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Leonardo
da Vinci was one of the first people to formalize observations on friction.
In his Codex Atlanticus and Codex Arundel he shows sketches of friction experiments.
In (a), horizontal and inclined planes are used to investigate the
sliding of a block under the action of gravitational, tractive and friction forces, and (b) illustrates an experiment that showed that the friction force
between the plane and the block is independent of their nominal contact area.
From these experiments Leonardo concluded that: i) the friction
was doubled if the weight of the object was doubled, and ii) the friction force
due to a given weight was independent of the contact area between the body
and the plane. He also introduced the concept of a "coefficient of friction"
as the ratio between the friction force and the normal load, viz.
m = (F/W).
The measurements suggested
that the coefficient of friction was constant for all bodies and equal
to 0.25, i.e. the friction force was one quarter of the weight of the body.
Although this is not universally correct, it is a reasonable value for many
of the materials used in the tests.
Unfortunately, da Vinci's work
on friction was largely undiscovered until the 1960's and the "Laws"
based on these observations are associated with Amontons and Coulomb.
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