||Original scetches from Leonardos experiments on friction.
Leonardo da Vinci has the credit to be the first who made quantitative
studies on the problem of friction. Leonardo's experimental setup for
friction measurements was rather simple. He measured the angle a
of an inclined plane, where a body, put on the plane, started sliding
and the weight needed to make a block on a table moving. With his methods he was only able to measure static
friction and most probably he wasn't aware of the difference between
static and kinetic friction. Leonardo found the following two laws of
friction, in which we essentially recover friction laws 1 and 2.}
- The friction made by the same weight will be of equal
at the beginning of its movement although the contact may be
breadths and lengths.
- Friction produces double the amount of effort if the
weight be doubled.
Leonardo defined a friction coefficient as the ratio of the friction
divided by the mass of the slider. Experimentally, he found a universal
friction coefficient of 0.25 independent of the material. This universal
friction coefficient of 0.25 is called Bilfinger value. Many other
friction scientists after Leonardo believed in the existence of a
universal material independent friction coefficient. However, most of
them found another value but all in the range 0.1 - 0.6.