Page 47 - Physical chemistry understanding our chemical world

14 INTRODUCTION TO PHYSICAL CHEMISTRY

Some people might argue that none of the discussion above actu-
The word ‘philosoph-
ally answers the philosophical question, ‘What is temperature?’
ical’ comes from the We will never come to a completely satisfactory answer; but we
Greek words philos
can suppose a body has a higher temperature if it contains more
meaning ‘love’ and
sophia meaning ‘wis- energy, and that it has a lower temperature if it has less energy.
More importantly, a body will show a rise in temperature if its
dom’. Philosophy is
therefore the love of energy content rises, and it will show a lower temperature if its
wisdom. This same energy content drops. This is why we sit in front of a fire: we want
usage of ‘wisdom’ is to absorb energy, which we experience as a higher temperature.
seen with the initials
PhD, which means a
‘philosophy doctorate’.

How long is a piece of string?

The SI unit of length
This definition of ‘more
energy means hotter’
needs to be handled A common problem in Anglo Saxon England, as well as much
with care: consider of contemporary Europe, was the way cloth merchants could so
two identical weights easily cheat the common people. At a market, it was all too easy
at the same tempera- to ask for a yard of cloth, to see it measured against the merchant’s
ture. The higher weight yardstick, and pay for the cloth only to get home to learn just how
has a greater potential short the merchant’s stick was. Paying for 10 yards and coming
energy.
home with only 9 yards was common, it seems; and the problem
was not restricted to just cloth, but also to leather and timber.
According to legend, the far-sighted English King Edgar (AD 959–975) solved the
problem of how to stop such cheating by standardizing the length. He took 100 foot
soldiers and measured the length of the right foot of each, one after the other, as
they stood in line along the floor of his threshing hall. This overall length was then
subdivided into 100 equal parts to yield the standard length, the foot. The foot is still
commonly employed as a unit of length in Britain to this day. Three of these feet
made up 1 yard. The king was said to keep in his treasury a rod of gold measuring
exactly 1 yard in length. This is one theory of how the phrase ‘yardstick’ originated.
Any merchant accused of cheating was required to bring his yardstick and to compare
its length against that of the king. Therefore, a merchant whose stick was shorter was
a cheat and paid the consequences. A merchant whose stick was longer was an idiot.
While feet and yards are still used in Britain and other countries,
the usual length is now the metre. At the time of the French Rev-
SI units are self- olution in the 18th century and soon after, the French Academy
consistent, with all
of Sciences sought to systemize the measurement of all scientific
units being defined in
terms a basis of seven quantities. This work led eventually to the concept of the Syst`eme
Internationale, or SI for short. Within this system, all units and
fundamental units. The
SI unit of length l is the definitions are self-consistent. The SI unit of length is the metre.
metre (m). The original metre rule was kept in the International Bureau
of Weights and Measures in S` evres, near Paris, and was a rod of