This example is for Processing 3+. If you have a previous version, use the examples included with your software. If you see any errors or have suggestions, please let us know.

Chain.

One mass is attached to the mouse position and the other is attached the position of the other mass. The gravity in the environment pulls down on both.

```

Spring2D s1, s2;

float gravity = 9.0;
float mass = 2.0;

void setup() {
size(640, 360);
fill(255, 126);
// Inputs: x, y, mass, gravity
s1 = new Spring2D(0.0, width/2, mass, gravity);
s2 = new Spring2D(0.0, width/2, mass, gravity);
}

void draw() {
background(0);
s1.update(mouseX, mouseY);
s1.display(mouseX, mouseY);
s2.update(s1.x, s1.y);
s2.display(s1.x, s1.y);
}

class Spring2D {
float vx, vy; // The x- and y-axis velocities
float x, y; // The x- and y-coordinates
float gravity;
float mass;
float radius = 30;
float stiffness = 0.2;
float damping = 0.7;

Spring2D(float xpos, float ypos, float m, float g) {
x = xpos;
y = ypos;
mass = m;
gravity = g;
}

void update(float targetX, float targetY) {
float forceX = (targetX - x) * stiffness;
float ax = forceX / mass;
vx = damping * (vx + ax);
x += vx;
float forceY = (targetY - y) * stiffness;
forceY += gravity;
float ay = forceY / mass;
vy = damping * (vy + ay);
y += vy;
}

void display(float nx, float ny) {
noStroke();
ellipse(x, y, radius*2, radius*2);
stroke(255);
line(x, y, nx, ny);
}
}
```