Lose Weight Instantly on a Low Gravity Diet

If you’ve seen videos of astronauts bouncing around on the moon, you know that they fall more slowly up there. Even though their suits are very heavy, they can still spring easily off the ground with each step, because you feel much lighter on the moon than you do here on earth.  You could take a scale with you to find just how much lighter, but you might be surprised to learn that the answer you’d get would depend on the type of scale!

If it were a bathroom scale, like most people have at home, it’d tell you that you weigh 16.6% of your current weight, because the moon is much less massive than the Earth. If you weigh 150 pounds here at home, you’d weigh about 25 pounds on the moon (and your high-jump would improve accordingly!) That’s because how much you weigh depends not only on YOUR mass (how much matter is in your body), but also the mass and size of the planet you’re on.

But if you used a beam-balance scale, like the ones you see at a doctor’s office, it would say your weight hasn’t changed from what it was on earth, even though you’d still feel much lighter.

So why the difference?

Even though a beam-balance scale looks complicated, it works essentially the same as a pan-scale like the one seen below:

When you step onto the scale, it’s like stepping on one of the pans, and when your doctor slides the metal weights along the beams, it’s like adding weights to the other pan. By adding weights until the two pans are at equal heights, we can tell how much a person weighs.

If you took the whole apparatus to the moon, the weights in the other pan would lose just as much weight as you, so it would take the same amount of mass to bring the pans level.

But most bathroom scales don’t work like this; instead, many use springs to measure your weight. When you jump on a bed, you’re compressing the springs inside the mattress, squishing them down. How much they compress depends on how much you weigh and something called the spring constant (which depends on what the spring is made of and how it’s manufactured). Similarly, a spring scale on the moon would tell you accurately how hard the moon is pulling you down, since the spring constant doesn’t change depending on where you are.