Calculating Shear Stress in a Fluid Mechanics Problem

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The discussion focuses on calculating shear stress in a fluid mechanics problem involving two cubes connected by a string over a pulley on an inclined plane. The incline is covered with a thin layer of oil, and the user seeks clarification on how to calculate the shear stress exerted by the fluid on the cube on the incline. It is explained that shear stress for a Newtonian fluid can be calculated using the equation τ = μ*v/z, where τ is shear stress, μ is viscosity, v is velocity, and z is the thickness of the fluid layer. The user is also reminded that kinematic viscosity must be converted to dynamic viscosity by multiplying it by the fluid's density. The conversation emphasizes understanding the relationship between shear stress and fluid motion, akin to friction.
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I'm working on a fluid mechanics problem and I am not too sure how to approach it. There is a system with an inclined plane and 2 cubes, one attached to the other via a massless string and run through a massless pulley. One cube is dangeling down the vertical edge and the other is on the incline. They both weigh the same amount. The incine is 30 degrees and the question asks to calculate the tension in the string and the terminal velocity of the cubes. The incline is covered with a thin 0.1mm thick layer of oil which has a density of 886kg/m^3 and a dynamic viscosity of 0.29N s/m^2. The information it gives me is that the cubes specific gravity is 2.7 and the side dimentions are 20cm. The oil distribution can be considered to be linear.

I have it set up as a classical mechanics question, but not having any previous experience in fluids, I need to know what kind of force the fluid wil make with the Cube on the incline. I figure that there will be a shear stress. I have No idea how to calculate this. The rest of the problem I know how to set up. Is this shear stress calculated as a constant and then treated like kinetic friction, or is it considered a force? If someone could just quicky give me a quick explination and an equation or two on how to claculate the force exerted by the fluid, that would be great.

Regards,

Nenad
 
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Viscosity = 256.94 Pas

Friction due to shear stress, F = 102776v

Cube mass, m = 21.6kg

m g (1 - Sin \theta) = 102776v
v = 4.0988ms-1
 
how did you get that viscosity? and the constant for the hear stress equation. If you could please expliain, I would really appreciate it.

Regards,

Nenad
 
You were given the kinematic viscosity, you need the simple viscosity, which is the kinematic viscosity multiplied by the density.

The shear shress equation is based on the definition of shear stress for a Newtonian fluid.
Tau = mu*v/z
 
so shear stress is in opposition to the motion, just like friction right. And could you also ezplain what the vriables are in the shar stress equation. I know the questions I'm asking are simplistic, but I need a definite answer. Thanks in advance.

Regards,

Nenad
 
Shear stress opposes relative motion in the fluid.

Tau = shear stress; mu = viscosity; v = velocity; z = thickness of layer.

Hope this helps.
 
thanks a lot speed. I really appreciate the help.

Regards,

Nenad
 
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