Science Buddies: "Ask an Expert"

When determining the GPE, do I multiply the mass of the marble(which I weighed on gram scale) by 9.8 by height. Or is the 9.8 already included in it because I weighed it on a scale?

If your scale is displaying mass, it's already accounted for gravity and what's displayed is simply the mass. You need to use g in your calculation.

Howard

How do you know if the scale is just measuring mass? I purchased the digital scale suggested on this website. MS-600.

That's how scales work. A true mass scale would be balancing one mass against another to eliminate the miniscule differences in gravity based on altitude. Most scales though, use springs or the digital equivalent to give you a reading that assumes the standard definition of gravity. Your scale is really measuring weight, but that's okay. If you were on the moon doing this experiment you'd have an excellent point. But here on earth, that scale is just fine and it's giving you mass in grams as it should.

Howard

Great. Thank you so much for the clarification! I really appreciate your assistance.