Calculator inputs
Pick a method, enter values, then compute the viscous force and related outputs.
Formula used
1) Parallel plate shear
Shear rate: γ̇ = V / h
Shear stress: τ = μγ̇ = μ(V / h)
Force: F = τA = μAV / h
Use this when two surfaces move relative to each other across a thin, uniform fluid layer.
2) Known velocity gradient
Shear stress: τ = μ(dv/dy)
Force: F = τA = μA(dv/dy)
Use this when a local or average gradient is already available from testing or simulation.
3) Stokes drag
Drag force on a sphere: F = 6πμrv
Reynolds number check: Re = ρvD / μ
This is intended for creeping flow, usually when Reynolds number stays well below one.
4) Journal bearing film
Surface speed: V = πDN / 60
Area: A = πDL
Force: F = μA(V / c)
This is a thin-film engineering approximation for rotating shafts and sleeve bearings.
How to use this calculator
- Choose the engineering model that matches your geometry or test condition.
- Enter viscosity and the required dimensions in any supported unit.
- Set the desired output unit for the final force value.
- Click Calculate viscous force to show the result directly above the form.
- Review the derived metrics, notes, and the Plotly response graph.
- Use the CSV or PDF buttons to export the current calculation report.
Example data table
| Method | Viscosity | Geometry / Area | Velocity / Gradient | Gap / Clearance | Example force |
|---|---|---|---|---|---|
| Parallel plate shear | 0.85 Pa·s | 0.18 m² | 0.60 m/s | 0.002 m | 45.90 N |
| Known velocity gradient | 0.045 Pa·s | 0.75 m² | 120 1/s | — | 4.05 N |
| Stokes drag on sphere | 0.001 Pa·s | r = 0.015 m | 0.40 m/s | — | 0.000113 N |
| Journal bearing film | 0.12 Pa·s | D = 0.08 m, L = 0.10 m | 900 rpm | 0.0005 m | 22.74 N |
FAQs
1) What is viscous force?
Viscous force is the resisting force created by internal fluid friction. It appears when fluid layers move at different speeds or when an object moves through a fluid.
2) Which method should I choose?
Use parallel plates for thin sliding films, known gradient when dv/dy is available, Stokes drag for tiny spheres in creeping flow, and journal bearing film for rotating shaft lubrication estimates.
3) Why does the calculator ask for viscosity units?
Engineering data sheets often list viscosity in different unit systems. Unit selectors reduce conversion errors and let you use laboratory, catalog, or design-sheet values directly.
4) When is Stokes drag valid?
Stokes drag works best for very slow flow around small spheres, usually when the Reynolds number is below one. Above that range, inertial effects become important.
5) Does this calculator work for non-Newtonian fluids?
These formulas assume Newtonian behavior, where viscosity stays constant. For shear-thinning or shear-thickening fluids, use an apparent viscosity taken at the operating shear rate.
6) Why is force proportional to area?
Shear stress acts across the wetted surface. A larger area means the same stress is applied over more surface, so total viscous force increases linearly.
7) What does the Plotly graph show?
The graph shows how viscous force changes as the main driving variable increases, such as velocity, gradient, or shaft speed, while the other inputs stay fixed.
8) Can I use the exported files in reports?
Yes. The CSV file is useful for spreadsheets, while the PDF export is useful for project notes, design reviews, and engineering calculation records.