# Family magnetic

## The contract in words, and how to choose

No hand-written part: how to choose among this family's laws, or to attach them together, is not written yet.

## Contract

What every member must satisfy, as the family's harness checks it on the member's own node.

- Sign rule: the field turns the body's moment toward it (tau . (m x B) is not negative), and its gradient pulls the moment up the gradient of its alignment (F . (G^T m) is not negative): an aligned moment is pulled toward the stronger field
- Cases a member passes: `sign`, `frame`, `units`, `material reach`, `oracle`, `gradients`, `nodes`
- Settings that stand for a material's properties, each of which must reach the output: `moment`
- Deliveries a two-way law makes equal and opposite: none
- Reference member a swap replaces: none
- Settings proportional to a material property: none

## Members

| Entry | Rung | Derivative |
|---|---|---|
| [`magnetic.force`](../entries/interaction/magnetic.force.md) 0.1.0 | none | `exact` |
| [`magnetic.torque`](../entries/interaction/magnetic.torque.md) 0.1.0 | none | `exact` |

## Comparison

The members of this family are not alternatives to one another, so they are not compared.