Box2D Forums

Hi all,

I'm new to box2d, and i'm making games for android. There is something i want to ask,
I want to create an object which will pull other object, something like gravity / magnetic field,
while there is world gravity also so they will affecting each other.

I calculate how much force applied to other object like this:



I can't find what's wrong with this code, but no matter how much force I applied, the object doesn't seems to be pulled by the source.
Even if i change the force magnitude to 10000 it won't pull the object, unless i set the world gravity to zero. strange...

So I think maybe i use the applyForce not correctly, can any of you give me suggestion / solution?

Also, i want to know the difference between getWorldCenter and getPosition.

Thanks in advance.

I have test this further, and it seems that the gravity is somehow overpower the force.

but still it's strange i think. Box2d use meter and second right? so when i set the gravity as (0, -3),
it's the gravity acceleration of 3 m/s2 to negative y axis, am I right?

so if I apply the force to y positive, with magnitude body.getMass()*10, it gives acceleration of 10m/s2 upward,
it should be greater than the gravity? but it's not... strange...

did I miss something here? please, any help would be much appreciated.

it turns out that this problem is because improper use of force.mul()
it returns the multiplied force, but the force itself is not multiplied.

so the code should be like this

Yeah, mutable methods usually have the postfix "Local", so you would want to use "mulLocal()"