This page now isolates the Prony-brake force-arm rule and exact torque-unit conversions. A separate 1000-rpm reference shows P=T omega without implying that the entered force and arm describe a real rated brake.
Prony Force-Arm Rule Explorer
Enter declared perpendicular reaction force and arm length. The connected view preserves a stationary shoe and reaction arm around a prescribed rotating drum while the worksheet reports torque conversions and a clearly labeled 1000-rpm reference power.
Equation Used
- F and L are declared quantities and the force line is perpendicular to the arm.
- Torque-unit outputs are direct conversions of the same torque.
- Reference power uses exactly 1000 rpm and does not assert actual shaft speed.
- Drum motion is prescribed independently of the force-arm ledger.
- Calibration, zero, alignment, bearing drag, uncertainty, friction, heat transfer, cooling, wear, vibration, strength, capacity, guards, controls and safe operation are excluded.
Retains the exact perpendicular force-arm rule and unit conversions while removing unsupported thermal, performance, deployment and operating claims.
A reaction force at a perpendicular arm measures torque
Friction at the rotating drum tends to carry the brake assembly with it. A stationary arm transfers that moment to a force balance. When the force line is perpendicular to the arm, torque magnitude is exactly force times arm length.
The animation preserves that connected topology but does not solve friction or temperature.
Use this page only for force-arm and unit arithmetic
The worksheet calculates one declared torque, converts it to lbf·ft and lbf·in, and shows what ideal power that torque would correspond to at exactly 1000 rpm.
It cannot design, rate, calibrate, cool or authorize a brake or test rig.
Keep torque separate from the reference speed
The first identity needs only perpendicular force and arm length. Power additionally needs speed; 1000 rpm is explicitly a reference here.
A transparent force-arm example
For F=44.7 N perpendicular to L=0.38 m, torque is 16.99 N·m, 12.53 lbf·ft, or 150.34 lbf·in. At the separate 1000-rpm reference, ideal power would be 1.779 kW.
No actual brake operating point or rating follows.
The rule is not a complete measurement system
Real measurement requires verified perpendicular distance, force and speed calibration, simultaneous readings, zero and tare treatment, alignment, bearing-drag treatment and uncertainty analysis. Physical absorbers also require machine-specific thermal, structural and guarding controls.
The former accuracy, temperature, duration, cooling-flow, deployment, cost, maintenance and troubleshooting claims are removed.
Prony force-arm questions
Why is force perpendicular?
Otherwise the moment uses perpendicular distance or a vector cross product.
Is 1000 rpm an input?
No; it is a labeled reference.
Does the calculator predict friction or heat?
No.
Can it size a real brake?
No.
Prony force-arm references
- IIT Madras NPTEL, Mechanical Measurements, Example 17: spring-balance force, torque arm and power relation.
- Penn State ME 345 Mechanical Measurement Lab: measured arm, force, speed, torque and power workflow.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
