SI, the units of mass, length, and time are the kilogram (kg), meter (m),
and second (s), respectively. The respective units in the English system are
the pound-mass (lbm), foot (ft), and second (s). The pound symbol lb is
actually the abbreviation of libra, which was the ancient Roman unit of
weight. The English retained this symbol even after the end of the Roman
occupation of Britain in 410. The mass and length units in the two systems
are related to each other ,In the English system, force is usually considered to be one of the primary.
dimensions and is assigned a nonderived unit. This is a source of confusion
and error that necessitates the use of a dimensional constant (gc) in
many formulas. To avoid this nuisance, we consider force to be a secondary
dimension whose unit is derived from Newton’s second law, that is,
In SI, the force unit is the newton (N), and it is defined as the force required
to accelerate a mass of 1 kg at a rate of 1 m/s2. In the English system, the
force unit is the pound-force (lbf) and is defined as the force required to
accelerate a mass of 32.174 lbm (1 slug) at a rate of 1 ft/s2 (Fig. 1–7). That
is,A force of 1 N is roughly equivalent to the weight of a small apple (m
102 g), whereas a force of 1 lbf is roughly equivalent to the weight of four
medium apples (mtotal 454 g), as shown in Fig. 1–8. Another force unit in
common use in many European countries is the kilogram-force (kgf), which
is the weight of 1 kg mass at sea level (1 kgf 9.807 N).
The term weight is often incorrectly used to express mass, particularly by
the “weight watchers.” Unlike mass, weight W is a force. It is the gravitational
force applied to a body, and its magnitude is .hermodynamics did not emerge as a science
until the construction of the first successful atmospheric steam engines in
England by Thomas Savery in 1697 and Thomas Newcomen in 1712. These
engines were very slow and inefficient, but they opened the way for the
development of a new science.
The first and second laws of thermodynamics emerged simultaneously in
the 1850s, primarily out of the works of William Rankine, Rudolph Clausius,
and Lord Kelvin (formerly William Thomson). The term thermodynamics
was first used in a publication by Lord Kelvin in 1849. The first
thermodynamic textbook was written in 1859 by William Rankine, a professor
at the University of Glasgow.
It is well-known that a substance consists of a large number of particles
called molecules. The properties of the substance naturally depend on the
behavior of these particles. For example, the pressure of a gas in a container
is the result of momentum transfer between the molecules and the walls of
the container. However, one does not need to know the behavior .