I understand everything else about them, just not why they're the wrong way up!!
This is more of a rationalisation than a true explanation, but anyway... We know that gravity is an attractive force, and presumably you also know that a system will tend to move towards the lowest energy state? Given this it follows that the potential will be lower as the distance between two particles decreases.
That's a very non-technical explanation, but hopefully it helps a little; if you want something more detailed, just follow M_E_X's link.
We know that gravity is an attractive force, and presumably you also know that a system will tend to move towards the lowest energy state? Given this it follows that the potential will be lower as the distance between two particles decreases.
That's a very non-technical explanation, but hopefully it helps a little; if you want something more detailed, just follow M_E_X's link.
That's right, exactly . We say bodies can fall in to a "potential well", and this makes sense with potential being negative. If potential was positive and a body was on the top of a "potential hill", it would just roll down and hence escape from the potential - this wouldn't make sense.