it's time for us to talk about the twin ideas of mass and weight as long as we stay firmly here on the surface of the earth the force of gravity is equal to your mass and so mass and weight are equal so this device is measuring weight here we're measuring mass we're comparing that quantity of matter to this quantity of matter we're measuring mass but here on the surface they get the same answer now let's take these devices to the moon if we go to the moon let's see the gravitational constant is still the same and your mass is still the same your mass doesn't change because you fly to the moon does it but is the second mass the mass of the earth still the mass of the earth if you're standing on the moon that's now the mass of the moon that number has changed and d is no longer the radius of the earth it's the radius of the moon that number has changed as well so you are going to have to recalculate the relationship between the force of gravity pulling on you and your mass because those numbers are now different from what they were on the earth and so your mass is the same as it was before you got onto the rocket and went to the moon but your weight is entirely different and if you've seen video of astronauts working on the surface of the moon you'll know that their weight is indeed entirely different they don't walk normally in fact they found that the easiest way of progressing was in bunnyhops both feet together because unlike here on earth where a bunny hop is very awkward and very slow one bunny hop on the moon they could hop several feet and that seemed to be the easiest way of progressing one foot in front of the other one or two of the astronauts experimented with that and found you could run that way but it's lower speeds you wanted both your both your feet together your weight on the moon after recalculating is about 1 6 of your weight on earth your mass unchanged so on the moon any device that compares masses will get the exact same answer that it did on earth any device using a spring whether it's compressing the spring to get a weight or a device where you hang something and stretch the spring to get a weight those will record a very different answer on the moon from those on earth because you're using the force to make the measurement this one might be a little confusing because you need to have gravity to make the measurement but there's a big difference in this case you're measuring the amount of gravity here all you need is the gravity pull on both sides so that you can strike a balance the amount of gravity is not important just as long as it's the same all the way across the instrument okay mass and weight very different we abuse these terms seriously on earth take a weight loss program is the purpose of a weight loss program to reduce the pull of gravity on you absolutely not the purpose of a so-called weight loss program is to reduce the amount of matter within your body it's a mass loss program isn't it hey if you want to lose weight move to a smaller planet it's easy if you want to lose mass that's harder it involves dieting and exercise and what hey if you want to lose some weight move to denver why denver denver is the mile high city the radius of the earth in denver is one mile greater than it is here in southern california and so d has increased d squared has increased a tad more and so your weight has gone down just by moving to denver because you put on that weight again the moment you fly back to l.a because the gravity has increased again all right so mass and weight different things mass the amount of matter within you weight the pull of gravity on that mass