const numParticles = 100;

let magnetActive = false;

let magnetStrength = 1000;

​

function setup() {

  createCanvas(800, 600);

  // Initialize particles in a pool at the bottom

  for (let i = 0; i < numParticles; i++) {

    particles.push(new Particle(

      random(width),

      random(height/2, height),

      random(2, 4)

    ));

  }

}

​

function draw() {

  background(240);

  // Draw magnet indicator

  drawMagnet();

  // Update and display particles

  for (let particle of particles) {

    // Apply gravity

    let gravity = createVector(0, 0.2);

    particle.applyForce(gravity);

    // Apply magnetic force if active

    if (magnetActive) {

      let magnetPos = createVector(mouseX, mouseY);

      let magneticForce = particle.calculateMagneticForce(magnetPos);

      particle.applyForce(magneticForce);

    }

    particle.update();

    particle.checkEdges();

    particle.display();

  }

}

​

function mousePressed() {

  magnetActive = true;

}

​

function mouseReleased() {

  magnetActive = false;

}

​

function drawMagnet() {

  push();

  translate(mouseX, mouseY);

  if (magnetActive) {

    fill(255, 0, 0);

    // Draw magnetic field lines

    for (let angle = 0; angle < TWO_PI; angle += PI/8) {

      let x = cos(angle) * 30;

      let y = sin(angle) * 30;

      line(0, 0, x, y);

    }

  } else {

    noFill();

  }

  stroke(0);

  strokeWeight(2);

  circle(0, 0, 20);

  pop();

}

​

class Particle {

  constructor(x, y, radius) {

    this.pos = createVector(x, y);

    this.vel = createVector(0, 0);

    this.acc = createVector(0, 0);

    this.radius = radius;

    this.mass = radius;

    this.drag = 0.98;

  }

  calculateMagneticForce(magnetPos) {

    // Calculate direction and distance to magnet

    let force = p5.Vector.sub(magnetPos, this.pos);

    let distance = force.mag();

    // Set minimum distance to avoid extreme forces

    distance = constrain(distance, 20, 1000);

    // Calculate force magnitude using inverse square law

    let strength = (magnetStrength * this.mass) / (distance * distance);

    force.setMag(strength);

    return force;

  }

  applyForce(force) {

    let f = p5.Vector.div(force, this.mass);

    this.acc.add(f);

  }

  update() {

    this.vel.add(this.acc);

    this.vel.mult(this.drag); // Apply drag

    this.pos.add(this.vel);

    this.acc.mult(0);

  }

  checkEdges() {

    // Bounce off edges with energy loss

    if (this.pos.y > height - this.radius) {

      this.pos.y = height - this.radius;

      this.vel.y *= -0.6;

    }

    if (this.pos.y < this.radius) {

      this.pos.y = this.radius;

      this.vel.y *= -0.6;

    }

    if (this.pos.x < this.radius) {

      this.pos.x = this.radius;

      this.vel.x *= -0.6;

    }

    if (this.pos.x > width - this.radius) {

      this.pos.x = width - this.radius;

      this.vel.x *= -0.6;

    }

  }

  display() {

    // Calculate color based on velocity

    let speed = this.vel.mag();

    let hue = map(speed, 0, 10, 200, 360);

    colorMode(HSB);

    fill(hue, 80, 90);

    colorMode(RGB);

    noStroke();

    circle(this.pos.x, this.pos.y, this.radius * 2);

  }

}