# springForce

[Built-ins](README.md) · [Labs guide](../guides/labs.md)

Canonical ID: `physics.springForce`. Nederlands: `veerKracht`.

## Signature

```text
springForce(displacement, velocity, stiffness, damping)
```

Returns the signed restoring force `-stiffness * displacement - damping * velocity`
along your chosen axis. Displacement and velocity may be positive or negative;
stiffness must be positive and damping nonnegative. All values and the computed
force must be finite. The function does not move a body or advance a clock.

## Example

```pliro
# language: en
let force = springForce(0.5, 2, 120, 0.35)
say force # -60.7 N: upward if your axis points downward
```

For a trampoline, calculate compression during contact, apply this force to your
character's velocity, and record the same state in Labs. See the bundled
**Trampoline Lab** example. The spring never pulls a character downward if your
contact rule clamps tensile force to zero.