6.8 Physical Laws and Observations in Engineering 149
We can use words to explain our observations or use another language, such as mathematics, to
express our findings. Sir Isaac Newton (1642 –1727) formulated that observation into a useful
mathematical expression that we know as the universal law of gravitational attraction.
An important point to remember is that the physical laws are based on observations. More-
over, we use mathematics and basic physical quantities to express our observations in the form
of a law. Even so, to this day we may not fully understand why nature works the way it does.
We just know it works. There are physicists who spend their lives trying to understand on a
more fundamental basis why nature behaves the way it does. Some engineers may focus on
investigating the fundamentals, but most engineers use fundamental laws to design things.
As another example, when you place some hot object in contact with a cold object, the hot
object cools down while the cold object warms up until they both reach an equilibrium tem-
perature somewhere between the two initial temperatures. From your everyday experience, you
know that the cold object does not get colder while the hot object gets hotter! Why is that? Well,
it is just the way things work in nature! The second law of thermodynamics, which is based on
this observation, simply states that heat flows spontaneously from a high-temperature region to
a low-temperature region. The object with the higher temperature ( more energetic) transfers
some of its energy to the low-temperature (less-energetic) object. When you put some ice cubes
in a glass of warm soda, the soda cools down while the ice warms up and eventually melts away.
You may call this “sharing resources.” Unfortunately, we as people do not follow this law closely
when it comes to social issues.
To better understand the second law of thermodynamics, consider another example. Some
of you may have young children or young brothers and sisters. If you placed the child with
some toys in a room that is tidied up and orderly, let the child play with the toys for a while,
then came back in a few minutes, you would find toys scattered all over the room in a disorderly
way. Why won’t you find toys put away nicely? Well, that is because things work spontaneously
in a certain direction in nature. These two examples demonstrate the second law of thermody-
namics. Things in nature work in a certain direction by themselves.Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀