No option for Adding a force to a RigidBody2D without using Mass

Unity Engine
,
1

Im in the process of creating a 2D Physics-based space exploration game. I created a script which takes Objects from a list and applies Gravity to them based on Newton’s Formula, here is the script:

public class GravityConfig : MonoBehaviour
{
    public List<GameObject> GravList;
    private Rigidbody2D rb2;
    public float GravitationalConstant;
    public Vector3 ForceApplied;

    private float maxGravityDist = 0.01f;

    private Rigidbody2D rb;

    private void Start()
    {
        rb = GetComponent<Rigidbody2D>();
    }

    public void Gravity()
    {
        foreach (GameObject x in GravList)
        {
            rb2 = x.GetComponent<Rigidbody2D>();
            maxGravityDist = rb2.mass * 10;
            float dist = Vector2.Distance(x.transform.position, transform.position);
            Vector2 v = x.transform.position - transform.position;
            ForceApplied = v.normalized * GravitationalConstant * (1.0f - dist / maxGravityDist) * rb2.mass * Time.deltaTime;
            rb.AddForce(ForceApplied);
        }
    }
    private void FixedUpdate()
    {
        Gravity();
    }
}

As you may know, The speed at which an object falls actually has nothing to do with its mass but rather the gravitational field strength of the body it is falling towards. Unfortuantely, RigidBody2D.AddForce() uses the mass of the RigidBody to calculate it’s velocity. Using Rigidbody rather than Rigidbody2D however, there is an option to use ForceMode.Acceleration which applies a force to said rigidbody without the use of its mass. This is great because in my game, I want all objects to fall at the same speed regardless of its mass. Unfortunately, there is no such option for RigidBody2D and i cant find a workaround that doesn’t involve me rewriting the whole game. I thought i would come to the forums to request help from more seasoned game developers like you guys.

thanks in advance,
Ethan

2

Simply:

rb.velocity += ForceApplied;

… where in your case “ForceApplied” is the acceleration already time-integrated (scaled by the elapsed time).

Also, don’t use transform.position (or rotation) as the source of truth for the current pose when using physics. The source of truth and the thing that drives the Transform is obviously the Rigidbody2D and its position/rotation properties. If you use interpolation then the body will already be at the position you’re interpolating to.

3

I just get error: CS0034 Operator ‘+=’ is ambiguous on operands of type ‘Vector2’ and ‘Vector3’

4

It’s 2D physics so Rigidbody2D.velocity is a Vector2 not a Vector3 so change what you’re adding to a Vector2 or cast it to one.