Environmental Engineering Reference
In-Depth Information
As man developed tools, such as axles or levers, to make his work easier, a great
effort was made to find machines that could perform work without the need of
muscular effort. The human spirit has always been fascinated by the idea of build-
ing a “perpetuum mobile” or perpetual motion machine, which, once set in motion,
would never stop. All the efforts to build such machines failed. The reason for such
failures is the nature of Newton's law of gravitational force; energy performed in-
volving the force of gravity is always conserved, that is, remains constant and can-
not be created or destroyed. For example, if a body falls from a given height, a giv-
en and constant amount of work is performed. To lift the body to the same height
requires exactly the same amount of work as is performed when the object falls,
independent of the trajectory one follows in order to lift the object.
This is a most fundamental discovery because it means that energy cannot be
created or destroyed. The consequence is that it is impossible to construct a ma-
chine in the gravitational field that produces mechanical work, such as grinding
cereals, without the addition of a source of energy from outside the system.
Robert Fludd made one of the most interesting proposals for a “perpetuum mo-
bile” machine in 1630 (
Figure 1.1
)
. He designed a machine in which the force of
gravity would move a waterwheel connected to an endless bolt, which would, in
turn, move all the water back to the original reservoir; the turning of the water
wheel would drive a device to grind corn or other cereals.
Obviously this contraption didn't work.
