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<!DOCTYPE html>

<!--
Code mostly taken from:
https://www.geeksforgeeks.org/multiple-pendulum-animation-using-css/
Unbelievable, geeksforgeeks actually producing quality content for once?

I adjusted the numbers based on this demo:
https://sciencedemonstrations.fas.harvard.edu/presentations/pendulum-waves
Also, the lengths are physically accurate (assuming pendulums obey simple harmonic motion which they pretty much do at small angles)
Technically, the angle should vary as a cosine function (assuming the small-angle approximation), but due to CSS limitations it's instead a linear function
Using a piecewise linear function for the animation would be more accurate, but no one can really tell the difference anyways
-->

<html>

<head>
    <title>
        Multiple Pendulum Animation using CSS
    </title>
    <style>
        *,
        *:before,
        *:after {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        /*.pendulum-base {
            width: 500px;
            height: 300px;
            margin: auto;
            border-top: 3px solid #66d63e;
        }*/

        .pendulum {
            position: absolute;
            right: 50%;
            transform: translate(-50%) rotate(20deg);
            width: 2px;
            height: calc(1000000px / 65 / 65);
            background: #b5ff9a;
            animation: moveIt calc(60s / 65) ease-in-out infinite;
            transform-origin: 50% 0;
        }

        .pendulum:nth-of-type(2) {
            height: calc(1000000px / 64 / 64);
            animation-duration: calc(60s / 64);
        }

        .pendulum:nth-of-type(3) {
            height: calc(1000000px / 63 / 63);
            animation-duration: calc(60s / 63);
        }

        .pendulum:nth-of-type(4) {
            height: calc(1000000px / 62 / 62);
            animation-duration: calc(60s / 62);
        }

        .pendulum:nth-of-type(5) {
            height: calc(1000000px / 61 / 61);
            animation-duration: calc(60s / 61);
        }

        .pendulum:nth-of-type(6) {
            height: calc(1000000px / 60 / 60);
            animation-duration: calc(60s / 60);
        }

        .pendulum:nth-of-type(7) {
            height: calc(1000000px / 59 / 59);
            animation-duration: calc(60s / 59);
        }

        .pendulum:nth-of-type(8) {
            height: calc(1000000px / 58 / 58);
            animation-duration: calc(60s / 58);
        }

        .pendulum:nth-of-type(9) {
            height: calc(1000000px / 57 / 57);
            animation-duration: calc(60s / 57);
        }

        .pendulum:nth-of-type(10) {
            height: calc(1000000px / 56 / 56);
            animation-duration: calc(60s / 56);
        }

        .pendulum:nth-of-type(11) {
            height: calc(1000000px / 55 / 55);
            animation-duration: calc(60s / 55);
        }

        .pendulum:nth-of-type(12) {
            height: calc(1000000px / 54 / 54);
            animation-duration: calc(60s / 54);
        }

        .pendulum:nth-of-type(13) {
            height: calc(1000000px / 53 / 53);
            animation-duration: calc(60s / 53);
        }

        .pendulum:nth-of-type(14) {
            height: calc(1000000px / 52 / 52);
            animation-duration: calc(60s / 52);
        }

        .pendulum:nth-of-type(15) {
            height: calc(1000000px / 51 / 51);
            animation-duration: calc(60s / 51);
        }

        @keyframes moveIt {

            0%,
            100% {
                transform: translate(-50%) rotate(30deg);
            }

            50% {
                transform: translate(-50%) rotate(-30deg);
            }
        }

        .pendulum:before {
            content: "";
            position: absolute;
            border-radius: 50%;
            transform: translate(-50%);
            left: 50%;
            top: 100%;
            width: 15px;
            height: 15px;
            background:
              radial-gradient(circle at 70% 35%,
                white, #66d63e 30%, #40a31d 50%);
        }

        .pendulum:after {
            content: "";
            position: absolute;
            left: 50%;
            transform: translate(-50%);
            top: 115%;
            border-radius: 50%;
            filter: blur(5px);
            width: 25px;
            height: 3px;
            background: rgba(0, 0, 0, 0.3);
        }
    </style>
</head>

<body>
    <div class="pendulum-base">
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
        <div class="pendulum"></div>
    </div>
</body>

</html>