I am looking at this website. I understand that Fn = mg. It has a question on the page saying: What is the normal force acting on the same person on the Moon? Well, I know that the moon''s gravity is 1/6 that of the Earth. If the person weighs 115 N(newtons), shouldn''t it be: Fn = 115 * (1/6 g)? It came up on my calculator that 1/6 9.8(Earth''s Gravity) = 1.6333333... I put in 115 * 1.63, but it just gave me 187.45. In the answer box, it says ''Correct Answer: 114.3''. I know that I''m calculating it wrong, but how?

One thing to mention is that weight isn''t the same as the mass (notice, the unit is N, not kg). Actually it is allready a force. But how to get 114.3N from 115N? I don''t know.

Well first of all Normal force does not always equal mg. It all depends on if any other forces are acting on the object and what angle that force is being applied at.

Second to solve this problem you have must first find the person''s mass.

So its 115 N = m(9.8) so m = 115/9.8 = 11.735 kg.
Then you can find the normal force on the moon.

Fn = 11.735(1.63333333) which = 19.17 N.

Also doing 115/6 will also work since we know that the moon''s gravity is 1/6 of that of the earth''s.

There is no way 114.3 can be the normal force on the moon if the normal force on earth is 115 unless some other force is acting upon it.

Is that 115 N the person''s weight on the moon or on Earth? If it''s the person''s weight on the moon then the normal should be the same; that would verify the 114.3 answer, although I wouldn''t be able to explain why it''s 0.7 off.

Otherwise, you convert the newton weight to mass, move that mass to the moon, and recalculate the newton weight with the moon''s gravity:

115 / 9.8 = 11.73 kg

If the moon''s gravity is 1/6 Earth''s (I''ll take your word for it):

9.8 * 1/6 = 1.63

That mass moved to the moon:

11.73 * 1.63 = 19¹/₆

Or, you could simply multiply the original weight by 1/6. Either way, it''s a lot smaller than 114.3

I have any idea. Don''t multiply by 9.8 again. Why would you in the first place if that is already factored in. This is why teachers have you show your work.

Well, your "idea" doesn''t help any. And I said that all you would have to do is multiply by 1/6, but sometimes it''s easier for someone to understand something if they see every discrete step, and then look for the shortcuts.