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Question
Modulus of rigidity of ideal liquids is ______.
Options
infinity.
zero.
unity.
some finite small non-zero constant value.
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Solution
Modulus of rigidity of ideal liquids is zero.
Explanation:
Modulus of Rigidity: Within limits of proportionality, the ratio of tangential stress to the shearing strain is called the modulus of rigidity of the material of the body and is denoted by η
i.e. η = `"Shearing stress"/"Shearing strain"`
In this case, the shape of a body changes but its volume remains unchanged.
Consider a cube of material fixed at its lower face and acted upon by a tangential force F at its upper surface having area A.
Only solids can exhibit a shearing as these have a definite shape.
In liquids, η = 0
So, the frictional (viscous) force cannot exist in the case of an ideal fluid and since they cannot sustain shearing stress or tangential forces are zero, there is no stress developed.
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