Newtonian Gravity

Questions & Answers
1

I am attempting to make a realistic gravity simulation that can use the mass of an object to then calculate how much gravity it has using Newton’s law of universal gravity. Here is what I have so far:

function gravity(float m1, m2, r)
{
	f = 6.674 e -11 * m1 * m2 / (r * r);	
	
	return f;
}

Of course this is only a start, and I have no idea what to do from here. Any help is welcome!

2

Hello !
I had the same issue, and even if the topic is old, it could help someone…
So here’s a code. It’s pretty simple, but it works.

void ApplyGravity(Rigidbody A, Rigidbody B)
	{
        //This is how to get the distance vector between two objects.
		Vector3 dist = B.transform.position - A.transform.position; 
		float r = dist.magnitude;
   		dist /= r;

        //This is the Newton's equation
        //G = 6.67 * 10^-11 N.m².kg^-2
		float force = ((float)G * A.mass * B.mass) / (r * r);

        //Then, just apply the forces
		A.AddForce (dist * force);
		B.AddForce (-dist * force);
	}

Every “planet” or whatever must have the tag “Object”

void FixedUpdate () 
   {
        //Get every object 
		Objects = GameObject.FindGameObjectsWithTag ("Object");

        //the gravity between each couple of object is calculated
		foreach (GameObject ObjectA in Objects) 
		{
			foreach (GameObject ObjectB in Objects)
			{
                //Objects must not self interact 
				if(ObjectA == ObjectB)
					continue;

				ApplyGravity(ObjectA.rigidbody, ObjectB.rigidbody);
			}

		}
	}

I’m sorry, i’m not into Javascript, this is C#
Hope this will help ! Have a nice day.

3

Cool - for those of you who need the full class listing - here it is (in a class called GameManager)

-(this also gives a orbit between the two objects)

using UnityEngine;
using System.Collections;

public class GameManager : MonoBehaviour {

// Use this for initialization
void Start () {
	GameObject[] Objects = GameObject.FindGameObjectsWithTag ("Planet");
	
	//the gravity between each couple of object is calculated
	foreach (GameObject ObjectA in Objects) 
	{
		ObjectA.rigidbody.AddForce(new Vector3(100,0,0));
	}
}

void ApplyGravity(Rigidbody A, Rigidbody B)
{
	//This is how to get the distance vector between two objects.
	Vector3 dist = B.transform.position - A.transform.position; 
	float r = dist.magnitude;
	dist /= r;
	
	//This is the Newton's equation
	//G = 6.67 * 10^-11 N.m².kg^-2
	double G =  6.674f * (10 ^ 11);
	float force = ((float)G * A.mass * B.mass) / (r * r);
	
	//Then, just apply the forces
	A.AddForce (dist * force);
	B.AddForce (-dist * force);
}

void FixedUpdate () 
{
	//Get every object 
	GameObject[] Objects = GameObject.FindGameObjectsWithTag ("Planet");
	
	//the gravity between each couple of object is calculated
	foreach (GameObject ObjectA in Objects) 
	{
		foreach (GameObject ObjectB in Objects)
		{
			//Objects must not self interact 
			if(ObjectA == ObjectB)
				continue;
			
			ApplyGravity(ObjectA.rigidbody, ObjectB.rigidbody);
		}
		
	}
}

}