- #1
- 718
- 163
We say that, for gravity, F=mg, where g≈-9.8 m/s2. Then, we have U=mgh. But, it seems like that equation would only work if g were positive 9.8 m/s2. That is, because ##F=-\frac{dU}{dr}##, and ##\frac{dU}{dr}## is essentially ##\frac{dU}{dh}##, we should get F=-mg. So, for the two equations to work, it seems like the g in the first equation should have the opposite sign as the g from the second equation. But that seems like a really weird convention to have. So, if the convention is that g is positive then we should have F=-mg, and if g is negative we should have U=-mgh, right?