Balderdash. It can't possibly be exponential. Exponential would mean that for every meter of length you added, the weight would be multiplied by a constant fa

Balderdash. It can't possibly be exponential. Exponential would mean that for every meter of length you added, the weight would be multiplied by a constant factor. I would expect it to be roughly cubic, as you suggest. I don't know if it's exactly cubic. Even if it's a little worse than cubic, there is a vast difference between any power law and an exponential. I have, of course, observed the tendency, which seems to have increased in recent years, for science journalists to characterize any superlinear progression as exponential, but as an MIT alum I am quite unhappy to see this repeated in Technology Review.