Of revolving motion: the spinning top
A top drawn upright, oblique, and horizontal as impetus and uneven weight contend for its axis.
This page is devoted to 'revolving motion,' studied through a spinning top (trottola, or humming-top) drawn in three states: upright, tilted oblique, and lying horizontal. Leonardo argues that while the impetus of the spin dominates, it suppresses the tendency of the top's uneven weight to make it lean and fall about the centre of rotation; when the weight's inequality overcomes the impetus the top lies down and spins out on that centre, and when the two powers are equal the top wobbles obliquely as they contend in a great circuit. The three figures are labelled first (upright), second (oblique), and third (horizontal).
On this page
The top while its impetus dominates
While the speed of its revolution makes the impetus dominate, the top (or humming-top) suppresses the power that the inequality of its weight has about the centre of rotation. The body will never lean over as its weight-inequality 'desires' until the power of the impetus that moves it becomes less than the power of that inequality. This figure is labelled 'first.'
When the weight's inequality wins
When the power of the weight-inequality overcomes the power of the impetus, that inequality becomes the centre of the revolving motion, and the body, laid down, finishes on that centre the remainder of its impetus. This figure is labelled 'third.'
When the two powers are equal
When the power of the weight-inequality becomes equal to the power of the impetus, the top bends obliquely and by a composite motion the two powers do battle, sweeping one another round in a great circuit until a centre settles into the 'second kind' of revolution, where the impetus ends its power. This figure is labelled 'second.'