My Sketch

let xPos, yPos, xVel, yVel, xAcc, yAcc

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function setup() {

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  createCanvas(500, 500);

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  xPos = yPos = width / 2

  xVel = 1

  yVel = 1

  xAcc = 0

  yAcc = 0

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}

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function draw() {

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  fill(34, 155, 215, 50); // r,g,b,a

  rect(0, 0, width, height)

  update()

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}

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function update(){

  move()

  checkBoundary()

  display()

} 

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function move() {

  xAcc += random(-0.001, 0.001)

  yAcc += random(-0.001, 0.001)

  xVel += xAcc

  yVel += yAcc

  xPos += xVel

  yPos += yVel

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}

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function checkBoundry() {

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  if ((xPos > width) || (xPos < 0)) {

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    // xPos = 0 

    xVel *= -1

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  }

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  if ((yPos > height) || (yPos < 0)) {

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    // yPos = 0 

    yVel *= -1

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  }

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}

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function display() {

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  let r = sin(millis() / 100) * 100

  fill(255,0,255)

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  circle(xPos, yPos, r); // x,y,r

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}