**Exploring Advanced Motion in CSS: The Power of the linear() Timing Function**
When animating elements on the web, the way an object transitions from one state to another is defined by a timing function. Traditionally, web developers have relied on Bézier curves for this purpose, using preset functions like `ease-in`, `ease-in-out`, or simply `ease`. Each of these presets creates a different "feel" to the animation, as they interpolate the movement between the start and end points in subtly distinct ways. The effect of these differences is easily seen when, for example, several circles move side-to-side over the same duration but appear to move very differently depending on the chosen timing function.
**Limitations of Bézier Curves**
Bézier curves are a versatile and widely adopted tool in CSS animations, but they have their limits. Specifically, they struggle to accurately simulate more complex, physics-based motions such as "spring" or "bounce" effects. For years, developers who wanted these richer motion styles had to turn to JavaScript libraries. However, JavaScript-driven animations often run on the browser's main thread, which can cause performance issues if the application is busy with other tasks.
**Introducing the linear() Timing Function**
Modern CSS now offers a new solution: the `linear()` timing function. Unlike the traditional `linear` preset (which maintains a constant speed), `linear()` is a much more powerful and flexible tool. It allows developers to model complex motion by describing the movement as a series of straight lines between specified points, rather than as a single mathematical curve.
While the name "linear()" might seem confusing at first—especially since there's also a preset called `linear`—the distinction is important. The `linear()` function with parentheses allows you to define a custom easing curve by specifying a series of points on a graph, with 0 representing the start and 1 the end of the transition. These points can be spaced evenly or assigned specific percentages of the animation's duration for even more control.
**Emulating Springs and Bounces in CSS**
One particularly exciting use of `linear()` is to replicate the feel of spring-based or bouncy animations, previously only possible with JavaScript. By feeding a sequence of progress values (and optionally, time percentages) into `linear()`, you can create effects where elements overshoot their target and settle back—just like a real spring.
However, generating believable spring or bounce curves by hand is challenging. Simple attempts using a small number of points tend to look stiff and unnatural. The solution is to use more data points—often 40 or more—for smoother, more convincing motion. Thankfully, tools like the [Linear() Easing Generator](https://linear-easing-generator.netlify.app/) and [Easing Wizard](https://easings.netlify.app/) have emerged. These tools let developers generate complex `linear()` strings based on physics parameters or even convert JavaScript-based timing functions into CSS-friendly formats.