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"Classical physics is based on three things. The first basis is that the \
phenomena that are studied are those that we can directly observe, or that we \
can describe using theories based on such things. The second basis is the \
assumption that time and distances are fixed. When we measure the passage of \
time, that measurement will be the same no matter where we make it. The same \
for distance, if we measure the length of a table top and measure the same \
table top somewhere else, the measurement will be the same. The third thing \
is that given complete information about the current properties of a \
phenomena, we can accurately predict its future and past properties; such a \
system is called ",
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".\n\tIn a very real sense we are all classical physicists\[LongDash]it is \
hard-wired into our brains. Every day we do things involving complicated \
calculations that we take for granted. We wad up paper and throw it into a \
trash can. We do this without explicitly considering trigonometry-based \
vector differential equation calculations of trajectories, gravitation, and \
air-resistance. It is built-in. As we get more advanced, even in classical \
physics, some ideas come out that require us to re-wire our brains.\n\tIn \
fact, we can state that the purpose of physics education is to promote this \
necessary rewiring to occur. How do you learn physics? Learn the facts as you \
learn the techniques to acquire them. Do not read this book in sequence, \
allow yourself to jump around. Following chapter one, all chapters and some \
sections will list prerequisites. Some of these will be other sections, some \
will be topics you should already know and are summarized in the appendices, \
and some will be techniques that are too esoteric for the primary thrust of \
the book and are also in the appendices. You should read actively and ask \
yourself questions and try to answer them. Work the exercises, problems, and \
projects that interest you. Those marked with an * are considered to be very \
important. I recommend doing one project for every Part of the Book.\n\tThe \
fundamental ideas of classical physics are intuitively known to us, but \
explaining them is difficult. Explicitly performing the calculations we make \
intuitively can be enormously difficult. One task of this book is to give you \
the tools to make such calculations.\n\tThe first topic to study is that of \
motion, what we call ",
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". This begins with the tools to describe motion, including elementary \
calculus\[LongDash]the mathematics that allows us to represent changes. We \
will then turn to the causes of motion. After examining several cases of how \
classical mechanics can predict motions, we will abstract these cases to the \
laws of ",
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"\[LongDash]these laws specify that certain quantities do not change within \
a closed system.\n\tWhat is a closed system? A closed system is a bit of a \
haphazard thing at this point. For now we can think of it as a system where \
nothing of importance to us enters it or leaves it.\n\tThe beginning of what \
we think of as physics was the work of the great physicists Galileo Galilei, \
Johannes Kepler, and Sir Isaac Newton. Kepler took the astronomical \
observations of Tycho Brahe and analyzed them to determine the laws that \
govern the motion of the planets around the Sun\[LongDash]called Kepler\
\[CloseCurlyQuote]s laws. Galileo performed experiments that established the \
properties of falling bodies and the principle that unless you push on it \
some way, an object will travel in a straight line and at constant speed (the \
law of inertia). Newton wrote out the principles of classical mechanics, \
optics, and gravitation. This laid the groundwork for rapid progress in \
classical mechanics. This became a program in its own right.\n\tThe program \
was to derive, one way or another, a force law. A force is understood to be \
something that pushes or pulls. A force law is then some way of \
mathematically describing a specific force. Once you had a force law you \
could use Newton\[CloseCurlyQuote]s laws of motion to derive an equation \
describing the changing states of motion\[LongDash]what we call a \
differential equation. Once this equation is solved, then you can predict all \
future motion of the system you are studying.\n\tFollowing this program, \
progress was rapid! Newton only identified a single force law in his work, \
that was the force of gravity. This technique allowed him to derive Kepler\
\[CloseCurlyQuote]s laws mathematically. It also allowed him to discover the \
first known unification of the laws of physics. He equated the fall of an \
apple with the fall of the Moon around the Earth. The Moon falls around the \
Earth? Yes, it does, and we will get to that in time. \
Newton\[CloseCurlyQuote]s laws of motion predict a whole host of phenomena, \
they are very powerful! In fact for a long time it was thought that his laws \
were so powerful that the term ",
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" was developed to describe the entire world, and it was believed that \
Newtonian mechanics led the way to its description.\n\tJames Joule made the \
next significant discovery, that of energy. He learned that there is a \
quantity, just a number, that is related to force, that we call energy. It \
turns out that if we determine this quantity at one time, then no matter what \
we do the number will not change. This is called the ",
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". Folowing this a whole new branch of physics was invented to describe the \
effects of energy, and the nature of energy within matter. This is called ",
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" and its immediate application was the first accurate description of heat.\n\
\tAt the same time experiments were being done that unlocked some of the \
principles of electricity. Magnetism had been studied since the Middle Ages. \
Hans Oersted and Thomas Faraday discovered the laws that connected \
electricity and magnetism; namely that electricty in a coil around an iron \
rod induces magnetism in the rod, while moving a magnet through a coil of \
wire induces electricity in the wire.\n\tIt fell to James Maxwell to make the \
second great unification of physics. He found the equations that linked \
electricity, magnetism, and light. This unification forged the connection \
that made electricity, magnetism, and light different aspects of the same \
thing. That light waves were the device that propagates the electric and \
magnetic fields through a substance that did not react with anything, called \
the luminiferous ether. This was a great theory! It explained many things, \
and made many predicitions. It established the wave theory of light and led \
to many applications including radio."
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