krappleby

HI all, OK, I am here to question some science that my son brought home the other night, He wasn't sure how to do it so i sat down with him and went through it, and he got all his answers Wrong.. but as far as i'm concerned they are not wrong, and from what i've read on the internet Science is wrong.. Let me explain The homework, was a list of planets, with their gravitational pulls, he had to mark down his weight (4 stone 6) and then in the first two columns put his mass, and weight on each planet. Now. he got it wrong because apparently according to Science, his mass is the same on all planets (this is also what his teacher said), But i;m afraid to say it is Not. Let me explain. To work out the mass of an object, you take its density and multiply it by its volume, this gives you the mass. now, to work out your density you take your weight and divide by your volume now since your weight is effected by gravitational pull, your mass on earth and mars is completely different. since your weight is different. so my question is, How can your mass be identical no matter what planet your on, when your mass is effected by your weight, and your weight is effected by the gravitational pull of the planet? please if i'm missing something here, then feel free to enlighten me, but as far as i'm concerned, the teacher and science is wrong.