SwiftUI .smooth
Bounce 0 means a critically damped spring: the fastest settle with no overshoot. Stiffness 157.91, damping 25.13 and mass 1 give a damping ratio of 1, so the spring is about critically damped. It settles to within 0.1% in 0.735 s. It never passes the end value.
Demo
Both boxes take 0.735 s. Playing at 0.5× speed.
Your system asks for reduced motion, so nothing plays. The chart shows the whole move.
Code
A spring has no fixed duration, so the CSS takes the settle time (735 ms) and a linear() string that follows the spring.
transition: translate 735ms linear(0, 0.0062, 0.0229, 0.0478, 0.0789, 0.1145, 0.1533, 0.1942, 0.2362, 0.2786, 0.3209, 0.3625, 0.4031, 0.4425, 0.4804, 0.5166, 0.5511, 0.5838, 0.6148, 0.6439, 0.6713, 0.6969, 0.7208, 0.7432, 0.764, 0.7833, 0.8012, 0.8177, 0.8331, 0.8472, 0.8603, 0.8723, 0.8833, 0.8935, 0.9028, 0.9114, 0.9193, 0.9265, 0.933, 0.9391, 0.9446, 0.9496, 0.9542, 0.9584, 0.9622, 0.9657, 0.9689, 0.9718, 0.9744, 0.9768, 0.9789, 0.9809, 0.9827, 0.9843, 0.9858, 0.9872, 0.9884, 0.9895, 0.9905, 0.9914, 0.9922, 0.993, 0.9937, 0.9943, 0.9948, 0.9953, 0.9958, 0.9962, 0.9966, 0.9969, 0.9972, 0.9975, 0.9977, 0.9979, 0.9981, 0.9983, 0.9985, 0.9986, 0.9988, 0.9989, 1);el.animate({ translate: ['0 0', '240px 0'] }, { duration: 735, easing: 'linear(0, 0.0062, 0.0229, 0.0478, 0.0789, 0.1145, 0.1533, 0.1942, 0.2362, 0.2786, 0.3209, 0.3625, 0.4031, 0.4425, 0.4804, 0.5166, 0.5511, 0.5838, 0.6148, 0.6439, 0.6713, 0.6969, 0.7208, 0.7432, 0.764, 0.7833, 0.8012, 0.8177, 0.8331, 0.8472, 0.8603, 0.8723, 0.8833, 0.8935, 0.9028, 0.9114, 0.9193, 0.9265, 0.933, 0.9391, 0.9446, 0.9496, 0.9542, 0.9584, 0.9622, 0.9657, 0.9689, 0.9718, 0.9744, 0.9768, 0.9789, 0.9809, 0.9827, 0.9843, 0.9858, 0.9872, 0.9884, 0.9895, 0.9905, 0.9914, 0.9922, 0.993, 0.9937, 0.9943, 0.9948, 0.9953, 0.9958, 0.9962, 0.9966, 0.9969, 0.9972, 0.9975, 0.9977, 0.9979, 0.9981, 0.9983, 0.9985, 0.9986, 0.9988, 0.9989, 1)', fill: 'both' });import { spring, springDuration, springLinear } from '../../core/motion/springs.js';
const k = 157.91, d = 25.13;
// per-frame code (window.seek, vawe.onFrame): t is seconds since the move starts
const x = 240 * spring(t, k, d);
// CSS and Web Animations: 735 ms, the linear() string above
el.animate(
{ translate: ['0 0', '240px 0'] },
{ duration: springDuration(k, d) * 1000, easing: springLinear(k, d), fill: 'both' },
);Numbers
- Stiffness
- 157.91k, with mass 1
- Damping
- 25.13d, with mass 1
- Damping ratio
- 1about critically damped
- Settle time
- 0.735 swithin 0.1% of the end
- Overshoot
- 0%stays inside the end
- Crosses the end
- 0times
- 50% of travel
- 0.134 s18% of the settle time
- 90% of travel
- 0.31 s42% of the settle time
- Natural frequency
- 12.57 rad/ssqrt(k)
- Ring period
- 35.816 sone swing of the overshoot
- Peak speed
- 3.39xtimes the average speed
- linear() points
- 81within 0.15% of travel
Computed with spring() and springDuration() from core/motion/springs.js. The settle time is the last moment the spring is more than 0.1% away from the end value; a library stops its own spring by its own rest thresholds, so its clock can run shorter.
Source of the numbers
| SwiftUI | SwiftUI documentation read on 2026-11-03 |
| .smooth: duration 0.5, bounce 0 (Apple: "no bounce") | Animation.smooth |
Read it at developer.apple.com/documentation/swiftui/animation/smooth.
Conversion: stiffness = (2 pi / response)^2, damping = 4 pi x dampingFraction / response, with mass 1. The duration-and-bounce forms map to response = duration and dampingFraction = 1 - bounce, the same bounce mapping Motion documents "as SwiftUI does". Apple states bounce 0 is critically damped and bounce 1 is undamped.
Related springs
The four closest curves in this set, by the average gap between the two springs over their first seconds. A gap of 0.01 is invisible; 0.1 is a different feel.