(The Original Words):
"For every action, there is an equal and opposite reaction."
This sounds very simple, but it hides a fundamental truth about how forces always work in nature.
đŠ What is an âActionâ and âReactionâ?
In physics, âactionâ and âreactionâ donât mean something happening after something else, like cause and effect.They happen at the same time, always.
Hereâs what it really means:
When object A pushes on object B,object B pushes back on object AÂ with the same force, but in the opposite direction.
đ° The two forces are:
Equal in magnitude
Opposite in direction
Act on different bodies
They are like a pair of forces, and you cannot have one without the other.
𧲠Example: Pushing a Wall
When you push a wall with your hand:
Your hand applies a force on the wall.
The wall pushes back on your hand with the same force.
If the wall didnât push back, your hand would just fly through it.
đ Example: Rocket Propulsion
Rocket throws out gas backward â gas pushes rocket forward.This is not magic â the force on the gas is equal and opposite to the force on the rocket.
Action: Rocket pushes exhaust backward.
Reaction: Exhaust pushes rocket forward.
No need for air â this works even in space!
đž Example: Walking
When you walk:
Your foot pushes backward on the ground.
The ground pushes you forward with equal force.
Thatâs why you move forward. If you walk on ice and your foot slips, you can't push the ground â you donât move well.
â ď¸ Important Points to Remember
Forces always come in pairs â you can never have just one.
They act on different objects. Thatâs why they donât cancel each other out.
Example:
Gun pushes bullet forward.
Bullet pushes gun backward (recoil).Bullet flies, gun recoils â forces are equal but on different bodies.
The reaction force is not a response after time â itâs simultaneous.
đŹ Where it becomes very deep
This law connects to conservation of momentum.Because both forces are equal and opposite, their momenta also cancel out â total momentum of the system stays constant. This is why:
Rockets work
Collisions obey rules
Atoms push on each other correctly
Planets orbit properly
Even in quantum physics, particles "feel" each other through equal and opposite forces.
âď¸ Deeper idea: Field Interactions
Forces come from fields â like electric and magnetic fields. Even in these invisible interactions:
Two charges exert equal and opposite electric forces.
Two magnets exert equal and opposite magnetic forces.
Even in gravity, Earth pulls you down, but you also pull Earth up (tiny effect).
đĽ Misconceptions to Avoid
â People think:
Action causes reaction later â Wrong
They cancel out â Wrong, because they act on different objects.
âď¸ Always think in terms of force pairs:
If you feel a force, itâs because something is pushing back on you.
𧪠Summary in Deep Scientific Terms:
Newtonâs third law expresses the symmetry of forces in interactions.
It reflects the conservation of momentum and the fact that all forces are mutual interactions.
There are no isolated forces in nature â all forces come in pairs, ensuring balance and predictability in physical systems.
had posted about this
How a Research Student Should Approach This Topic
As a young researcher, you should not just accept the law. You should question it, test it, and connect it to the world around you.
Start with Observation: Look for examples of the third law everywhere. Don't just think about the examples given. Find your own in sports, in the kitchen, or even by just sitting in your chair.
Connect to Other Ideas: How does this law connect to energy? How does it connect to other laws of motion? Science is not a set of separate facts; it's a connected web of ideas.
Find the Limits: Does this law work for everything? Does it work for light? Does it work for things that are very, very small, like atoms? Researching the limits of a law is a key part of science.
3 Questions to Make You Think Deeper
Here are three questions designed to make you think more deeply about Newton's Third Law:
When a car crashes into a small insect, the force on the car and the force on the insect are equal. Why is the result so different for the car and the insect?
Imagine you are floating in space far from any planet and you have a heavy rock. How could you use Newton's Third Law and the rock to move yourself?
5 Key Points to Explore More
To go deeper into this topic, you should explore these five areas:
Conservation of Momentum: This is the most important idea connected to the third law. Research how the "equal and opposite" forces guarantee that the total momentum of a system never changes.
Force Pairs in Different Situations: Investigate how action-reaction pairs work with non-contact forces like gravity and magnetism. How do two magnets push each other apart without touching?
The Role of Mass: Explore Newton's Second Law (Force = mass Ă acceleration) and see how it works with the Third Law. This will help you answer the questions about the apple and the car crash.
Structural Engineering: Look into how engineers use Newton's Third Law to design buildings, bridges, and arches that can stand up to massive forces without collapsing.
Beyond Newton: Briefly look at how these ideas work in Einstein's theory of relativity or in quantum mechanics. Do forces always have to be equal and opposite in those advanced theories?