# Single movable pulley (power half the weight)

> Why does a movable pulley halve the effort?

- Category: Mechanisms › Pulleys and tackle
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 13 (1868)
- Page: https://xemstudio.com/objects/single-movable-pulley-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=single-movable-pulley-mechanism · Plain text: https://xemstudio.com/objects/single-movable-pulley-mechanism/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- The weight hangs from a pulley that rides in a bight of the rope: two strands hold it up, so each carries half the weight (P = W/2), and the free end moves twice as far as the weight.
- Here the rope's standing end plugs into the beam 15 mm left of centre, runs under a pitch-Ø30 sheave in the movable block and up to the hand; the Ø40 × 40 weight hangs from the block's stem.
- Brown's No. 13.
- Parts (each has its own page): tackle-beam-240-sockets, tackle-block-15-bottom-stem, rope-sheave-3mm-pitch-30, ropes-3mm-single-movable-pulley, tackle-weight-d40x40-socket, dowel-pins-metric.
- Brown's movement No. 13 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| sheave | pitch Ø30 (Ø3 rope) |
| mechanical advantage | 2 |
| hand travel / weight travel | 2 |

## Where the files are

- Henry T. Brown (1868, public domain): [Five Hundred and Seven Mechanical Movements — scan on archive.org](https://archive.org/details/fivehundredseven00browiala) — web — Publisher's page; dimensions are facts
- 507movements.com: [Brown's movement No. 13: figure, his text and an animation](https://507movements.com/mm_013.html) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/single-movable-pulley-mechanism/index.json · license: https://xemstudio.com/files/hardware/single-movable-pulley-mechanism/LICENSE.md

- single-movable-pulley-mechanism-assembly: [STEP](https://xemstudio.com/files/hardware/single-movable-pulley-mechanism/single-movable-pulley-mechanism-assembly.step) · [STL](https://xemstudio.com/files/hardware/single-movable-pulley-mechanism/single-movable-pulley-mechanism-assembly.stl) — Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)

## Questions

**Why does a movable pulley halve the effort?**

The weight hangs from a pulley that rides in a bight of the rope: two strands hold it up, so each carries half the weight (P = W/2), and the free end moves twice as far as the weight.

## Fits with

- [Tackle beam 240 × 20 × 12 with Ø3 sockets every 5 mm](https://xemstudio.com/objects/tackle-beam-240-sockets/)
- [Single block for a pitch-Ø30 sheave, stem down (movable block or floor block)](https://xemstudio.com/objects/tackle-block-15-bottom-stem/)
- [Rope sheave for Ø3 rope, pitch Ø30 (rope centre), Ø34.4 rim, Ø4 bore](https://xemstudio.com/objects/rope-sheave-3mm-pitch-30/)
- [Ø3 rope for the single movable pulley (drawn in place)](https://xemstudio.com/objects/ropes-3mm-single-movable-pulley/)
- [Weight Ø40 × 40 with a Ø3 top socket (394.58 g in steel)](https://xemstudio.com/objects/tackle-weight-d40x40-socket/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)