What is Action and reaction: Definition and 24 Discussions

As described by the third of Newton's laws of motion of classical mechanics, all forces occur in pairs such that if one object exerts a force on another object, then the second object exerts an equal and opposite reaction force on the first. The third law is also more generally stated as: "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." The attribution of which of the two forces is the action and which is the reaction is arbitrary. Either of the two can be considered the action, while the other is its associated reaction.

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  1. G

    B General Relativity: Action & Reaction in Gravitation

    Hi, In general relativity, gravitation is not anymore a Force but a deformation of space time. I would like to know what's becomes the 3 law of Newton for gravity that action equal reaction ? When a apple fall on the earth, does "the force" is exactly the same as the one applied on Earth ...
  2. J

    I Does direct interparticle action imply advanced inertial forces?

    In his Nobel lecture (https://www.nobelprize.org/prizes/physics/1965/feynman/lecture/) Richard Feynman states that by varying the Schwarzschild-Tetrode-Fokker direct interparticle action $$A=-\sum_i m_i\int\big(\mathbf{\dot X_i}\cdot\mathbf{\dot X_i}\big)^{1/2}d\alpha_i+\frac{1}{2}\sum_{i\ne...
  3. ephphatha16

    Find Value of tan φ of Reaction Force | Isaac Physics

    1. Find the value of tan φ to 2 sf where φ is angle made by line of action of reaction force at hinge above horizontal. https://isaacphysics.org/questions/trapdoor_num Part B Angle of reaction forceHomework Equations Mass of uniform trapdoor: m=4.0kgm=4.0kgThe trapdoor is held open making an...
  4. R

    Elastic collisions and Newton's third law

    Hi everyone, I am new to this forum, and I'm having a hard time understanding Newton's third law and collisions, first of all I want to say that it is not homework and that I do know the basics of physics, vectors, energy, work, and momentum I also know and understand Newton's first and second...
  5. Javier Mont

    About moving through the air and Newton´s 3rd law

    How are we able to move trough the aire if the air exerts a force equal to the friction we use to push us through air? I´ve had this problem in my mind since some days now. I did this picture: url: https://www.kn3.net/60DAC45480AJPG.html
  6. Clara Chung

    B Action and reaction of a rocket in space.

    By conversation of momentum, the rocket can be propelled forward by ejecting mass like gas. However, how is the propelling force explained in terms of action and reaction? If gas is ejected, what does the force act on?
  7. Nantes

    Action and reaction when pushing an extremely long stick

    There is a classical thought experiment on trying to exceed the speed of light: if you push a light-year-long rod, on whose end is a button that will be pressed by the rod, wouldn't you be vastly exceeding the speed of light (which is the speed of cause & effect) by pressing the button...
  8. J

    Action and reaction when fast object is pushed

    Let's say Bob floats in space. Bob's identical twin Joe moves past Bob at relativistic speed. As Joe is passing by, Bob gives him more speed by pushing him with his hand. Somehow I just happen to know that Joe will feel a smaller force pushing him than what Bob feels. So my question is: Why is...
  9. Deepak K Kapur

    A question regarding action and reaction

    I hit a bench with my fist, I experience equal and opposite reaction... Science says, it is because the nuclei of the atoms of my fist come close to the nuclei of atoms of the bench and experience repulsion. Am I on the right track?...Are there other explanations?
  10. T

    Action and reaction are equal and opposite,but why dont they cancell ?

    Action and reaction are equal and opposite,but why don't they cancell ?... Unlike other forces, like for example.. it a body is pressed from top and below with a same force.. the body stays there and its said that the forces cancell out.. why not here ?
  11. N

    Action & Reaction: Equal Opposites

    Action and reaction are equal and opposite. So, when mass (matter) acts on space and bends it, why doesn’t space react to this action in any detectable way?
  12. T

    Action and Reaction or Conservation of Momentum?

    Basically, when a natural frequency acts on coke bottle, It resonates. During the resonance, the lump of air in neck of it goes under simple harmonic motion. It goes in and out the bottle, increasing and decreasing pressure of cavity of coke periodically. When air goes inside the bottle, the...
  13. K

    Action and reaction pair for buoyant force.

    According to Newton 3rd law, every action will have a reaction. but how about buoyant force? if the buoyant force is the force of water on object then the reaction force will be the force of object on water. but is it other name for this force? thanks for reply.
  14. N

    Newton's 3rd law: action and reaction

    I thought I understood it cause I always had the right answer ever since I learned about it. But now my friend asked me a question about why does a piece of chalk break if you put a heavy thing on it, say a car. If we just think about action and reaction, the forces have to be along a...
  15. A

    Do Multiple Reaction Forces Create Infinite Chains in Newton's Third Law?

    I have a 2 questions regarding Newton’s third law and I will explain them using examples: 1. Body A is pushing against Body B with a force F(AB), Now body B will push against body A with a reaction force F(BA) equal but opposite to F(AB). Now shouldn’t be another reaction force F2(AB) due to...
  16. Y

    Work done by action and reaction

    It is said in the test book that in general, when one body does negative work on a second body, the second body does an equal amount of positive work on the first body. However, when consider two magnets repelling each other and there is also a normal force acted on one of magnets by a wall...
  17. apeiron

    Newton's Third Law of Motion: Action & Reaction Impact on Creation

    Newton's third law of motion says that for every action there is an equal and opposite reaction. So how does that strong physical principle impact on philosophical questions like the creation of the universe (either by a prime mover like a god, or as some kind of QM fluctuation like the big...
  18. F

    Action & Reaction: Point & Extended Body

    In a generic case of a mass point and an extended body to interact with gravitational force, the total force on the point admits a reaction to be construed as, on the extended body ? The total force on the extended body do not arise from the interaction between two points, but between a...
  19. M

    Gravitational force: action and reaction

    Consider two particles 1 and 2 that can interact with each other but are isolated from their surroundings. If an internal force from particle 1, for example, a gravitational force, acts on particle 2, then there must be a second internal force—equal in magnitude but opposite in...
  20. T

    Is action and reaction instantanious?

    I know very little about physics, so I hope this is a pretty easy question. Action is always acting and reaction is always equal. Is this action and reaction instantanious, and if not, why not? I read around quite a bit but this alludes me. I hope my query is worthy of consideration. I...
  21. T

    Action and Reaction - I. Newton

    Hi, I have for me a complex question! :( If I get to Mt. Everest (let's say - highest place on Earth), then there is acceleration of my body towards the Earth - because of g - gravity force. Now - question is does Earth have acceleration towards my body - as 3rd Isaac N. law would say...
  22. M

    Forces, action and reaction pairs

    Homework Statement A high diver of mass 83.0 kg jumps off a board 10.0 m above the water. If his downward motion is stopped 1.90 s after he enters the water, what average upward force did the water exert on him? Homework Equations \sumForces = ma X=X_{0}+V_{i}+1/2at The Attempt...
  23. D

    Can I Learn to Understand Human Action and Reaction?

    Hello! Anybody know any good pieces of work that will allow me to learn how to judge and react to another persons action or reaction to a particular event? Like how most human minds work in case scenario's and such. eh? Arigato, Chocobo
  24. T

    Exploring Action and Reaction with Magnetic Coils

    This is probably off the wall but I would like some other peoples opinions none the less. Imagine two 10kg, 1 meter long pipes that are closed off at each end. At the ends are magnet coils to propel and object back and forth. Inside the pipes there is a magnet disk/ball/whatever that is 1kg...
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