I have a ball as a sphere in my game and I'm viewing it from top down view. The ball is a rigid body.

When I click somewhere on the screen, I want the ball to be moved towards that direction using physics forces.

The ball needs to move only on the X and Y axes, the Z axis can be ignored.

Here is what I tried, but gives me some weird results. The script is attached to the ball:

// Use this for initialization
    void Start () {
        rb = gameObject.GetComponent<Rigidbody> ();

    void Update () {

        Vector3 v3 = gameObject.transform.position;
        Vector3 v3Mouse = Input.mousePosition;

        Vector2 pointA = new Vector2(v3.x, v3.y);
        Vector2 pointB = new Vector2(v3Mouse.x, v3Mouse.y);

        float Angle = Vector2.Angle(pointA, pointB);
        float angleRad = Angle * (Mathf.PI / 180);

        Debug.Log ("Angle: " + Angle);
        float dx = Mathf.Cos (angleRad) * 10;
        float dy = Mathf.Sin (angleRad) * 10;

        if (Input.GetMouseButtonDown (0)) {

            rb.velocity = new Vector3(dx, dy, 0);



What should I do here? When I click on the top of the screen, the ball should move up toward the mouse, and in all the other directions.

Any ideas?


Vector mathematics! Assuming you're using Unity, you could use the inbuilt functions of Vector2:

transform.position = Vector3.MoveTowards(transform.position, target, speed);

Otherwise, here's how it's done - first, calculate the direction from point A to point B:

public static float Length(float x, float y) {
    return Math.Sqrt(x * x + y * y);

public static Vector2 Direction(Vector2 position) {
    return new Vector2(position.X / Length(position.X, position.Y), position.Y / Length(position.X, position.Y);

Direction will return a Vector2 representing the direction towards the position as values from -1 and 1 on both the X and Y axis. This is a Normalized Vector. In the case of finding the direction towards a target, you need to pass it the target's position subtracted by the current position:

Vector2 direction = Vector2.Direction(target - position);

You can use this to move your ball to the desired position:

position += direction * speed;

And you can also use it to make the object rotate towards (face) the desired position, although with it being a ball, it doesn't seem necessary, but regardless:

float angleInRadians = Math.Atan2(direction.Y, direction.X);
float angleInDegrees = angleInRadians * 180 / Math.PI;
  • \$\begingroup\$ Thanks for the comment, but I need to use it on a rigitbody, I tried like: rb.velocity = new Vector3(direction.x * 5, direction.y * 5, 0); but it does not work....what to do? \$\endgroup\$
    – mirzahat
    Jul 19 '15 at 16:27

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