Venturi Effect Mcat

b) Buoyancy

Venturi Effect Mcat

The Venturi effect is the reduction in fluid pressure when a fluid flows through a constricted section. A pitot tube, a horizontal tube containing a U-shaped tube, is used to determine the velocity of a fluid flowing past it.

A pitot tube is a horizontal tube that contains a U-shaped tube. The surface of the pitot tube has at least two openings, one of which faces directly into the fluid flow. The first opening encounters fluid with a velocity of zero. The pressure at this opening is equal to the static pressure exerted by the fluid. The second opening encounters moving fluid. The pressure at this opening is equal to the total pressure exerted by the fluid. Each end of the U-tube is exposed to the pressure at just one of these openings, so the difference in fluid heights withing the U-tube can be used to calculate the differences in pressures according to ΔP=ρgΔh, where ρ is the density of the liquid. Because h₁=h₂ and v₁=0 m/s, Bernoulli’s equation can be simplified to

If the density of fluid is known, the difference in pressure measured by the U-tube can be used to determine the velocity of the fluid flowing past the pitot tube:

A Venturi tube is a horizontal tube with a constricted region – a region with decreased cross-sectional area – in its middle. A Venturi tube can be used to determine the velocity of a fluid that is flowing within it. This is in contrast to a pitot tube, which is used to determine the velocity of a fluid flowing past it. The continuity equation states that for a fluid with constant flow rate Q, a decrease in cross-sectional area A is associated with an increase in velocity v. Recall that Q = Av. Bernoulli’s equation states that for a fluid at a constant height, an increase in velocity is associated with a decrease in pressure.

The decrease in pressure occurs when a fluid flows into a constricted region of a pipe is known as the Venturi effect. A venturi meter can be sued to determine the velocity of a fluid in a pipe.

Practice Questions

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MCAT Official Prep (AAMC)

Practice Exam 2 C/P Section Question 25

Key Points

• A pitot tube is a horizontal tube that contains a U-shaped tube. It is used to determine the velocity of a fluid flowing past it.

• A Venturi tube is a horizontal tube with a constricted region – a region with decreased cross-sectional area – in its middle. A Venturi tube can be used to determine the velocity of a fluid that is flowing within it.

• The Venturi effect is the reduction in fluid pressure when a fluid flows through a constricted section.

Key Terms

Pitot tube: a flow measurement device used to measure fluid flow velocity based on Venturi effect. It is widely used to determine the airspeed of an aircraft, water speed of a boat, and to measure liquid, air and gas flow velocities in certain industrial applications.

Venturi tube: A horizontal tube with a constricted region – a region with decreased cross-sectional area – in its middle

Fluid density: The average density of a substance or object is defined as its mass per unit volume, ρ = m/ V.

Bernoulli’s equation: States that for a fluid at a constant height, an increase in velocity is associated with a decrease in pressure.

Venturi effect: The reduction in fluid pressure when a fluid flows through a constricted section.

Fluid Mechanics for the MCAT: Everything You Need to Know

Learn key MCAT concepts about fluid mechanics, plus practice questions and answers

(NOTE: THIS GUIDE IS PART OF OUR MCAT PHYSICS SERIES.)

Table of Contents

Part 1: Introduction to fluids

Part 2: Definition and applications

Part 3: Density, buoyancy, and applications of pressure

a) Density and specific gravity

b) Buoyancy

c) Hydrostatic pressure

d) Pressure and depth

Part 4: Fundamental laws

a) Pascal’s law

b) Poiseuille flow

c) Continuity equation

d) Bernoulli’s equation

Part 5: High-yield terms and equations

Part 6: Passage-based questions and answers

Part 7: Standalone questions and answers

Part 1: Introduction to fluids

As a study of substances including liquids, gases, and plasmas, the study of fluids is extremely important for a lot of real-world applications of physics, such as blood flow in the circulatory system.

This guide won’t necessarily follow a self-contained narrative from start to finish. Instead, we’ll start with a basic definition of fluids, which we’ll then combine with other physics intuitions to think about other implications. This unit should give you a comprehensive understanding of the fluid-related concepts you’ll see on the MCAT, as well as showing how concepts from other topics have implications everywhere!

On the MCAT, fluid mechanics is a medium-yield topic. Below, the most important terms are in bold font. When you see one, try to define it in your own words, and use it to create your own examples. This is a great way to check your understanding, and phrasing things in a way that makes the most sense to you will make studying much easier (and much more effective!) in the long run.

Part 2: Definition and applications

What is a fluid? You might know that fluids don’t only refer to liquids—other states of matter, like gases, are fluids as well. Let’s try to find a better definition of what a fluid is.

A fluid is a substance that will move under any shear stress. A shear stress is the result of a force that acts on the material from away from its center of mass.

When we place a fluid into a container (like water into a cup), the shear forces will continue to act on the fluid and shape it until it reaches an equilibrium.

We can classify the flow of fluids as laminar or turbulent. Think of the difference between a calm stream and a river with rapids. The former is slow and smooth; the latter is fast-moving and full of violent disturbances. This is generally the case with slow-moving and fast-moving fluids. Low-velocity fluids create laminar flow, and high-velocity fluids create turbulent flow.

In laminar flow, a slight disturbance is quickly corrected in an orderly manner, and in turbulent flow, a disturbance forms eddies and causes a much greater interruption.

You may also have noted the distinct spherical shapes that water droplets form, or the ability of water to “creep” up sheets of paper. Surface tension is a result of cohesion between the same type of molecules on the surface of the fluid. It allows the surface of a liquid to support light things, such as a leaf or an insect, which would otherwise sink.

Surface tension is also the reason water droplets form on a surface rather than covering the entire surface with an infinitesimal layer of liquid.