Some Austrian-school economists dislike analogies from physics in economics, because they don’t regard economics as mechanical. But since human action is physical, we can understand economics better if we understand the basics of physics.
We begin with space. For human action, space encompasses distance in three dimensions. For economics, space constitutes the sites in which activity takes place. The economics of space includes three-dimensional volume as well as a location. For human purposes, spacial land is fixed relative to the earth. Space is not altered by use, but it is consumed by using its value, as reflected by its rent, over time. There is also another type of economic space in the electromagnetic spectrum, made up of frequencies that travel through three-dimensional space.
The second rudiment of the universe is time, which has two meanings, a moment and a duration. Time is not an input into production, but a dimension of all activity. An analysis that examines a phenomenon over a duration is called “dynamic,” in contrast to the static analysis of a moment.
The third universal rudiment is mass, or its synonym, matter. Mass is what takes up space and has inertia. Economics categorizes mass as land (natural resources), human beings, capital goods, and trash.
A fundamental law of physics is that of conservation, that matter (and its sibling energy) cannot be created or destroyed, but only changed in form. But there is no conservation of value. In economics, production is the creation of economic value, processing inputs to make them more desirable. Consumption is the using up of economic value. Capital goods are items that have been produced but not yet consumed.
Linear velocity is the rate of the motion of a mass object in some direction. In economics, activity has a velocity as a mass of inputs gets processed into outputs, or objects get transported. There is also angular velocity in the speed of rotation, including the velocity of money as its turnover as measured during a year. Momentum equals mass times velocity, including a velocity of zero. Human action has momentum when activity proceeds at a constant speed and direction.
However, economic dynamics involves changes in speed or direction, which is acceleration (including negative acceleration or deceleration). A fundamental equation in physics is F=MA, force equals mass times its acceleration, Newton’s second law of motion. Newton’s first law of motion is that of inertia, that a body will retain its momentum unless an external force is applied. Force makes mass objects accelerate. On earth, mass has a weight due to the force applied by gravity
In human action, force can mean either a physical action, as inputs are moved and combined, or else a coercive action by either criminals or governments. The initiation of coercive force alters what people would otherwise voluntarily do. Such forceful intervention imposes a net loss of value on society by accelerating the mass of human action into directions or speeds that reduce its net utility. The economy and society maximize well being with rules that prevent coercive force.
Newton’s third law of motion is that for every action there is an equal and opposite reaction. When one body exerts force on another body, the other body exerts an opposite force on the first body. This law is what propels a rocket, as the force of the ejected fuel makes the rocket go in the opposite direction. Economic action encounters resistance to motion, or friction, which is good if we want to walk (as without friction we would slide around), but is bad if the friction consists of obstacles imposed by coercive force.
In economics, energy is the generation of heat, light, and movement. There are many forms of energy. In physics, potential energy is mass that can be accelerated into motion, such as an object that can fall down, or molecules that can be combined to create heat and light. There is kinetic energy of motion, with the equation: e = ½ mv2. Einstein’s equation reflecting the convertibility of mass and energy is e = mc2, but that has no relevance in the human scale of action.
In physics, work is force times displacement. Applied to human action, work is done when a person applies force (human exertion and tools) to a mass to change its location or composition, even if the change is only of bits in a computer memory. Work can also be a change in the kinetic energy of a system.
Another physics concept that has been applied to economics is equilibrium, a state of constant momentum, including zero velocity, where there is no incentive or force for acceleration. In economics, equilibrium is the exhaustion of gains from trade. At the moment you pay for goods at a store, you are in equilibrium, as you do not wish to trade any more money for goods. But a moment later, you are in disequilibrium, as some goods now have more value than the money you exchange for them. Market prices and quantities move towards equilibrium to remove a shortage or surplus or to gain from extra production, consumption, and trade.
We can see that the application of physics to human action is not mechanistic, as people act on their subjective values and beliefs and psychological inclinations, but their physical action is necessarily subject to the laws and concepts of physics. F=MA applies to human action as it does to physical particles.