "glancing blow" against that side. Striking at a shallower angle means it applies less pressure, just like getting grazed by a fastball won't knock you backwards, while a direct hit could break a bone.
 

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