5.10
La Tercera Ley de Newton: Introducción
Cuando un cuerpo ejerce una fuerza sobre otro cuerpo, el primer cuerpo experimenta una fuerza igual en magnitud y opuesta en dirección a la fuerza que…
Cuando dos objetos interactúan, ambos experimentan una magnitud igual de fuerza que actúa en direcciones opuestas. Esta es la afirmación de la tercera ley de Newton.
Si el vector FAB es la fuerza aplicada por el objeto A sobre B y el vector FBA es la fuerza aplicada por el objeto B sobre A, entonces, matemáticamente, la tercera ley del movimiento de Newton se expresa como el vector FAB igual al negativo del vector FBA.
La fuerza ejercida por el primer cuerpo es "acción", mientras que la fuerza experimentada por él como resultado de su propia acción se denomina "reacción".
El par "acción-reacción" actúa siempre sobre diferentes objetos pero en el mismo instante. Esta ley es importante en el análisis de fuerzas en cuerpos en reposo, así como en movimiento acelerado.
Q1: What does Newton's third law of motion state?
Newton's third law states that when two objects interact, both experience equal magnitude forces acting in opposite directions. Mathematically, if object A exerts force FAB on object B, then object B exerts force FBA on object A, where FAB equals the negative of FBA. This law reveals a fundamental symmetry in nature: forces always occur in pairs.
Q2: Why don't action and reaction forces cancel each other out?
Action and reaction forces do not cancel because they act on different bodies. The force exerted by one object is the action, while the force experienced by that object is the reaction. Since these distinct forces operate on separate objects simultaneously, they cannot combine or neutralize each other, making them essential for analyzing motion.
Q3: How does Newton's third law apply to a person pushing a wall?
When a person pushes on a wall, they exert a force on the wall (action). Simultaneously, the wall exerts an equal magnitude force in the opposite direction back on the person (reaction). This demonstrates that neither body can exert force without experiencing an equal opposing force, illustrating the law's practical relevance.
Q4: What is the relationship between action and reaction in Newton's third law?
Action and reaction form an inseparable pair of forces that occur at the same instant. The action is the force exerted by the first body, while the reaction is the force experienced as a consequence of that action. Both forces are equal in magnitude but opposite in direction, and they always act on different objects or systems.
Q5: How is Newton's third law useful in analyzing forces on bodies?
Newton's third law is important for analyzing forces on bodies at rest and in accelerated motion. It helps identify the origin of forces and determine which forces are external to a system. Understanding action-reaction pairs enables accurate force analysis and prediction of how objects interact and move.
Q6: What are the two key features of Newton's third law?
First, the action and reaction forces are always equal in magnitude but opposite in direction. Second, these forces act on different bodies or systems, meaning they are distinct forces that do not act on the same object. This separation ensures the forces remain independent and do not cancel.
Q7: Why does Newton's third law represent symmetry in nature?
Newton's third law demonstrates that forces always occur in pairs and no body can exert force on another without experiencing a force itself. This symmetry shows that interactions are mutual and reciprocal. One object cannot unilaterally impose force; both participants in an interaction experience equal and opposite forces simultaneously.