<?php

$isGravity = false;

$g = 6.67408E-11;//    m3⋅kg–1⋅s–2
$coulomb = 8.9875517923E9;

//Parameters
if ($isGravity)
{
    $m1 = 1;
    $m2 = 5.972E24;
    $distance = 1000000000000;
} else {
    $m1 = 9.10938356E-31;
    $m2 = 1.6726219E-27;
    $distance = 1;
}

//Init variables
$initialDistance = $distance;
$distanceAdditional = 1.0581106794609E-10;
$jouleToEv = 6.242E18;

$v1 = 0;
$v2 = 0;
$time = 1000000000000000;
$totalTime = 0;
$i = 0;

$steps = 10000000000;
while ($distance > 0)
{
    if ($isGravity)
        $force = ($g * $m1*$m2)/($distance * $distance);
    else
        $force = ($coulomb *  1.60217646E-19 *  1.60217646E-19)/($distance * $distance);

    $a1 = $force / $m1;// + ($force2 / $m1);
    $a2 = $force / $m2;

    while ($initialDistance < (($a1 *  $time) * $time) * $steps)
    {
        $time /= 2;
    }

    while ($initialDistance > (($a1 *  $time) * $time) * $steps)
    {
        $time *= 2;
    }

    while ($a1 *  $time > 100)
    {
        $time /= 2;
    }

    $v1 += $a1 *  $time;
    $v2 += $a2 *  $time;

    $energy1 = $m1 * $v1*$v1 / 2;
    $energy2 = $m2 * $v2*$v2 / 2;

    /*
    echo "multi: ".($a1 *  $time)."\n";
    echo "a1: ".($a1)."\n";
    echo "v1: ".($v1)."\n";
    echo "time: ".($time)."\n";
    echo "force: $force\n";
    echo "distance: $distance\n";
    echo "time: $time\n";
    echo "----\n";
    */

    if ($isGravity)
    {
        if ($distance < 6371000)
            break;
    } else {
        if ($energy1 * $jouleToEv > 13.6*2)
            break;
    }

    $distance -= $v1 * $time;
    $distance -= $v2 * $time;

    echo "distance after : $distance\n";

    $totalTime+= $time;
}

echo "------\n";
echo "V1: $v1\n";
echo "V2: $v2\n";
echo "A1: $a1\n";
echo "A2: $a2\n";
echo "M1: ".($m1 * $v1)."\n";
echo "M2: ".($m2 * $v2)."\n";
echo "Total Time: $totalTime\n";
echo "Distance: $distance\n";
echo "Energy1: $energy1, eV: ".($energy1 * $jouleToEv)."\n";
echo "Energy2: $energy2, eV: ".($energy1 * $jouleToEv)."\n";
?>