It has been believed that water and silicon oil are Newtonian fluids. But recently it was found that both the fluids do not always fit the result of numerical calculation obtained using Navier-Stokes equation for the pressure drop in the flow through very small orifices. In the present study, the author measures the reaction force and the diameter of jets of water and silicon oil issuing from small orifices and examines the possibility of elasticity in these fluids. The measured values are compared with the numerical values calculated using N-S equation. The result shows that silicon oil of 30 centistokes of kinematic viscosity gives the data consistent with the numerically obtained data but water gives the characteristic of viscoelastic fluids; the reaction force is smaller than the numerically calculated value and the measured diameter of jet is larger than the value predicted with N-S equation. Then water is regarded as viscoelastic fluids and the elastic stress is estimated.

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