
Euler on the 10 franc banknote (Serie 1975  1995) 
The scientist Leonhard Euler, who was born in Basel and later moved to
St.~Petersburg is famous for his work in the field of mathematics. Less
is known about his important contributions in the field of friction
physics. He studied theoretically the mechanism of the sliding motion of
a block on an inclined plane. He adopted the model of rigid interlocking
asperities as the cause of frictional resistance. (Euler considered Leonardo's experiments
of the sliding block on the inclined plane.}
He assumed that the friction
force results from gravitational forces, trying to minimize the
potential energy of the block. He found the relation between inclination angle
a and friction coefficient
m. We find this relation also by equating the friciton force with the accelerating force:
Assuming a velocityindependent friction
coefficient, he found, that for the critical angle a the
acceleration of the block should be exceedingly small, since gravity is
nearly compensated by kinetic friction. This result was against the
experimental facts, where sliding started relatively fast. He concluded,
that one has to distinguish between static and kinetic friction and that
static friction is always larger than kinetic friction. With these
assumptions he was able to describe the motion of a block on an inclined
plane. Euler was the first who distinguished between static and kinetic
friction.
