# Family toy

## 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: toy.body.load on the body opposes toy.body.velocity of the body
- Cases a member passes: `sign`, `frame`, `units`, `material reach`, `oracle`, `gradients`, `swap`, `nodes`
- Settings that stand for a material's properties, each of which must reach the output: `c`
- Deliveries a two-way law makes equal and opposite: none
- Reference member a swap replaces: toy.drag 0.2.0, rung linear
- Settings proportional to a material property: none

## Members

| Entry | Rung | Derivative |
|---|---|---|
| [`toy.drag`](../entries/interaction/toy.drag.md) 0.2.0 | [`linear`](../entries/interaction/toy.drag.md#rung-linear) | `exact` |
| [`toy.drag`](../entries/interaction/toy.drag.md) 0.2.0 | [`quadratic`](../entries/interaction/toy.drag.md#rung-quadratic) | `exact` |

## Comparison

| Member | Validity | Checked against | Cost | Derivative | Needs a GPU |
|---|---|---|---|---|---|
| [`toy.drag linear`](../entries/interaction/toy.drag.md) | none declared | not measured | not measured | `exact` | not measured |
| [`toy.drag quadratic`](../entries/interaction/toy.drag.md) | none declared | not measured | not measured | `exact` | not measured |

A cell reads `not measured` until a measurement record or a claim holds it, and each is counted.