This page now follows the drawn form (a) topology instead of treating the number of supporting falls as an arbitrary input. One continuous ideal cord runs from a fixed anchor, around the load-attached movable sheave, over a fixed direction-changing sheave and down to the hauling end.
Form (a) Ideal 2:1 Reeving Explorer
Enter a declared load and load lift. The connected view preserves the fixed anchor, continuous cord, movable sheave, fixed direction-changing sheave and hauling end while reporting the exact ideal 2:1 force, travel and work ledger.
Equation Used
- One end of one continuous cord is fixed overhead.
- The cord passes under one load-attached movable sheave and over one fixed direction-changing sheave to the hauling end.
- The two cord parts acting upward on the movable block have equal ideal tension T.
- The fixed upper sheave changes hauling direction but does not add a supporting part at the movable block.
- Cord and sheaves are massless, inextensible and frictionless in the ledger.
- Friction, bending loss, reeving detail, acceleration, shock, ratings, inspection, guarding and safe operation are excluded.
Locks the model to the depicted fixed 2:1 continuous-cord topology and removes arbitrary fall-count and generic-efficiency claims.
Form (a) has exactly two supporting cord parts
One end of the continuous cord is fixed overhead. The cord descends around the load-attached movable sheave, rises over a fixed upper sheave, and descends as the hauling end. The two cord parts meeting the movable block each contribute ideal tension T, so W=2T.
The upper fixed sheave changes pull direction; it does not create another supporting part at the moving block.
Use this page only for the depicted ideal reeving ledger
The worksheet reports ideal effort, hauling-rope travel and work closure for declared load and lift. It cannot select, rate, inspect or authorize rope, sheaves, anchors, hooks, structure or a lifting operation.
Two-to-one force advantage requires two-to-one rope travel
Actual effort is greater in a real system because the rope bends and rubs and the sheaves and bearings have friction.
A transparent form (a) 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 output and input work are both 1000.00 J.
No component rating or safe working load follows.
The fixed 2:1 identity is not an actual capacity
Official Army and Navy guidance counts rope parts at the movable or traveling block and distinguishes theoretical from actual advantage because friction reduces performance.
The former arbitrary supporting-falls selector, generic efficiency factor, per-sheave loss claims, capacity advice, deployments, sizing rules, maintenance and troubleshooting claims are removed.
Form (a) reeving questions
Why is the mechanical advantage fixed at 2?
Exactly two cord parts act upward on the movable block.
Does the fixed upper sheave increase advantage?
No; it changes hauling direction.
Why must the hauling end move twice as far?
Both supporting parts shorten by the load lift h.
Can this size lifting hardware?
No.
Movable-pulley references
- US Army TC 4-13.17, Block and Tackle: theoretical advantage is found by counting parts of the falls at the movable block.
- US Navy Salvage Manual, Volume 1: supporting tensions sum at the traveling block and actual advantage is lower than theoretical because of friction.
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