Introduction to Newton’s Third Law
Giving a very simple statement about motion, Newton hyped the concept of motion classically. The statement ‘For every action, there is an equal and opposite reaction ’, is more like a phrase recited by every student in small classes. It simply and beautifully describes the effect of friction. The physics lying under collision, movement, push or a pull is well-covered by the topic. According to the theory, an object acts on something with an action force which instantly shows a reaction force opposite to the original one.
Newton’s Third Law of Motion has ruled classical mechanics. This fundamental principle gives the mechanism of two bodies dealing physically. Though being straightforward, its superiority is at the next level, leading daily activities to complex aeronautical terms. Cosmic phenomena also somewhat behave according to Newton’s third law. Understanding Newton’s Third Law also gives the concept of nature and our relationship with the surrounding.
Understanding Action and Reaction Forces
Newton’s Third Law appears in the dual nature called action and reaction forces. These forces show up with the same magnitudes but act in opposition. The action of one object on the other excites the other object to react. When an object A acts with a certain force on object B, object B, at the same time, generates a force of equal but reverse nature on object A.
To better understand the phenomena, we can take a simple example of pushing a wall. We apply force to generate a push. In reaction, the wall pushes back at us, creating an equal amount of force. It’s important to understand that to generate action and reaction forces, two bodies are required. They cannot be experienced by the same object.
Key points for action-reaction forces:
- Equal in Magnitude: The reaction force depends on what amount of force we have applied (action force). Both have equal nature.
- Opposite in Direction: One is a cause and another is an effect and acts in the opposite direction.
- Act on Different Objects: Being opposite, they don’t cancel out, but on repulsion they show some effect.
Thus Newton’s third law points out all fundamental nature of interactions existing in nature, ranging from the microscopic scale to the astronomical scale.
Historical Context: Newton’s Formulation of the Third Law
Philosophiae Naturalis Principia Mathematica (1687) was the pioneer work of Newton, where he included all definitions and mathematical relations of force and motion. Before Newton, scientists like Galileo Galilei had made great advances in defining motion, but a complete shape of definition was missing. By studying old papers and considering interactions and symmetry, he developed the third law.
Some of the historic ideas, like that of René Descartes, were in line with the concept of Newton. He put all scattered theories into one frame and organized them systematically. Similarly, Aristotle’s physics about motion was also left backward by Newton’s theory. His ability to combine data into a larger, logical framework transformed physics and paved the way for the creation of calculus, astronomy, and much of science today.
Mathematical Representation of Action-Reaction Pairs
Newton’s Third Law contains not much mathematics. His principle can just be visualized mathematically as,
FAB=−FBA
Where:
- FAB is the action force applied by object A on object B,
- FBA is the reaction of object B employed on A.
The negative sign shows the reverse behavior of two forces.
Another way to understand it is through interaction examples. Suppose we are walking on the floor.
- The foot exerts a downward gravitational force (its weight) on the ground.
- The ground provides an upward normal force to the foot.
In ideal cases, these forces maintain equilibrium, showing the symmetry of nature. If external factors (such as acceleration) are also acting, then these additional factors must be considered. However, the action-reaction principle always holds for any two objects interacting.
Common Misconceptions About Newton’s Third Law
Being too simple, there are certain contradictions among the public. Some confusion and their proper explanations are given below:
- Action and Reaction Forces Cancel Each Other Out
Cancellation never happens if the forces are acting on different objects. So the misconception of cancellation should be erased.
- Only Moving Objects Exert Reaction Forces
As illustrated above, a resting object like a wall, bench, floor, etc., when acted upon by force, also exerts a reaction force. Thus the misconception of considering only moving objects as force generators should be removed.
- The Reaction Happens After the Action
Another misconception is that the reaction comes after the action. In truth, these forces are like twin forces, occurring in pairs and acting simultaneously.
- Heavier Objects Exert Greater Reaction Forces
Some think that heavier objects show greater reaction. In fact, the reaction force is always equal in magnitude to the action force and doesn’t concern itself with the mass.
Clearing these misunderstandings is important for building a strong base in physics education.
Real-world Examples Illustrating the Third Law
Newton’s Third Law has countless real-world circumstances. Some examples are given below:
- Walking
The walking motion is possible because of the action exerted by the foot and the reaction exerted by the ground to the foot.
- Swimming
Swimmers push water with their hands and feet. The water also provides a push to let them swim.
- Rowing a Boat
A rower rows the water backwards with the oars, and the boat transports forward due to the reaction force of the water.
- Jumping
When we press our legs against the ground, it reacts by sending us upward. The reaction force is the same as that applied by the legs.
- Rocket Propulsion
Rockets propel according to Newton’s third law. A rocket throws exhaust gases downwards, which helps it to propel upwards.
These examples show that without reaction forces, motion would not be possible.
Applications in Engineering and Technology
Like the remaining two laws, Newton’s third law is equally applied in engineering and technology. Some applications are listed below:
- Structural Engineering
In building design, the action and reaction forces of the structure and the land must be studied well for safety and strength. Beams, columns, and other sectors must be designed by checking well the impacts of these forces.
- Automotive Safety
The safety mechanisms, like airbags and brakes, absorb the forces exerted during collisions. Engineers launch these systems to scatter forces and reduce the reaction force that is likely to cause great injury.
- Robotics
Robots are accompanied by sensors to make them tackle with the surroundings. Understanding action and response mechanics helps for accurate control of movement and other handling activities.
- Fluid Dynamics and Pumps
Pumps and motors use action-reaction principles to transport fluids properly. The efficiency and stability of these systems highly rely on perfect force balance.
Newton’s Third Law in Aerospace Dynamics
Aerospace dynamics includes some of the most stunning examples of Newton’s Third Law.
- Rocketry
Rocket engines operate by pushing high-velocity gasses downward. According to the Third Law, this action produces an upward force (thrust), which raises the rocket. People often get confused that the rocket requires an atmospheric medium to propel. However, it should be noted that this interaction does not need an atmospheric medium.
The fundamental thrust equation:
F=m●ve
Where:
- m● is the mass flow rate of exhaust,
- ve is the exhaust velocity.
This equation underpins the application of Newton’s law.
- Satellite Maneuvering
Satellites frequently employ tiny thrusters to change direction or orbit. Expelling gas molecules in one direction generates a reactive force, which moves or turns the satellite accordingly.
- Aircraft Lift
Along with Bernoulli’s principle, Newton’s Third Law also plays a role in the mechanism of aircraft lifting. Air driven down by the aircraft wing produces an upward force called lift.
- Spacewalks (Extravehicular Activity)
Astronauts rely on jetpacks to travel in space. Those small units of discharged gas generate a reactive force that pushes the astronaut in the opposite direction.
The Role of the Third Law in Sports Mechanics
From winner performance to safety mechanisms, all apply Newton’s third law in sports. Some examples follow:
- Running
Racers press their feet harder to put significant stress on the track surface. The greater force they apply, the track propels them further accordingly.
- Tennis
When a tennis player hits the ball with a racket, the ball produces an equal and opposing force on the racket which throws the ball front. Players give powerful shots by effectively applying Newton’s law.
- Basketball
When players jump for a dunk, they press their legs on the court surface with a greater force, and the reactive force throws them higher.
- Boxing
When a boxer hits, the reaction acts on the arm. Thus, they practice by well understanding this response to increase punch efficiency and lower the reaction.
- Gymnastics
The athletes rely on reaction forces to flip. Exact timing and application of force enhance the resulting movement.
Sports dynamics is mainly based on the study of ground reaction forces, impulse, and momentum, which are all governed by Newton’s Third Law.
Conclusion
Newton’s Third Law is a universal law of motion. Though being too simple, its implications range from the basic — walking, swimming, playing — to the fantastic — launches into space, structural designs.
Understanding action-reaction forces helps us gain insight into the natural and artificial worlds. It underlines that interactions are always inverse but interrelated. This idea not only influences physics but also covers wider philosophies of symmetry and karma.
As technologies are evolving rigorously, allowing mankind to journey farther into space and the quantum world, Newton’s Third Law remains as a guide to instruct and enhance the technology.
References
Lenzen, V. F. (1937). Newton’s Third Law of Motion. Isis, 27(2), 258-260.
Brown, D. E. (1989). Students’ concept of force: the importance of understanding Newton’s third law. Physics education, 24(6), 353.
https://byjus.com/physics/newtons-third-law-motion/
Newton’s Third Law
Newton, I. (2017). Laws of Motion. Law of Gravitation.
Zimba, J. (2009). Force and motion: an illustrated guide to Newton’s laws. JHU Press.
