Newton’s 3rd Law of Motion: Definition, Examples & Equation
Newton’s 3rd law of motion states that action and reaction are always equal but opposite in direction. Common examples of newton’s third law of motion are: A horse pulls a cart, a person walks on the ground, a hammer pushes a nail, magnets attract paper clip. In all these examples a force exerted on one object and that force is exerted by another object.
Newton’s third law of motion explains quantitatively how forces affect motion. But question is that where these forces come from? We noticed during observations that a force on any object always exerted by another object.
But Isaac newton realized that things are not one-sided. It is true because, in the example of hammer and nail, the hammer exerts a force on the nail, but the nail exerts a force back on the hammer as well, due to this the speed of the hammer rapidly reduced to zero.
Only a strong force can reduce the speed of the hammer, thus newton said that the two objects must be treated on an equal base, such as the hammer exerts a force on the nail and the nail exerts a force back on the hammer. This is the cause or essence of newton’s 3rd law of motion.
See Also: Newton’s first law of motion examples
Newton’s Third law of motion definition
Newton’s 3rd law of motion deals with the reaction of a body when a force acts on it. Let body A exerts a force on another body B, body B reacts against this force and exerts a force on body A. The force exerted by body A on B is the action force whereas the force exerted by body B on A is called the reaction force. Newton’s 3rd law of motion states that:
“To every action, there is always an equal but opposite reaction.”
According to this law, the action is always accompanied by a reaction force and the two forces must always be equal and opposite. Note that action and reaction forces act on different bodies.
Newton’s 3rd law of motion tells us four characteristics of forces.
- Forces always occur in pairs (action and reaction forces).
- Action and reaction are equal in magnitude.
- Action and reaction are opposite in direction.
- Action and reaction act on different bodies.
Examples of law of action and reaction
- A book lying on a table
The weight of the books is acting on the table in a downward direction. This is the action, The reaction of the table acts on the books in the upward direction.
- The motion of the air-filled balloon
Take an air-filled balloon is set free, the air inside it rushes out and the balloon moves forward. In this example, the action is by the balloon that pushes the air out of it when set free. The reaction of the air which escapes out from the balloon acts on the balloon forward. A rocket moves on the same principle. When its fuel burns, hot gases escape out from its tail at very high speed. The reaction of these gases on the rocket causes it to move opposite to the gases rushing out of its tail.
What is some Examples of Newton’s third law of motion Everyday life?
Next, a list of situations in everyday life will be presented in which what is posed by Newton’s third law is reflected :
- If you have ever jumped from a raft into the water, you will have seen it fall back as your body moves forward. This is an example of Newton’s third law since there is action, which is his jump, and reaction, which is the recoil of the raft.
- Newton’s third law can be seen for example when we try to push someone into a pool. What will happen to us, even without the intention of the other, we will go backward?
- While swimming in a pool you can also experience Newton’s third law. This occurs when we look for a wall and push ourselves to gain momentum. In this case, an action and a reaction are also detected.
- The carpenters constantly find themselves before a clear example of Newton’s third law, when they hammer a nail. While the latter goes deeper and deeper into the wood when hammered, the hammer makes a backward movement, which is identified as the reaction of its own blow.
- The action and reaction identified in Newton’s third law can be observed when an individual pushes another who has a similar body. In this case, not only the pushed person will go back, but also the one who pushed him.
- The clothesline where clothes are hung is another example of Newton’s third law. While the clothes force down, the rope, in reaction, forces up. This ensures that the clothing does not come into contact with the ground.
- Rowing in a boat also means putting Newton’s third law into practice and this happens because while we move the water backward with the paddle, it reacts by pushing the boat in its opposite direction.
- When two people pull the opposite senses of the same rope, and it stays at the same point, it is also observed that there is an action and a reaction. That is why the game of the rope or the “push and pull” is perfectly suited as an example of this law.
- The third law can also be clearly observed when a person tries to push a stuck car. While it exerts force in one direction, the car reacts by exerting an equivalent, but in the opposite direction.
- A walk can also be a way to put Newton’s third law into practice. And this happens when we walk, for example, on the beach: while with our feet we exert force forward with each step, we push the sand backward.
- The operation of an airplane also works as a clear example of Newton’s third law since it advances forward as a consequence of the turbines forcing the opposite side, that is, backward.
- A rocket also manages to be put into operation thanks to Newton’s third law since it moves thanks to the effect of burnt gunpowder, which goes in the opposite direction.
Newton’s 3rd law of motion also known as action and reaction law.
We learn about the law of action and reaction.
Law of action and reaction
The principle of action and reaction is the third of the laws of motion formulated by Isaac Newton and one of the fundamental principles of modern physical understanding. This principle says that everybody A that exerts a force on a body B, experiences a reaction of equal intensity but in the opposite direction. The original formulation of the English scientist was as follows:
“With every action, there is always an equal and opposite reaction: it means that the mutual actions of two bodies are always the same and directed in the opposite direction .”
The classic example to illustrate this principle is that when we push a wall, we apply a certain amount of force to it, and it applies an equal amount to us but in the opposite direction. This means that all forces manifest in opposite pairs.
The original formulation of this law left out some aspects now known for theoretical physics and did not apply to electromagnetic fields, but along with the other two previous ones (The Fundamental Law of Dynamics and the Law of Inertia ), he proposed the elementary principles of modern physics.
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Law of Action and Reaction examples
- Jump. When we jump we exert a certain force on the ground with our legs, which does not alter it at all due to its enormous mass. The reaction force, on the other hand, lifts us up into the air.
- Paddle. The oars are moved by a man in a boat and push the water with an amount of force that he prints on them; the water reacts by pushing the can in the opposite direction, which results in the advance on the surface of the liquid.
- Shoot. The force that the explosion of gunpowder exerts on the projectile, and that makes it shoot forward, prints on the weapon an equal load of a force known in the field of weapons as “recoil”.
- Walk. Each step is taken consists of a push that we give to the ground backward, whose response pushes us forward and that is why we move forward.
- A push. If one person pushes another of the same weight, both will feel the force acting on their bodies, sending them both back some distance.
- The rocket propulsion. The chemical reaction that takes place inside the first phases of space rockets is so violent and explosive that it generates an impulse against the ground whose reaction lifts the rocket up into the air and, sustained in time, takes it out of the atmosphere into space.
- The Earth and the Moon. Our planet and its natural satellite attract each other with a force of the same amount but in the opposite direction: Earth’s attraction on the Moon keeps it in orbit, and its reaction generates the phenomenon of the tides.
- Hold an object. When taking something in the hand, the gravitational attraction exerts a force on our limb, and this a similar reaction but in the opposite direction, which keeps the object in the air.
- Bounce a ball. The balls of elastic materials bounce when thrown against a wall because the latter gives them a similar reaction but in the opposite direction to the initial force with which we threw them.
- Deflate a balloon. When we allow the gases contained in a balloon to escape, they exert a force whose reaction on the balloon pushes it forward, with a speed equal to that which the gases reach their exit.
- Pulling on an object. When we pull an object we print a constant force that generates a proportional reaction on our hands, but in the opposite direction.
- Hitting a table. A punch to a surface, like a table, prints on it a quantity of force that is returned, in reaction, by the table directly to the fist and in the opposite direction.
- Climb a crack. When climbing a mountain, for example, mountaineers exert a certain force on the walls of a crack, which is returned by the mountain allowing them to stay in place and not fall into the void.
- Climb a ladder. The foot is placed on a step and pushes down, making the step exert an equal reaction but in the opposite direction and raise the body to the next and so on.
- Descend a boat. When we go from a boat to the mainland (a pier, for example), we will notice that when we exert an amount of force on the boat’s edge that propels us forward, the boat will move proportionally away from the dock as a reaction.
- Hitting a baseball. We print an amount of force against the ball with the bat, which in reaction prints the same force on the wood. This is why the bats can break while the balls are thrown.
- Hammer a nail. The hammer’s metal head transmits the force of our arm to the nail, driving it more and more into the wood, but the latter also reacts by pushing the hammer in the opposite direction.
- Propel yourself from a wall. Being in the water or in the air, when taking momentum from a wall what we do is exert on it a certain force, whose reaction will push us in the opposite direction directly.
- Hang clothes on the rope. The reason that freshly laundered laundry does not touch the ground is that the string exerts a reaction proportional to the weight of the laundry but in the opposite direction.
- Sit on a chair. The body exerts a force with its weight on the chair and it responds with an identical but in the opposite direction, keeping us at rest.
See Also: Newton’s second law of motion
- Flight of rocket
When the fuel of the rocket is burnt, hot gases rush out with great speed from the tail of the rocket. Due to the reaction of these gases rockets move forward in the upward direction.
Newton’s 3rd law (video)
- Newton’s first law of motion examples
- Newton’s second law of motion examples
- Newton three laws of motion
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very informative and very good way of explanation of examples….
Thank you i am really enlighten
thank you so much
very informative and innovative examples
You’ve got a mistake on this page. In the first image, it shows the action-reaction pairs as book-on-earth and table-on-book. This is not correct. The action-reaction pair for the gravitational attraction of the earth on the book is actually the gravitational attraction of the book on the earth. Action-reaction pairs are always the same type of force (friction, gravity, etc) and always act on different objects. In many cases the normal force is equal to the force of gravity as you showed, but not always. What if the table was in an elevator that was accelerating upwards? Then those forces would not be equal. Pairs of forces in the third law are always and fundamentally equal. You have just shown two forces that happen to be equal in this case.
Wow you are very smart there LB!