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Question by beakr · Dec 03, 2013 at 11:14 PM · physicsrigidbodygravitycircle

Add Gravitational Attraction to RigidBody2D?

I want to make a platformer with the style of Angry Birds Space's great outerspace physics. To do this, I need to make a planet sprite have a gravitational force. To do this, I added a CircleCollider2D, which has a RigidBody2D I can alter. How can I add gravitational attraction to this object's RigidBody2D? C# code examples would be appeciated.

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avatar image xiy · Dec 03, 2013 at 11:45 PM 0
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By gravitational attraction do you mean a genuine gravity simulation or a simple gravity simulation?

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Answer by hav_ngs_ru · Dec 04, 2013 at 09:10 AM

for simple simulation try this

 public GameObject planet; // assign your planet GO in unity editor here
 public float gravityFactor = 1f; // then tune this value  in editor too
 
 void FixedUpdate(){
 rigidbody.AddForce((planet.transform.position - transform.position).normalized * rigidbody.mass * gravityFactor / (planet.transform.position - transform.position).sqrMagnitude);
 }

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Answer by Downstream · Dec 04, 2013 at 09:10 AM

You need to calculate the direction components, normalize them and then add a force to that vector, whose strength is defined by the inverse-square law:

 var intensity = 5.5f;
 components = transform.position.planet - transform.position.ship;
 comp_normalized = components / components.magnitude;
 force = comp_normalized * (intensity * (1 / Vector2.Distance(from, end)))
 rigidbody2D.addForce(force);

Play around with intensity, to suit your needs. (I don't know C#, sorry.)

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Answer by MrVerdoux · Dec 04, 2013 at 08:07 AM

Something like a central force? Something like this maybe, but I´m not sure what you mean:

 Transform worldCenter;
 private readonly static float gravity = 0.1f; 

 void Update(){
     AddGravitationalForce();
 }
 
 void AddGravitationalForce(){
     Vector3 force = (transform.position - worldCenter.position)
     force = force.normalized/force.sqrMagnitude;
     force *= gravity*Time.deltaTime;
     rigidbody2D.AddForce(new Vector2(force.x, force.y));
 }
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