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Problem 2.56
[Difficulty: 2]
Given:
Flow between two plates
Find:
Force to move upper plate; Interface velocity
Solution:
The shear stress is the same throughout (the velocity gradients are linear, and the stresses in the fluid at the interface must be
equal and opposite).
Hence
τμ
1
du
1
dy
⋅
=
μ
2
du
2
dy
⋅
=
or
μ
1
V
i
h
1
⋅
μ
2
VV
i
−
()
h
2
⋅
=
where V
i
is the interface velocity

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