Why Heavy Bodies Fall: Water in a Bent Tube
Weight moves downward where it meets no resistance, not to reach the centre
Beside a diagram of a tube bent at an angle, Leonardo states that water running through a pipe of uniform bore fills all its straight and oblique sections and moves with equal speed. He then advances a physical thesis: heavy elements move not in order to reach the centre of the world, but because the medium around them cannot resist them, and once they meet resistance they cease to weigh or seek the centre. Water in air descends by the shortest path, dividing the air beneath its centre of gravity, and stops seeking the centre once it strikes the resisting water below.
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Water in a uniform bent pipe moves at equal speed throughout
Water running through a pipe of equal hollowness that fills all of its first flat part will fill all the other straight and oblique parts as well, and will move with equal velocity throughout. The accompanying diagram shows a tube bent at an angle.
Heavy bodies fall for lack of resistance, not to reach the centre
Leonardo argues that heavy elements move downward not in order to reach the centre of the world but because the medium in which they sit cannot resist them; once resistance is met, the body no longer weighs or seeks the centre. Water in air descends by the shortest way, dividing the air beneath its centre of gravity equally with all its parts and boring a very short hole through it until it meets resistance. On reaching the water below, it no longer divides the medium and so no longer seeks the centre; therefore weight moves downward simply where it finds no resistance.