at home we noticed that a 1kg bag of flour feels heavier than a 1kg bag of coffee beans - unless you carry both on a plate, then they feel equally heavy.

science would be quick to call this a sensory illusion, but that is only if you expect weight perception to work like a mercantile scale.

i do think that what's going on here is that the mind also factors in how much it would hurt to throw this at someone's head, or how easy it would break if it fell.