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HyperPhysics - Poiseuille's Law

PY105Notes - Viscosity and surface tension
Basic overview discussion of viscosity, Poiseuille's equation, and Surface Tension.

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Special points of emphasis

Work, Energy, and Power

Fluid Mechanics

When you think about energy in fluid mechanics, the two laws you should have foremost in mind are Bernoulli's Law and Pouseuille's Law.

Berneoulli's Law describes the ideal case, conservation of energy in a fluid that flows without friction, a fluid with no viscosity, or internal friction.

Pouseuille's Law describes the dissipation of energy as a real fluid encounters the friction of the pipe.

Both laws have appeared on many MCATs, although with Pouseuille's Law, the passage is more likely to give you an orientation than in a passage dealing with Bernoulli's. With Bernoulli's Law, you are more likely to be expected to reason conceptually without being given the formula.

Bernoulli's is higher on the scale of required knowledge. Pouseuille's Law is the kind of thing that shows up a lot, but the exam would likely present the formula and a short discussion within the passage.

Fluid Mechanics

The Cardiovascular System

A favorite theme on the MCAT for Pouseuille's Law is to see if you understand that because of the extreme effect of decreasing radius on viscous dissipation, the pressure drop per unit length in narrow vessels is much greater than in larger vessels.

From an MCAT writer's perspective, this is the type of concept which you can create an interesting set of answers to a multiple choice question. Furthermore, this consequence of Pouseille's Law is relevant to future doctors. In the cardiovascular system, a major consequence is that the narrow vessels must be much shorter.

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