Classical mechanics is the study of how things move in relation to force. Unsurprisingly, it was the first branch of physics discovered, and it is the foundation of all the other branches. Its principles were codified by Newton in a book called the Principia; hence, classical mechanics is sometimes referred to as Newtonian mechanics.
There are three basic laws of motion. The first is the law of inertia, which says that an object at rest will remain so, unless acted on by another force; conversely, an object in motion will remain so, unless acted on by another force. Obviously, it would be highly unusual to see a stationary object suddenly spring to life and start moving on its own, so we don’t generally have trouble with the concept of inertia as it relates to objects at rest. Nevertheless, the idea that an object will remain in motion unless acted upon by another force is somewhat counter-intuitive, because our everyday human experience confirms that moving objects tend to come to a standstill. In reality, it is the net force of friction that causes such objects to come to a standstill; if you somehow managed to propel an object into the vacuum of space, it would maintain its velocity until it ran into an unbalancing force, such as a planet or a comet.
Newton’s second law says that the net force of an object is the product of its mass and acceleration. Whereas the first law deals with balanced forces, the second law deals with forces that are not balanced. You could say that it is not really a law per se as much as it is a statement of the relationship between force, mass, and acceleration. At any rate, the relationship says that as mass increases, acceleration decreases; as force increases, acceleration increases. None of this is surprising, for it is part of our everyday experience that it is more difficult to change the direction and speed of larger objects than smaller ones. By the way, the concept of momentum is closely related to the second law because the second law measures the rate of change of momentum. Expressed as a mathematical formula, momentum is the product of mass and velocity, so that the more mass an object has, the more velocity it will have.
Newton’s third law says that every action has an equal and opposite reaction. Newton’s third law is one of those ideas that only seems obscure until it is illustrated with examples. So, let’s look at a couple examples. Consider how fish swim. They use their fins to push the water backwards, whereupon the water exerts an equal and opposite force that propels the fish forward. Or consider how a rocket works. It expels gas, smoke, and flames in a downward direction so that it can propel itself in an upward direction: a classic instance of Newton’s third law.
Of course, classics mechanics has been superseded by special relativity. But it remains useful because it is still extremely accurate in predicting the behaviour of most objects that are not smaller than a molecule, similar to how it is possible to predict the movement or behaviour of masses of people but not individuals.
Are the concepts of classical mechanics useful outside the domain of physical science? My answer is yes. Human behaviour can be understood in terms of classical mechanics; the moral universe seems to operate by analogous laws. Consider inertia. Like any object in the physical world, human behaviour tends to stay at rest. Ortega, who was a Spanish philosopher of the 20th century, wrote that we refer to the crowd as “masses” not so much because of their multitude, but because of their inertia. Inertia is why we hate change. It is also why remarkable people are so few.
As for the second law of motion, all of us recognize something like momentum in the course of our everyday lives. Often, we literally say that we are “gaining momentum.” But what is momentum as it pertains to the moral dimension? In short, it is the force that flows from the past into the present, which either helps us succeed or hinders our progress. Winners tend to win, and losers tend to lose, partly because of the momentum of past victories or past failures. It’s been said that habit is second nature, but what is habit except a combination of the power of inertia and the momentum generated by one’s past actions?
Many things seem possible when you have momentum behind you; few things seem possible when you don’t.
There is, also, a moral equivalent to Newton’s third law, the law of action and reaction. Anyone who has ever tried to achieve great things has encountered oppositional force, which typically takes the form of temptation, self-sabotage, and the like. The moral universe, like our physical universe, does not exist in the vacuum of space, so it is not enough just to act once, and then to rest on one’s laurels. Rather, it is necessary to exert oneself until the bitter end, and that will always be the case so long as moral “friction” is a permanent feature of our lives. Indeed, there is no way to avoid oppositional force except to yield to it, which gets you precisely nowhere.
We could look at the third law from a different angle. Lao Tse wrote that “if you keep stretching a bow, you repent of the pull.” To this we might add if you stretch a bow long enough you will warp it, which destroys into ability to convert potential energy into kinetic energy. Similarly, one’s “potential” in life is eventually lost if one does not convert it into actual achievement.
It takes discipline to change your behaviour, to be sure, but it is not at all clear where the power to do so comes from. Some kind of force is necessary to get things off the ground, and momentum helps to keep it going. But from what inner store do we draw to overcome oppositional force? It is, after all, relentless, inexhaustible, and incessant. There is a mystery here. One thing is for sure: we cannot rely on anyone but ourselves.