# One kilogram at arm's length

Held 50 centimetres from the elbow, a one-kilogram object creates about 4.9 N·m of torque. The same object held 5 centimetres away creates 0.49 N·m.

## The idea

Distance makes the torque ten times larger. The equation is `τ = m × g × d × sin(θ)`, with `g = 9.80665 m/s²`.

## What you can explore

Move the mass, distance, angle and biceps moment arm. With the 3.8 cm reference at 90°, 4.9 N·m means about 129 N of equivalent force at the biceps insertion.

This is a static model. It leaves out forearm mass, movement, shoulder mechanics, hand rotation and the contribution of every elbow flexor.

## Sources

- [NASA Glenn Research Center, Torque (Moment)](https://www.grc.nasa.gov/www/k-12/airplane/torque.html)
- [Functional Consequence of Distal Brachioradialis Tendon Release](https://pmc.ncbi.nlm.nih.gov/articles/PMC3640432/)
- [Murray, Delp & Buchanan, Variation of muscle moment arms](https://doi.org/10.1016/0021-9290(94)00114-J)
- [Akagi et al., In vivo measurements of moment arm lengths](https://pubmed.ncbi.nlm.nih.gov/22431216/)