Equations · equation
Newtonian Viscosity
Fluid Dynamics · 1687
- Equation
- τ = μ (du/dy)
- Field
- Fluid Dynamics
- Named After
- Isaac Newton
- Symbols
- τ shear stress in the fluid · μ dynamic viscosity, in pascal-seconds · du/dy the velocity gradient across the flow
- Year
- 1687
Significance
Newton's hypothesis of 1687: the drag between layers of a fluid sliding past one another is proportional to how fast the velocity changes across them, and the constant is the viscosity. Water's is a millipascal-second, honey's a few thousand times more, air's fifty times less. Fluids that obey it are Newtonian; paint, blood and mud are not, and their viscosity depends on how hard they are pushed.
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