Canvas velocity acceleration

HTML

<canvas id="canvas" width="500" height="400" style="border:1px solid #000000;"></canvas>

JavaScript

// get the theory behind:
// http://nepraunig.com/wp/?p=178

// grab the canvas and context
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');

// inital coordinates of the black square
var x = 0;
var y = 200;

// speed of the movement in x- and y-direction
// actual no movement in y-direction
var vX = 1;
var vY = 0;

// acceleration of the movement
// actual no acceleration in y-direction
var aX = 0.1;
var aY = 0.9;

// width and height of the square
var width = 10;
var height = 10;

function animate() {
    // clear
    // comment this clear function to see the plot of the sine movement
    ctx.clearRect(0, 0, canvas.width, canvas.height);    
    
    // apply acceleration
    vX += aX;
    vY += aY;
    
    // apply velocity
    x += vX;
    y += vY;
    
    // if the block leaves the canvas on the right side
    // bring it back to the left side
    if(x>500) {
        x = 0;
        // reset the acceleration and the velocity
        vX = 1;
        vY = 0;
        aX = 0.1;
        aY = 0;
    }
    
    ctx.fillRect(x, y, width, height);
    
    setTimeout(animate, 33);
}
// call the animate function manually for the first time
animate();