the physicsforums conversation doesn't seem to go anywhere , and neither has this one. It seems like the poster is taking issue with the assumption that lead does not have the same density as the planet. i think you are having problems with definitions and are not willing to understand the words, and are hoping that there are others out there who can better explain your paradox. but you are the one who is in charge of your thoughts. gravity is just a label. it exists in the same way your hand exists. density is a function of mass. saying it can have an affect on gravity while mass can't is a fundamental misunderstanding of what density means. for practical purposes density = mass. You can't have one without the other. it is not semantics. these are important concepts that one needs to understand first before being able to discuss them. and you say the cavendish experiment "doesn't work." I guess I'm confused how watching videos of it. What exactly is not working about the experiment.