Subject: effect of positions of weights on a bar

When I lift weights I put the heaviest weights on the inside of 
the bar like normal.  If I switch them around and put the 
lightest weights on the inside of the bar and the heaviest 
towards the outside it seems to be heavier to lift.  Also, if the 
weights are spread out more on a longer bar (if that bar weighs 
the same as the shorter bar), the overall effect seems to be that 
the weights are heavier.  Can you explain this (please include 
formulas) or is it my imagination?

Re: effect of positions of weights on a bar