Friction of pivots versus dragging
Distributing a load over many pivots does not reduce the total friction
Leonardo asks what difference there is between the circular friction of turning pivots and the straight friction of objects simply dragged. A small cluster of wheels pivoted together is drawn to test the idea. He grants that such an arrangement distributes the weight over several pivots, but argues that gathering all those small reliefs together yields the same total resistance as before. He likens it to a pound divided into twelve ounces, which recombine into exactly the same pound.
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Circular versus straight friction
The opening question contrasts the circular friction of pivots with the straight friction of things that are dragged. It frames the whole inquiry into how resistance behaves in rolling versus sliding.
Distributing load over many pivots gains nothing
In a cluster of wheels pivoted together the weight is truly distributed among several pivots, yet summing all those reliefs restores the same difficulty as before. Leonardo compares it to a pound split into twelve ounces that, regathered, recompose exactly the same pound.