The general study of the relationships between motion, forces, and energy is called mechanics. It is a large field and its study is essential to the understanding of physics, which is why these chapters appear first. Mechanics can be divided into sub-disciplines by combining and recombining its different aspects. Three of these are given special names.
Motion is the action of changing location or position. The study of motion without regard to the forces or energies that may be involved is called kinematics. It is the simplest branch of mechanics. The branch of mechanics that deals with both motion and forces together is called dynamics and the study of forces in the absence of changes in motion or energy is called statics.
The term energy refers an abstract physical quantity that is not easily perceived by humans. It can exist in many forms simultaneously and only acquires meaning through calculation. A system possesses energy if it has the ability to do work. The energy of motion is called kinetic energy
Whenever a system is affected by an outside agent, its total energy changes. In general, a force is anything that causes a change (like a change in energy or motion or shape). When a force causes a change in the energy of a system, physicists say that work has been done. The mathematical statement that relates forces to changes in energy is called the work-energy theorem.
When the total of all the different forms of energy is determined, we find that it remains constant in systems that are isolated from their surroundings. This statement is known as the law of conservation of energy and is one of the really big concepts in all of physics, not just mechanics.
The first few chapters of this book are basically about these topics in this order…
There may be other schemes, but for purposes of this book there are basically three types of motion.
The chapters in the section of this book about mechanics are basically arranged in this order…
Are there additional types of motion? Well, it depends on whom you ask and when you ask them. All motion is basically translational to some extent; that is to say, you can't be moving unless you (or a part of you) moves from one place to another. There is possibly a fourth type of motion that goes nowhere in the long run (not intentionally, anyway) and yet does not require that the object ever return to a particular location.
Prior to the Renaissance, the most significant works in mechanics were those written in the Fourth Century BCE by the Greek philosopher Aristotle of Stagira (384–322 BCE) — these were Mechanics, On the Heavens, and The Nature or in Greek Μηχανικά (Mekhanika), Περί Ουρανού (Peri Uranu), and Φυσική Ακρόασις (Fysike Akroasis). Although the first section of every general physics textbook is about mechanics, Aristotle's Mechanics probably wasn't written by him and won't be discussed here. On the Heavens will be discussed later in this book.
The Nature is Aristotle's work that's most relevant to this book. That's because it's the origin of the word physics. The full name Φυσική Ακρόασις (Fysike Akroasis) translates literally to "Lesson on Nature" but "The Lesson on the Nature of Things" is probably more faithful. The Nature acquired great stature in the Western world and was identified almost reverently by academics as Τὰ Φυσικά (Ta Fysika) — The Physics. In this book Aristotle introduced the concepts of space, time, and motion as elements in a larger philosophy of the natural world. Consequently, a person who studied the nature of things was called a "natural philosopher" or "physicist" and the subject they studied was called "natural philosophy" or "physics". Incidentally, this is also the origin of the words "physician" (one who studies the nature of the human body) and "physique" (the nature or state of the human body).
Aristotle professed many things about the physical world and certainly was a great thinker for his time. Unfortunately his scientific statements are usually wrong — sometimes comically. The English philosopher Bertrand Russell (1872–1970) compiled a list of Aristotle's worst offenses in his 1943 essay An Outline of Intellectual Rubbish.
Aristotle, in spite of his reputation, is full of absurdities. He says that children should be conceived in the winter, when the wind is in the north, and that if people marry too young the children will be female. He tells us that the blood of females is blacker then that of males; that the pig is the only animal liable to measles; that an elephant suffering from insomnia should have its shoulders rubbed with salt, olive-oil, and warm water; that women have fewer teeth than men, and so on.
Bertrand Russell, 1943
Aristotle was a philosopher, not a scientist, He is sometimes credited as the inventor of logic. ("Invent" may be too strong a word here. Certainly without Aristotle, logic would have evolved differently.) And logic and reasoning are central to science, so it seems logical and reasonable to assume that Aristotle could have been one of the first scientists. Unfortunately, that's not the way it went. Russell said it best.
Aristotle could have avoided the mistake of thinking that women have fewer teeth than men, by the simple device of asking Mrs. Aristotle to keep her mouth open while he counted.
Science is different from other human activities. It doesn't matter what you reason yourself into logically (all swans are white), what you feel emotionally (dogs are better than cats), or what is accepted culturally (there ain't no room for sheep in cattle country). In the end, it all comes down to observation.
The statement "women have fewer teeth than men" is famous now, not because Aristotle said it, but because Russell said Aristotle said it. The original quote came from Aristotle's History of Animals, which I managed to find in both the original Greek and an English translation.
Ἔχουσι δὲ πλείους οἱ ἄρρενες τῶν θηλειῶν ὀδόντας καὶ ἐν ἀνθρώποις καὶ ἐπὶ προβάτων καὶ αἰγῶν καὶ ὑῶν· ἐπὶ δὲ τῶν ἄλλων οὐ τεθεώρηταί πω. Males have more teeth than females in the case of men, sheep, goats, and swine; in the case of other animals observations have not yet been made Aristotle, ca. 350 BCE
How astoundingly ironic.
This sorry state of affairs persisted in the Western world for roughly a millennium and half. It took an Italian from Pisa Galileo Galilei (1564–1642) to show the world how to see.