ArrayList particles;

PVector dissipativeForce = new PVector();

void setup() {
 size(400, 400); 
 stroke(0);
 strokeWeight(3);
 fill(150);
 smooth();
 particles = new ArrayList();
}

void draw() {
  background(255);
  //only create when mouse moves
  if (abs(mouseX-pmouseX) > 0.0001) {
    particles.add(new Particle()); 
  } 
  for (int i = particles.size()-1; i >= 0; i--) {
    Particle p = (Particle)particles.get(i);
    // experiment w/ different friction coefficients
    applyDissipativeForce(p, 0.08); 
    if(!p.exist()) {
      particles.remove(i);  
    }
  }  
}

void applyDissipativeForce(Particle p, float friction) {
  PVector f = PVector.mult(p.velocity, -friction);
  p.applyForce(f);
}


public class Particle {
  PVector location;
  PVector velocity;
  PVector acceleration;
  float mass;
  
  public Particle() {
      location = new PVector(mouseX, mouseY);
      //get velocity from direction and speed of mouse movement
      velocity = new PVector(mouseX-pmouseX, mouseY-pmouseY);   
      acceleration = new PVector(0, 0, 0);
      mass = 1;
  }
 
  public boolean exist() {
     //when it comes to a rest, get rid of it
     if (abs(velocity.x) < 0.001 && abs(velocity.y) < 0.001) {
       return false;
     } 
     velocity.add(acceleration);
     location.add(velocity);
     ellipse(location.x, location.y, 10, 10); 
     acceleration.mult(0);
     return true;
  }
  
  void applyForce(PVector force) {
      acceleration.add(PVector.div(force, mass));
  }
    
}