---
id: 587d78a9367417b2b2512aea
title: Make Motion More Natural Using a Bezier Curve
challengeType: 0
videoUrl: 'https://scrimba.com/c/c7akWUv'
---

## Description
<section id='description'>
This challenge animates an element to replicate the movement of a ball being juggled. Prior challenges covered the <code>linear</code> and <code>ease-out</code> cubic Bezier curves, however neither depicts the juggling movement accurately. You need to customize a Bezier curve for this.
The <code>animation-timing-function</code> automatically loops at every keyframe when the <code>animation-iteration-count</code> is set to infinite. Since there is a keyframe rule set in the middle of the animation duration (at <code>50%</code>), it results in two identical animation progressions at the upward and downward movement of the ball.
The following cubic Bezier curve simulates a juggling movement:
<code>cubic-bezier(0.3, 0.4, 0.5, 1.6); </code>
Notice that the value of y2 is larger than 1. Although the cubic Bezier curve is mapped on an 1 by 1 coordinate system, and it can only accept x values from 0 to 1, the y value can be set to numbers larger than one. This results in a bouncing movement that is ideal for simulating the juggling ball.
</section>

## Instructions
<section id='instructions'>
Change value of the <code>animation-timing-function</code> of the element with the id of <code>green</code> to a <code>cubic-bezier</code> function with x1, y1, x2, y2 values set respectively to 0.311, 0.441, 0.444, 1.649.
</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: The value of the <code>animation-timing-function</code> property for the element with the id <code>green</code> should be a <code>cubic-bezier</code> function with x1, y1, x2, y2 values as specified.
    testString: assert($('#green').css('animation-timing-function') == 'cubic-bezier(0.311, 0.441, 0.444, 1.649)', 'The value of the <code>animation-timing-function</code> property for the element with the id <code>green</code> should be a <code>cubic-bezier</code> function with x1, y1, x2, y2 values as specified.');

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='html-seed'>

```html
<style>
  .balls {
    border-radius: 50%;
    position: fixed;
    width: 50px;
    height: 50px;
    top: 60%;
    animation-name: jump;
    animation-duration: 2s;
    animation-iteration-count: infinite;
  }
  #red {
    background: red;
    left: 25%;
    animation-timing-function: linear;
  }
  #blue {
    background: blue;
    left: 50%;
    animation-timing-function: ease-out;
  }
  #green {
    background: green;
    left: 75%;
    animation-timing-function: cubic-bezier(0.69, 0.1, 1, 0.1);
  }

  @keyframes jump {
    50% {
      top: 10%;
    }
  }
</style>
<div class="balls" id="red"></div>
<div class="balls" id="blue"></div>
<div class="balls" id="green"></div>
```

</div>



</section>

## Solution
<section id='solution'>

```html
<style>
  .balls {
    border-radius: 50%;
    position: fixed;
    width: 50px;
    height: 50px;
    top: 60%;
    animation-name: jump;
    animation-duration: 2s;
    animation-iteration-count: infinite;
  }
  #red {
    background: red;
    left: 25%;
    animation-timing-function: linear;
  }
  #blue {
    background: blue;
    left: 50%;
    animation-timing-function: ease-out;
  }
  #green {
    background: green;
    left: 75%;
    animation-timing-function: cubic-bezier(0.311, 0.441, 0.444, 1.649);
  }

  @keyframes jump {
    50% {
      top: 10%;
    }
  }
</style>
<div class="balls" id="red"></div>
<div class="balls" id="blue"></div>
<div class="balls" id="green"></div>
```
</section>