This picture shows a couple of Mk-76 25lb (11kg) Inert Training Bombs on a McDonnell Douglas AV-8B Harrier II; it's clear that the physical characteristics of the dummy bomb are quite different to actual munitions.
One obvious advantage of the smaller, lighter bombs is that they're vastly cheaper to operate, both in terms of handling on the ground and the amount of fuel you'd be using in the air. However, the dummy bomb is 20 times less massive than the bomb its designed to simulate: its small size and weight surely mean their aerodynamic characteristics are very different to the bombs they're supposed to be simulating. (I know that speed of fall in a vacuum is not dependent on weight, but a falling object in air is affected by shape, weight, drag etc.)
My question is - since their purpose is presumably to help train the pilots, how can tiny dummy bombs usefully simulate real bombs?