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The Laws of Motion were formulated by Sir Isaac Newton in the 17th century and are fundamental principles that describe the motion of objects. These laws form the basis of classical mechanics and are still widely used to understand and predict the behavior of objects in motion. Newton's three laws of motion are:

1. Newton’s first law: the law of inertia

Newton’s first law states that if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force.

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Newton’s second law: Law of Acceleration

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Newton’s second law: Law of Acceleration

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Newton’s second law is a quantitative description of the changes that a force can produce on the motion of a body. It states that the time rate of change of the momentum of a body is equal in both magnitude and direction to the force imposed on it. The momentum of a body is equal to the product of its mass and its velocity. Momentum, like velocity, is a vector quantity, having both magnitude and direction. A force applied to a body can change the magnitude of the momentum or its direction or both. Newton’s second law is one of the most important in all of physics. For a body whose mass m is constant, it can be written in the form F = ma, where F (force) and a (acceleration) are both vector quantities. If a body has a net force acting on it, it is accelerated in accordance with the equation. Conversely, if a body is not accelerated, there is no net force acting on it.

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Newton’s third law: the law of action and reaction

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Newton’s third law: the law of action and reaction

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Newton’s third law states that when two bodies interact, they apply forces to one another that are equal in magnitude and opposite in direction. The third law is also known as the law of action and reaction. This law is important in analyzing problems of static equilibrium, where all forces are balanced, but it also applies to bodies in uniform or accelerated motion. The forces it describes are real ones, not mere bookkeeping devices. For example, a book resting on a table applies a downward force equal to its weight on the table. According to the third law, the table applies an equal and opposite force to the book. This force occurs because the weight of the book causes the table to deform slightly so that it pushes back on the book like a coiled spring.

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In a 2019 article for Behavioral Economics, Aline Holzwarth, a behavioral scientist, used Newton’s laws of motion to inform three laws of human behavior.

These three laws are:

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1. Behavior tends to follow the status quo unless it is acted upon by a decrease in friction or increase in fuel.

2. Behavior (B) is a function of the person (P) and their environment (E), or B=f(P,E).

3. For every decision made, there are tradeoffs and the potential for unintended consequences.

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1. Inertia: Both physical objects and individuals tend to maintain their current state—either at rest or in motion—unless acted upon by an external force.

2. Action and Reaction: Analogous to Newton's Third Law, human interactions often exhibit a reciprocity where actions from one person may generate equal and opposite reactions from others.

3. Forces and Motivations: Just as force in physics produces changes in motion, human actions are often driven by motivations that can influence the direction and intensity of behavior.

4. Conservation of Energy: While not explicitly named in Newton's laws, the concept of conserving energy finds a metaphorical parallel in human behavior, where individuals allocate and conserve mental and emotional energy in decision-making and daily activities.

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The differences between the Laws of Motion and the Laws of Human Behavior are clear. The Laws of Motion deal with how things like objects and forces interact in a straightforward, mathematical way. On the other hand, the Laws of Human Behavior are about the complicated and varied nature of people, taking into account emotions, thoughts, and social factors.

The Laws of Motion can be precisely expressed using math, making predictions possible in controlled situations. In contrast, understanding human behavior involves subjective and qualitative aspects, making it more challenging to measure and predict.

While physical laws offer accurate predictions in specific conditions, human behavior is more unpredictable and depends heavily on various factors like culture and individual differences.

Human behavior is subjective and varies from person to person and across different cultures, unlike the objective and universal nature of the Laws of Motion.

While the Laws of Motion remain constant, human behavior is flexible and adaptable, allowing for changes based on experiences and the environment.

Ethical and moral considerations are a significant part of human behavior, a dimension not present in the Laws of Motion, which focus solely on physical interactions.

Laws of Motion typically look at isolated forces, while human behavior is influenced by a mix of psychological, social, cultural, and environmental factors.

Human behavior involves conscious decision-making and intentionality, aspects that are absent in the deterministic nature of the Laws of Motion, which simply describe physical interactions.

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This article was most recently revised and updated by

Newton's second law is a quantitative description of the changes that a force can produce on the motion of a body. It states that the time rate of change of the momentum of a body is equal in both magnitude and direction to the force imposed on it. The momentum of a body is equal to the product of its mass and its velocity. Momentum, like velocity, is a vector quantity, having both magnitude and direction. A force applied to a body can change the magnitude of the momentum or its direction or both. Newton's second law is one of the most important in all of physics. For a body whose mass m is constant, it can be written in the form F = m a, where F (force) and a ( acceleration) are both vector quantities. If a body has a net force acting on it, it is accelerated in accordance with the equation. Conversely, if a body is not accelerated, there is no net force acting on it.

Newton's third law: the law of action and reaction

Newton's third law states that when two bodies interact, they apply forces to one another that are equal in magnitude and opposite in direction. The third law is also known as the law of action and reaction. This law is important in analyzing problems of static equilibrium, where all forces are balanced, but it also applies to bodies in uniform or accelerated motion. The forces it describes are real ones, not mere bookkeeping devices. For example, a book resting on a table applies a downward force equal to its weight on the table. According to the third law, the table applies an equal and opposite force to the book. This force occurs because the weight of the book causes the table to deform slightly so that it pushes back on the book like a coiled spring.

If a body has a net force acting on it, it undergoes accelerated motion in accordance with the second law. If there is no net force acting on a body, either because there are no forces at all or because all forces are precisely balanced by contrary forces, the body does not accelerate and may be said to be in equilibrium. Conversely, a body that is observed not to be accelerated may be deduced to have no net force acting on it.

Influence of Newton's laws

Newton's laws first appeared in his masterpiece, Philosophiae Naturalis Principia Mathematica (1687), commonly known as the Principia. In 1543 Nicolaus Copernicus suggested that the Sun, rather than Earth, might be at the centre of the universe. In the intervening years Galileo, Johannes Kepler, and Descartes laid the foundations of a new science that would both replace the Aristotelian worldview, inherited from the ancient Greeks, and explain the workings of a heliocentric universe. In the Principia Newton created that new science. He developed his three laws in order to explain why the orbits of the planets are ellipses rather than circles, at which he succeeded, but it turned out that he explained much more. The series of events from Copernicus to Newton is known collectively as the Scientific Revolution.

In the 20th century Newton's laws were replaced by quantum mechanics and relativity as the most fundamental laws of physics. Nevertheless, Newton's laws continue to give an accurate account of nature, except for very small bodies such as electrons or for bodies moving close to the speed of light. Quantum mechanics and relativity reduce to Newton's laws for larger bodies or for bodies moving more slowly.

The Editors of Encyclopaedia Britannica Erik Gregersen.

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Newton's laws of motion - Momentum, Action-Reaction, Net Force

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Newton's second law is a quantitative description of the changes that a force can produce on the motion of a body. It states that the time rate of change of the momentum of a body is equal in both magnitude and direction to the force imposed on it.

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Key points

The unified theory of psychology frames human behavior in terms of three factors: investment, influence, and justification.

Investment frames animal behavior patterns in terms of work effort that emerges because of evolution and learning.

Influence refers to how different individuals impact each other and relate in competitive and cooperative ways across systems.

Justification refers to how human persons organize and legitimize their activity based on networks of propositions.

What is the best way to frame human behavior? According to the unified theory of psychology ¹, we can think of human beings as: (a) animals engaged in "behavioral investments" who are also (b) primates engaged in social influence in a relational matrix who are also (c) persons engaged in justifications in a sociocultural context.

To see these three vectors, consider a lawyer engaged in the defense of her client. First, we can track the lawyer's behavioral investments. We can track these in terms of both what the lawyer is doing and in terms of the neurocognitive processes associated with those actions. Things like walking, getting dressed, eating, and going to the bathroom are all "basic" behavioral investment patterns. We can frame such actions in terms of goal-directed activity, where the individual is moving from the current state to the desired state. This is the "path" of behavioral investment. Using the excellent work of cognitive scientist John Vervaeke and his colleagues, we can frame the neurocognitive processes associated with choosing such a path via what Vervaeke calls "recursive relevance realization." Put in common language, this means that the individual is scanning the environment for what is relevant to realize her goals and that there is a constant, recursive pattern that is modeling both this process and other potentially relevant goals, pathways, risks, or constraints.

Ultimately, according to the unified theory of psychology, we can frame the principles that make up the "law" of behavioral investment in terms of (a) energy economics; (b) evolution; (c) behavioral genetics; (d) neurocomputational control in the organism; (e) learning; and (f) developmental life history. To give just one example of how we can apply these principles to the behavior of the lawyer, we posit that when the lawyer parks her car outside the courthouse, she will intuitively take the "path of least effort" to get to the courtroom. This is an example of the principle of energy economics at play.

The social and relational matrix consists of the way human behavior investments and values affect their relational world. Regarding the lawyer, we can place her in a socio-ecological network of relations that started even prior to her being born. For example, we can wonder whether her parents embraced her mother's pregnancy or not. The fact that she may have been named well before her birth points to the primacy of this relational network-it exists even prior to the specific human being. We can then place her in nested "spheres of influence and ecology," such that we can see the kinds of relationships she had over time with her: (a) family of origin; (b) peers and friends; (c) romantic partners, and (d) groups. We can then nest those relational dynamics in the larger community and professional contexts, and then even larger cultural contexts, such as the fact that she lives in the United States and identifies as a Christian.

The primate world of social influence can be first framed in terms of the way in which an individual's actions influence the behavior investments of other individuals. However, in social primates like humans, evolution has prepared us with a rich relationship system that frames our motivations and emotions in the relational world. According to the unified theory, we can frame this "law of influence" by the way we track our level of social influence and relational value and examine how that reverberates in the social sphere. Social influence refers to the extent that we can influence others according to our interests, and relational value refers to the extent to which we are known and valued by important others. In addition, our relational system tracks the way we relate to others on the dimensions of "competitive power" framed by the relational poles of dominance and submission, "cooperative love" framed by the relational poles of affiliation and hostility, and "freedom and engagement" framed by the relational poles of autonomy and dependence.

Applied to the lawyer, she is trying to influence her client, the judge, and the jury to act in a way that results in an acquittal. These are the instrumental aspects of influence. Of course, we can also explore how she felt in terms of relational value, and we can examine the processes of competitive power, cooperative love, and freedom versus dependency.

Other animals invest and influence each other in systematic ways, but only humans engage in the third law, which is justification. Processes of justification emerge with propositional language, and humans are the only known animal that builds justification systems. These are systems of knowledge that humans construct to determine what is the case and what ought to be the case.

The laws that humans develop are great examples of systems of justification. Indeed, these are the formalized systems of justification that connect the rules of society to the institutionalized power structures, such as a police force and the corrections system. This highlights that, in addition to systems of justification, humans have also evolved our technologies in a manner that is radically different than other animals. Together, justification systems and technological evolution make human societies unique compared to other animals.

The lawyer is someone who operates on the culture-person plane of existence. She lives in a context of justification that ties together the relational world (see diagram below). Broadly defined, justification processes are ubiquitous, as they structure the implicit rules of conversation, rhetoric, and action. Of course, as a lawyer, she is engaged in the explicit process of justification as her job. A lawyer can be described as a professional justifier. Her job is to know the history and processes of formal, legal justification procedures that channel people into categories like "guilty" and legitimize sanctions, going all the way to putting someone to death in some cases. Here we see the "law" of justification as literally framing the laws of human behavior and the behavior of lawyers.

The bottom line is that investment, influence, and justification are powerful ways to describe and explain human behavior. Indeed, they are so powerful that they might constitute "laws," at least in a general dynamic sense of being up to the task to frame the complexities of human activity.

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Framing human behavior in terms of investment, influence, and justification.

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The Basic Idea

Theory, meet practice

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If you took physics in high school, you're familiar with Newton's three laws of motion. These rules describe the relationship between the motion of a body and the forces acting on it, and were first proposed in the 17th century by English mathematician Isaac Newton.¹ Remarkably, Newton managed to distill complex and difficult physical concepts into three simple, universal rules.

The three laws of motion are:

1. A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force.

2. The force acting on an object is equal to the mass of that object times its acceleration.

3. For every action, there is an equal and opposite reaction.

Until Newtonian physics was displayed by quantum mechanics and general relativity in the early 20th century, these laws were thought to describe how all objects and their motion are impacted by forces. They are still used frequently in calculations and do reflect the motion of objects accurately - unless we are talking about quantum particles or extremely massive bodies. But can we apply these laws to anything else? In a 2019 article for Behavioral Economics, Aline Holzwarth, a behavioral scientist, used Newton's laws of motion to inform three laws of human behavior.²

These three laws are:

1. Behavior tends to follow the status quo unless it is acted upon by a decrease in friction or increase in fuel.

2. Behavior (B) is a function of the person (P) and their environment (E), or B=f(P,E).

3. For every decision made, there are tradeoffs and the potential for unintended consequences.

Although human behavior is complicated, Holzwarth suggested that these laws can at least capture very general behavioral tendencies.

"

And just as Newton's Laws describe the motion of physical objects, these Laws of Human Behavior aim to provide a general model for how humans behave. People tend to stick to the status quo unless the forces of friction or fuel push us off of our path; behavior is a function of the person and their environment; every decision includes tradeoffs and the potential for unintended consequences.

Theory, meet practice

TDL is an applied research consultancy. In our work, we leverage the insights of diverse fields-from psychology and economics to machine learning and behavioral data science-to sculpt targeted solutions to nuanced problems.

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Other social scientists have compared psychological and sociological tendencies to the universal laws of physics, but Holzwarth is responsible for drawing three clear laws from Newton's laws. ³ Like the laws of motion, Holzwarth's three laws of human behavior set out to describe behavior at large and can break down in specific instances. Although Newton's theories were ultimately replaced by quantum mechanics and relativity, the three laws of motion continue to be helpful outside of bodies of mass that are either extremely large or small. Similarly, the laws of human behavior could be most powerful when used as approximations of general tendencies.

The first law says that behavior tends to follow the status quo unless it is acted upon by a decrease in friction or increase in fuel. Holzwarth summarises this law in a concept we are all probably familiar with: humans tend to take the path of least resistance. When we let our "autopilot" take control of our decisions, like making a healthy meal versus ordering in, our automatic response will be to choose the most convenient option - even if it is a poor choice in the long run. This behavior is captured by the Status Quo Bias, which describes our preference to continue what we are doing. Even if it makes sense to make a change, like walking to work instead of driving to get more exercise, we are naturally resistant to switching up our routine.

Similar to inertia in Newton's first law of motion, the status quo bias stands in the way of changing our behavior. We need a certain amount of force for a change to take place. Indeed, inertia has actually been defined in behavioral science due to our resistance to change. Holzwarth describes two primary kinds of forces that determine human behavior: friction and fuel. Friction is a negative force because it acts as an obstacle to performing a behavior. For example, friction can be the phone call we need to make to make a doctor's appointment, or the line we have to stand in to renew our driver's license.

This means that changing our behavior is often quite hard, unless the other primary force, fuel, can overpower the friction in a situation. Fuel makes behaviors more appealing, like social and monetary rewards for completing certain tasks (i.e. going to work). Whether or not we can change our behavior depends on the balance of fuel and friction.

The second law of human behavior, analogous to the law behind the famous F = ma relationship in physics, suggests that behavior (B) is a function of the person (P) and their environment (E), or B=f(P,E). Holzwarth explains that behavior depends on the particular person and their personal values, beliefs, experiences, etc., along with the specific environment the person finds themself in. This includes the physical environment, sensory elements, their social circle, and any other external factors. One clear example of the influence of our environment on behavior is in-store displays and layouts, like the candy and small snacks located in the check-out aisle of a store. While customers are waiting, they may be tempted to pick up a chocolate bar since it is in front of them, even if their personal factors (hunger, health conscientiousness) are not particularly in favor of buying one.

The equation B=f(P,E) is not Holzwarth's creation, but goes back to one of the pioneers of modern social psychology, Kurt Lewin. He first proposed this universal relationship in 1936, emphasizing the importance of the interaction between a person and their environment in determining their behavior.⁴ Holzwarth also emphasizes that in B=f(P,E), behavior is determined not by the person and environment in isolation from each other, but by how the person reacts to their environment. Although we have the tendency to underestimate the influence of situational factors on a person's behavior due to a bias called the fundamental attribution error, the second law of human behavior serves as a reminder that we need to understand both the person, the environment, and their interaction to explain behavior.

The third law (based on the concept that when two bodies interact they apply forces to one another that are equal in magnitude and opposite in direction) is that for every decision made, there are tradeoffs and the potential for unintended consequences. This may be the most general and seemingly obvious of the laws, but Holzwarth argues that we often do not consider the tradeoffs and unintended consequences of our decisions. For example, with the traditional pros and cons approach to decision-making, we can overlook the opportunities we lose by choosing a particular option, also known as the opportunity cost. If we decide to buy a healthy salad for lunch everyday at work, we lose the opportunity to spend that money on other health-related foods or treatments.

Another part of decision-making that we often overlook are unintended consequences. These are the results we do not see coming, whether they affect us or not. On a global scale, harmful ecological effects are common unintended consequences of behaviors. Even well-intentioned social movements can have unexpected negative impacts on the cause they are trying to address. For instance, consider the consequences of a plastic straw ban. It seems like a clear solution to reduce plastic waste and negative environmental effects. Yet, banning plastic straws removes the weight of making an environmentally-friendly decision off of the consumer, thereby taking away the mental effect of customers consciously considering their impact on the environment. As a trickle-down effect, consumers may be less thoughtful of the environmental effect of their other choices, and will not internalize the environmental message behind the popular movements which drove the bans in the first place.

Consequences

These laws provide a very basic and broad framework with which to understand our behavior and that of those around us. Holzwarth incorporates a number of well-established biases and heuristics underneath her three main laws, effectively capturing many important concepts in behavioral science. As Holzwarth notes is her intention, the laws do not present anything new but instead consolidate a multitude of ideas in the field into these general rules. For the average person, these may be a more friendly reminder of our tendencies than a long list of individual biases.

In this way, the laws act similarly to their analogues in physics - they distill a field of complex theories into three simple laws. Holzwarth's aim is that the laws of behavioral science can inform how we design products. Just as Newton's laws continued to be used for calculations and understanding the motion of most objects, these laws can hopefully serve as a tool to form products and services based on our behavior. Even if there are specific instances where these laws no longer hold true, as is the case when Newton's laws are applied to quantum particles or extremely massive objects, these generalizations can nevertheless lead us to better apps and programs.

Controversies

Laws in behavioral science have to be very general as a rule, and even so, human behaviors can always fall outside a specific law - unlike how we expect physical matter to adhere to certain laws. As psychology is considered a "soft" science, the field is generally averse to theorizing fundamental rules that govern behavior. Moreover, it may seem a little forced to try to translate Newton's laws of motion into similar laws for human behavior. That said, the laws do feel intuitive once Holzwarth explains them, and like Newton's laws, appear to be obvious even if we were not able to form the connections before reading about them.

Other questions Holzwarth addresses are: why create these laws now? Are they really that helpful? Holzwarth suggests that behavioral science as a field is currently undergoing a parallel change to the transformation of physics during Newton's time. Advances were happening rapidly, fuelled by the demand for industrial applications from physics. Similarly, Holzwarth argues, there is currently a serious necessity for innovative and competitive companies to incorporate behavioral science insights not only for marketing and management purposes, but for domains such as product development, healthcare, and banking. As a result, there is a need for behavioral scientists to communicate and organize their work in a way that others can understand and apply to their own respective fields. These laws serve as an effective guide for generalized human behavior, and incorporate many well-established theories, biases and heuristics within them.

In the same way that Newton's theory of gravity and laws were overturned in the 20th century by quantum mechanics and relativity but still continue to be used as helpful tools for approximate calculations, the three laws of human behavior have the greatest potential as a guide for professionals both familiar and unfamiliar with behavioral science to develop better products. Human behavior is known to be complex and varied, but it nevertheless often follows certain rules, just like physics. These generalizations can help us understand our own behavior at least in part and even more so help us understand the behavior of those around us.

Related TDL Content

The Status Quo Bias describes our resistance to change, or our preference for the current state of affairs. This bias frees up our mental resources for other tasks, but small decisions we relegate to our "auto-pilot" can fall prey to the status quo bias over and over, resulting in little change even when we do want it. Read more about the status quo bias in our reference guide.
Inertia
Inertia refers to an object's tendency to resist a change in motion. As the first law of human behavior suggests, people also resist change and prefer to stick with the status quo. As a result, behavioral scientists have studied inertia in terms of our tendency to continue interpreting information the same way. This reference guide entry describes the history of inertia as a behavioral science concept, and how we can apply this physical idea to how cognition works.
Why is Changing Behavior So Hard?
This article explores the power and frequent irrationality of our resistance to change. Often, regardless of how we feel about a choice, we will avoid making a change, as the first law of human behavior describes. No matter how attractive a behavior is, if the friction blocking the behavior is stronger than the fuel, we will resist change.
Fundamental Attribution Error
This bias occurs when we make judgements about another person's behavior and disproportionately attribute their actions to their personality more than situational factors. As the second law of human behavior indicates, a person's behavior is determined by the interaction between a person and their environment. Both personal and situational factors are important, and critically, a person's unique reaction to their surroundings will determine their behavior.
The Banned Wagon: Are Bans the Best Way to Solve the Plastic Problem?
In this article about the pros and cons of plastic straw bans, Holzwarth's third law is on full display. Although banning straws would clearly reduce plastic waste, the opportunity cost means that consumers lose the opportunity to make conscientious decisions about their environmental impact. This can also be seen as an unintended consequence, where bans essentially make the choice for the consumer, meaning that they are less encouraged to think about their environmental impact in other situations.

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The Three Laws of Human Behavior - The Decision Lab

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Aline Holzwarth used Newton's laws of motion to inform three laws of human behavior, which can at least capture very general behavioral tendencies.