Understanding pound-force-seconds per square foot to pounds per foot-second Conversion
The pound-force-second per square foot (lbf·s/ft²) is the force-based British Gravitational unit of dynamic viscosity. The pound per foot-second (lb/(ft·s)) is the mass-based English absolute unit. The two differ by standard gravity (about 32.174), because one uses pound-force and the other pound-mass; this conversion is common when reconciling gravitational and absolute English-unit fluid calculations.
Conversion Formula
To convert pound-force-seconds per square foot to pounds per foot-second, multiply by this factor:
Step-by-Step Example
Convert 25 pound-force-seconds per square foot to pounds per foot-second.
How to Convert pound-force-seconds per square foot to pounds per foot-second
Bridge force-based and mass-based English viscosity units.
- Take the lbf·s/ft² value: Record the viscosity in gravitational units.
- Multiply by 32.17405: This is standard gravity in ft/s², linking the two units.
- Report in lb/(ft·s): The product is the absolute-unit viscosity.
- Worked result: 25 lbf·s/ft² × 32.17405 = 804.351 lb/(ft·s).
pound-force-seconds per square foot to pounds per foot-second conversion table
| pound-force-seconds per square foot (lbf-s/ft2) | pounds per foot-second (lb/(ft-s)) |
|---|---|
| 0 | 0 |
| 1 | 32.17405 |
| 2 | 64.3481 |
| 3 | 96.52215 |
| 4 | 128.6962 |
| 5 | 160.8702 |
| 6 | 193.0443 |
| 7 | 225.2183 |
| 8 | 257.3924 |
| 9 | 289.5664 |
| 10 | 321.7405 |
| 15 | 482.6107 |
| 20 | 643.481 |
| 25 | 804.3512 |
| 30 | 965.2215 |
| 40 | 1286.962 |
| 50 | 1608.702 |
| 60 | 1930.443 |
| 70 | 2252.183 |
| 80 | 2573.924 |
| 90 | 2895.664 |
| 100 | 3217.405 |
| 150 | 4826.107 |
| 200 | 6434.81 |
| 250 | 8043.512 |
| 300 | 9652.215 |
| 400 | 12869.62 |
| 500 | 16087.02 |
| 600 | 19304.43 |
| 700 | 22521.83 |
| 800 | 25739.24 |
| 900 | 28956.64 |
| 1000 | 32174.05 |
| 2000 | 64348.1 |
| 3000 | 96522.15 |
| 4000 | 128696.2 |
| 5000 | 160870.2 |
| 10000 | 321740.5 |
| 25000 | 804351.2 |
| 50000 | 1608702 |
| 100000 | 3217405 |
| 250000 | 8043512 |
| 500000 | 16087020 |
| 1000000 | 32174050 |
What is the pound-force-second per square foot?
The pound-force-second per square foot (lbf·s/ft²) is the unit of dynamic (absolute) viscosity in the English/US customary gravitational system. It is sometimes called the "slug per foot-second" because it is numerically identical to that combination.
Definition
One pound-force-second per square foot is the viscosity that produces a shear stress of one pound-force per square foot at a shear rate of one per second:
The exact value follows from the definitions and , giving exactly. It equals one reyn's cousin in ft units, and is identical to .
Origin and History
The unit belongs to the foot-pound-second (FPS) gravitational system used by English-speaking engineers, in which force (the pound-force) rather than mass is a base concept. It became standard in aeronautical and mechanical engineering texts in the United States during the 20th century, where fluid properties were often tabulated in customary units.
Law and Notable Facts
It is not an SI unit; the SI equivalent is the pascal-second. A closely related unit, the reyn (1 lbf·s/in²), is used in lubrication engineering and equals , exactly 144 times the lbf·s/ft² because there are 144 square inches per square foot.
Real-World Examples and Conversions
Water at 20 °C, about , is roughly . Conversely, , a very viscous fluid comparable to thick syrup. Air at room temperature () is about .
What is the pound per foot-second?
The pound per foot-second (lb/(ft·s)) is a unit of dynamic (absolute) viscosity in the English absolute (mass-based) system, where the pound is treated as a unit of mass (pound-mass). It is the FPS analogue of the poise, which is the gram per centimetre-second.
Definition
One pound per foot-second is the viscosity of mass one pound-mass flowing through one foot per second:
The exact value comes from and , giving . This is the pound-mass form and must not be confused with the gravitational pound-force-second per square foot, which is about 32.174 times larger.
Origin and History
This unit arises from the English absolute (or "poundal") system of mechanics, in which mass is the base quantity and force is the derived poundal. It appears in older engineering and chemical-engineering literature, particularly British texts, as a direct mass-based counterpart to the CGS poise.
Law and Notable Facts
It is not an SI unit. A useful relationship: , and the difference between this mass-based unit and the force-based lbf·s/ft² is exactly the standard gravitational conversion factor (the ratio of pound-force to poundal).
Real-World Examples and Conversions
Water at 20 °C () is about . A fluid of is roughly as viscous as light honey. Motor oil around is about .
Frequently Asked Questions
How many pounds per foot-second equal one lbf·s/ft²?
One pound-force-second per square foot equals about 32.174 lb/(ft·s).
Why is the factor about 32.174?
It equals standard gravity in ft/s², which relates the force-based lbf·s/ft² to the mass-based pound per foot-second.
What factor converts lbf·s/ft² to pounds per foot-second?
Multiply the lbf·s/ft² value by 32.17405.
What is 3 lbf·s/ft² in pounds per foot-second?
3 lbf·s/ft² equals about 96.5222 lb/(ft·s) (3 × 32.17405).
When does this conversion matter?
It matters when a fluid problem mixes gravitational (lbf) and absolute (lbm) English units and the viscosity must be made consistent.
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Complete pound-force-seconds per square foot conversion table
| Unit | Result |
|---|---|
| pascal-seconds (Pa-s) | 47.88026 Pa-s |
| millipascal-seconds (mPa-s) | 47880.26 mPa-s |
| poises (P) | 478.8026 P |
| centipoises (cP) | 47880.26 cP |
| pounds per foot-second (lb/(ft-s)) | 32.17405 lb/(ft-s) |