I am applying the exact same force to all of these “balls”, yet there are variants in how fast they move:
Is this just a limitation of the physics engine? hopefully I am just missing something 
I got it!
It depends on earth Rotation!
just kidding, sorry
Are they Dynamic Object. If they are you wont get the same result on each ball. You have to use Kinematic Objects but you have to do some extra coding since your fully in control of its physic.
on “contact_point_response” check its normal to see what direction the collision occurred and update the x and y velocity separately. For example if the normal is pointing left that means the collision object the ball collided with was on the right that means you would set the x velocity to a negative speed etc etc