This page now follows the actual form (d) diagram: a fixed cord anchor, one load-attached movable sheave and one fixed upper redirect sheave for a downward hauling end. The two parts at the moving block fix the ideal ratio at 2:1.
Form (d) Ideal Fixed-Redirect 2:1 Explorer
Enter a declared load and load lift. The connected view preserves the anchor, two supporting parts, movable sheave/load, fixed redirect sheave and downward hauling end while reporting exact ideal force, travel and work closure.
Equation Used
- One cord end is fixed overhead.
- Exactly two cord parts act upward on the load-attached movable sheave.
- Both parts carry equal ideal tension T.
- The fixed upper sheave redirects the hauling end but adds no support at the moving block.
- Cord and sheaves are massless, inextensible and frictionless in the ledger.
- Friction, bending loss, acceleration, shock, ratings, inspection, guarding and safe operation are excluded.
Locks form (d) to the depicted fixed-anchor, movable-sheave and fixed-redirect two-part topology and removes arbitrary segment/efficiency controls.
Two cord parts support the moving block; the fixed sheave redirects the haul
The continuous cord runs from a fixed overhead anchor, under the load-attached movable sheave, over the fixed upper sheave and down to the hauling end. The two parts at the moving block each carry ideal tension T, so W=2T.
The fixed upper sheave changes hauling direction only.
Use this page only for the depicted ideal form (d) ledger
The worksheet reports ideal effort, hauling-rope travel and work closure for declared load and lift. It cannot select, rate, inspect or authorize a real lifting system.
The fixed-redirect topology retains a 2:1 ideal ratio
Real effort is higher because cord bending, sheave bearings and alignment introduce loss.
A transparent form (d) example
For W=1000 N and h=1 m, ideal hauling effort is 500.00 N and hauling-rope travel is 2.00 m. Ideal input and output work are both 1000.00 J.
No component rating follows.
Ideal force sharing is not actual capacity
Official Army and Navy guidance counts only rope parts acting on the movable or traveling block and distinguishes theoretical from actual advantage because friction reduces performance.
The former arbitrary segment and efficiency inputs, unsupported loss rates, capacity, human-effort, sizing, deployment, maintenance and troubleshooting claims are removed.
Form (d) questions
Does the fixed upper sheave add mechanical advantage?
No; it changes hauling direction.
Why is the ideal ratio fixed at 2:1?
Exactly two cord parts support the movable sheave.
Why is rope travel twice the lift?
Both supporting parts shorten by h.
Can this rate hardware?
No.
Movable-pulley references
- US Army TC 4-13.17, Block and Tackle: theoretical advantage is found by counting parts at the movable block.
- US Navy Salvage Manual, Volume 1: supporting tensions sum at the traveling block; actual advantage is lower because of friction.
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