8.2.4 Fluids in the Real World: Surface Tension, Turbulence, and Viscosity

Question 1

Fluids in the Real World: Surface Tension, Turbulence, and Viscosity

Answer 1

• Real fluids are not ideal, and therefore you cannot always describe them using the same equations as for ideal fluids.
• Surface tension causes the surface of a fluid to behave like a stretched membrane.
• Turbulence has characteristics opposite to those of laminar flow.
• Viscosity is a measure of how much friction exists between the molecules of a fluid

Question 2

Which of the following statements concerning surface tension is not correct?

Answer 2

Compared to most liquids, water has a high surface tension and its surface tension is not affected by differences in temperature.

Question 3

A spherical object of density 2.010^3 kg/m^3 and radius 2.0 mm falls through fluid of density 1.410^3 kg/m^3 and viscosity 510^-4 (Ns)/m^2. Find the terminal speed of the object, which is reached when Fd + B = W, where B is the buoyant force of the fluid and W is the weight of the sphere. Fd is the drag force.

Answer 3

10.4 m / s

Question 4

Stoke’s law can be used to determine _____________

Answer 4

the radius of small spherical-shaped objects falling through a real fluid with laminar flow

Question 5

Which of the following statements is not correct?

Answer 5

Viscosity is the ratio of the strain rate to the shear stress.

Question 6

Which of the following is incorrect?

Answer 6

A liquid supports shear stress, which is evident when you see bugs walking on water.

Question 7

Which of the following statements about real fluids or ideal fluids is not correct?

Answer 7

Surface tension, turbulence, and nonviscous flow are characteristics of real fluids.

Question 8

Fluid behavior that results from instabilities in laminar flow is called turbulent. Such flow is in a complex and disordered. Whether a flow is laminar or turbulent depends on several characteristics of the fluid and its environment. Which of the following is not one of those characteristics?

Answer 8

none of the above

Question 9

True or false?
A flow pattern that is irregular and changes continuously with time is called turbulent. Bernoulli’s equation, which relates pressure, flow speed and height of flow can be applied to this type of flow pattern.

Answer 9

false

Question 10

Consider a smooth sphere of radius r falling through air with a speed v. Assume that the flow in this case is laminar. Which of the following is correct?

Answer 10

For a sphere of radius r, the force of viscous drag is proportional to the velocity and is opposite to the direction of the velocity vector