# SpringMass

> SpringMotion::new(stiffness, mass, x0, seconds) lets a block go from rest x0 meters from its rest position, and SpringMotion::damped(stiffness, mass…

Page: https://fframes-kit.pages.dev/docs/physics/spring-mass/
Cargo feature: `physics` (`fframes-kit = { version = "..", features = ["physics"] }`)

`SpringMotion::new(stiffness, mass, x0, seconds)` lets a block go from rest `x0` meters from
its rest position, and `SpringMotion::damped(stiffness, mass, damping, x0, seconds)` adds
friction. `SpringMass` draws the block on a spring from a wall. With `plot` set to the map of
axes you show (time along x, displacement up y), the displacement so far draws on them with
a dot at the current value, so the block and its graph move together. `trace(until,
per_second)` gives the same points for a plot of your own. Gallery scene: `SpringMass`.

Gallery clip of `SpringMass`: https://fframes-kit.pages.dev/media/scenes/SpringMass-0339f9ad.mp4

```rust
use std::sync::OnceLock;

use fframes_kit::prelude::*;

fn figure<'a>(ui: &mut Ui<'a, '_, '_>) -> Svgr<'a> {
    static MOTION: OnceLock<SpringMotion> = OnceLock::new();
    let motion = MOTION.get_or_init(|| SpringMotion::damped(20.0, 1.0, 0.6, 1.0, 6.0));
    let axes = Axes {
        x_range: Range::new(0.0, 6.0, 1.0),
        y_range: Range::new(-1.0, 1.0, 0.5),
        x_length: 9.0,
        y_length: 2.6,
        center: (0.0, -2.0),
        tips: false,
        ..ui.defaults()
    };
    let spring = ui.show(SpringMass {
        motion: Some(motion),
        wall: (-5.5, 1.6),
        rest_length: 3.5,
        plot: Some(axes.map(ui)),
        ..ui.defaults()
    });
    let axes = ui.show(axes);
    svgr!(<g>{axes}{spring}</g>)
}
```

## API

Components are plain structs. Set the fields you need and fill the rest with `..ui.defaults()`: the defaults below come from the current theme (`theme.` values are fields of `Theme`).

### SpringMass

| Field | Type | Default | Description |
| --- | --- | --- | --- |
| `motion` | `Option<&SpringMotion>` | `None` | The simulated oscillation to draw, built once in the video's constructor; `None` draws nothing. |
| `wall` | `(f64, f64)` | `(-6.0, 1.5)` | Where the spring is fixed to the wall (the middle of its end), in units of `ui.space`. |
| `rest_length` | `f64` | `3.0` | Meters from the wall to the block's near side at rest; the dashed line marks it. |
| `scale` | `f64` | `1.0` | Units of `ui.space` per meter. |
| `delay` | `f32` | `0.0` | Seconds after the local start before the block is let go. |
| `time_scale` | `f32` | `1.0` | Speed of the motion over local time; 2 runs twice as fast, 1 is real time. |
| `coils` | `usize` | `10` | Number of turns of the zigzag that draws the spring. |
| `block_size` | `f32` | `110.0` | Side of the square block in pixels. |
| `plot` | `Option<AxesMap>` | `None` | Axes to plot the displacement on as the block moves (time in seconds along x, meters along y); `None` for no plot. Draw the axes yourself. |
| `color` | `Color` | `theme.colors.text` | Colour of the spring, the wall and the floor. |
| `block_color` | `Color` | `theme.colors.accent` | Colour of the block. |
| `plot_color` | `Color` | `theme.colors.highlight` | Colour of the displacement plot and its dot. |
| `guide_color` | `Color` | `theme.colors.muted` | Colour of the dashed rest line. |
| `stroke_width` | `f32` | `theme.stroke.regular` | Width of the spring, the wall, the floor and the plot in pixels. |
| `enter` | `Option<EnterAnim>` | `None` | How the wall, floor and rest line draw in; `None` shows them from the start. |
| `exit` | `Option<ExitAnim>` | `None` | How the wall, floor and rest line leave at the end of the container; `None` stays. |
| `parts_enter` | `Option<FadeIn>` | `None` | How the spring, block and plot fade in; `None` for none. |
| `parts_exit` | `Option<FadeOut>` | `None` | How the spring, block and plot fade out before the end; `None` for none. |

Feature `physics` · [Source](https://github.com/khanhthanhdev/fframes-kit/blob/main/fframes-kit/src/kits/physics/spring.rs#L93)