# Do I weigh 50 kg or 50 * 9.8 kg?

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## Main Question or Discussion Point

When I take my weight, it often shows around 50 kg. However, in my Astronomy class currently, it was mentioned that an average person's mass is roughly around 50 kg.

So, which one of them is correct? It doesn't make sense for my weight to be 50 kg because kg isn't exactly a unit of force, but then do I really weigh 490 N? (I'm so fat!)

Thanks!

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CWatters
Homework Helper
Gold Member
On earth your mass is 50kg and your weight (the force you exert on the ground) is 490 Newtons.

On the moon your mass would still be 50kg but your weight would be 81 Newtons because gravity is lower.

Most weighing scales (unsurprisingly) measure weight not mass but because they are intended for use on the earth only they are marked in Kg because that's what people are familiar with. They won't work correctly on the moon.

fresh_42
Mentor
(I'm so fat!)
Just say you weigh .5 kN.

CWatters
Homework Helper
Gold Member
http://www.learnwithmac.com/2015/03/27/what-do-scales-measure/

..how do you know that your scale is actually reading force [weight] and not mass? Well there is an easy way to confirm this. Stand on your scale close to a fixed object and then carefully push yourself down on the scale using the fixed object as a support. You will suddenly see the scale reading increasing, indicating that your mass has increased. However this is not the case since you haven’t suddenly put on mass.

CWatters
Homework Helper
Gold Member
I only weigh 21 Newtons*

*(on Ceres)

fresh_42
Mentor