Newtons Third Law
Introduction
Newton's Third Law, also known as the law of action and reaction, is a fundamental principle in physics that states for every action, there is an equal and opposite reaction. This law is one of the three laws of motion formulated by Sir Isaac Newton, a 17th-century English mathematician and physicist.
Historical Context
Newton's Third Law was first published in his work "Philosophiæ Naturalis Principia Mathematica" in 1687. The law, along with his other two laws of motion, laid the groundwork for classical mechanics, which dominated the scientific view of the physical universe for the next three centuries.
Statement of the Law
The formal statement of Newton's Third Law is: "To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts." This means that any force exerted on a body will create a force of equal magnitude but in the opposite direction on the object that exerted the first force.
Explanation and Examples
To understand Newton's Third Law, consider the example of pushing a wall. When you push the wall, the wall pushes back with an equal amount of force. This is why you can feel resistance when you push the wall. The force you exert on the wall and the force the wall exerts on you are action-reaction force pairs.
Another common example is the recoil of a gun. When the bullet is fired (action), the gun is pushed backward (reaction). The force propelling the bullet forward is equal to the force pushing the gun backward.
Mathematical Formulation
In mathematical terms, Newton's Third Law can be expressed as F₁₂ = -F₂₁. Here, F₁₂ represents the force exerted by object 1 on object 2, and F₂₁ is the force exerted by object 2 on object 1. The negative sign indicates that these two forces are in opposite directions.
Applications
Newton's Third Law has wide-ranging applications in various fields of science and engineering. For example, it explains how rockets and jet engines work. The rocket's engine pushes gas out, and in reaction, the gas pushes the rocket in the opposite direction. This principle is known as rocket propulsion.
In the field of structural engineering, Newton's Third Law helps in understanding how structures can withstand forces and remain in equilibrium.
Misconceptions and Clarifications
A common misconception about Newton's Third Law is that the action and reaction forces cancel each other out. However, this is not the case because they act on different bodies. For instance, in the case of a flying bird, the downward force exerted by the bird's wings on the air (action) is equal and opposite to the upward force exerted by the air on the bird (reaction), allowing the bird to fly.