This page now makes the ideal tackle assumptions explicit: the selected count is the number of rope parts acting on the movable block, every part has equal tension, and friction is excluded. The connected animation shows the movable block, load, supporting parts and hauling end together.
Ideal Block-and-Tackle Explorer
Enter a declared load, number of supporting rope parts at the movable block, and lift height. The connected view reports ideal effort, hauling-rope travel, and the equal ideal input/output work ledger.
Equation Used
- n is the count of rope parts acting upward on the movable block.
- Every supporting part has the same ideal tension T.
- The hauling effort equals segment tension and W=nT.
- Lifting the movable block by h requires ideal hauling-rope travel s=nh.
- Blocks, sheaves, rope and attachments are massless and frictionless in the ledger.
- Rope stretch, sheave and bearing friction, fleet angle, reeving details, acceleration, shock, component ratings, inspection, guarding and safe operation are excluded.
Clarifies that n counts supporting rope parts at the movable block and adds exact ideal force, travel and work closure without implying actual efficiency or capacity.
Count the rope parts acting on the movable block
The US Army cargo-handling manual defines tackle mechanical advantage by counting the parts of the falls at the movable block. With ideal equal tension, each supporting part contributes one tension T, so n parts support load W=nT.
The connected animation keeps the load attached to the moving block and shows the selected supporting-part count.
Use this page only for the theoretical ledger
The worksheet calculates ideal effort, hauling-rope travel and equal input/output work for declared W, n and h.
It cannot select, rate, inspect or authorize any rope, block, hook, anchor, hoist or lifting operation.
Force advantage trades directly for rope travel
Real effort is greater because ropes bend and rub and sheaves and bearings have friction; actual values require the specific reeving and equipment data.
A transparent ideal-tackle example
For W=1000 N, n=2 and h=1 m, ideal 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.
Theoretical advantage is not actual capacity
US Army and Navy guidance distinguish theoretical from actual mechanical advantage because rope and sheave friction reduce performance. Real lifting also requires engineered, rated and inspected components and verified attachment structures.
The former generic usage, capacity, efficiency, sizing, cost, maintenance and troubleshooting claims are removed.
Block-and-tackle questions
What does n count?
The ideal rope parts acting on the movable block, not simply the number of pulleys.
Why does rope travel increase?
Every supporting part shortens by the load lift h.
Is effort really W/n?
Only in the ideal frictionless equal-tension ledger.
Can this select lifting hardware?
No.
Block-and-tackle references
- US Army TC 4-13.17, Block and Tackle: mechanical advantage from the parts of the falls at the movable block and load divided by mechanical advantage for theoretical effort.
- US Navy Salvage Manual, Volume 1: supporting rope tensions sum at the traveling block; theoretical advantage equals supporting-part count; actual advantage is lower because of friction.
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