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# spring(response:dampingFraction:blendDuration:)

A persistent spring animation. When mixed with other `spring()`
or `interactiveSpring()` animations on the same property, each
animation will be replaced by their successor, preserving
velocity from one animation to the next. Optionally blends the
response values between springs over a time period.

```
static func spring(response: Double = 0.5, dampingFraction: Double = 0.825, blendDuration: TimeInterval = 0) -> Animation
```

## Parameters

`response`

The stiffness of the spring, defined as an
approximate duration in seconds. A value of zero requests
an infinitely-stiff spring, suitable for driving
interactive animations.

`dampingFraction`

The amount of drag applied to the value
being animated, as a fraction of an estimate of amount
needed to produce critical damping.

`blendDuration`

The duration in seconds over which to
interpolate changes to the response value of the spring.

## Return Value

a spring animation.

---

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