# 018 — Sling Force

## Problem Situation

When riggers set up a two-leg sling, the included angle between the sling legs invisibly multiplies the tension in each leg. At 60° the multiplier is modest (1.15×), but at 120° each leg carries the full load weight (2.00×), and at 150° the tension is nearly 4× the straight-pull force. This non-linear spike kills people — 30% of rigging accidents involve incorrect sling usage. Riggers use lookup tables and charts, but numbers don't build intuition. You can know that 120° = 2× and still not feel the danger, because the relationship between "moderate-looking angle" and "catastrophic force" is invisible.

## What Was Built

A live force-geometry instrument. A beam sits at the top, a load hangs below, and two sling legs connect them. Drag the attachment points to change the angle. Force vectors are drawn at the load point — arrows along the sling directions whose length represents actual tension. As the angle widens, the load rises (constant sling length), the vectors grow non-linearly, and the color shifts from gray (SAFE) through amber (CAUTION) to red (DANGER). A radial glow appears in the danger zone. A small force-angle curve shows the full TF relationship with the current position marked.

## Why This Form

The force vector triangle IS the physics. In a two-leg sling, the equilibrium condition is literally a triangle of forces — the weight pulling down, the two sling tensions pulling up along the sling legs. Drawing that triangle and letting the user manipulate it makes the invisible force multiplication visible in its native geometric form. This is not a metaphor or a design choice — it's the actual force diagram from statics.

## What Is Actually Interesting

The non-linear spike. At small angles, the force vectors grow slowly — you feel safe. Then somewhere past 90° the vectors start accelerating, and by 120° they've doubled, and by 145° they're enormous red arrows shooting sideways. The load rising up toward the beam as the angle widens adds a second visceral cue: the geometry itself looks increasingly wrong. The moment of understanding — "oh, the force doesn't grow linearly" — is the whole point, and it can only be felt through continuous interaction, not from a chart.

## Iterations

No v1.1. The first version hit the core move cleanly.

## Next Step

Add a sling rating overlay — let the user input a sling's rated capacity and see the exact angle where it exceeds that rating. This would turn the diagnostic instrument into an operational planning tool.

## Art Direction

Dark editorial treatment. Monochrome-first with color used structurally: gray for safe, amber for caution, red for danger. Geist for readouts, JetBrains Mono for labels and values. Generous negative space below the rising load point reinforces the geometry. The empty space IS the signal — as the load rises and the space disappears, danger increases.

## Promotion Candidate Read

Maybe. The form-to-problem fit is mathematically native — the force vector triangle IS the physics, not a visualization metaphor. The non-linear force spike is a genuine revelation when felt interactively vs. read from a table. But the audience is narrow (riggers, stage hands, construction workers), and the instrument is currently diagnostic-only. It would need operational features (sling ratings, multi-leg configurations, load factor presets) to graduate.
