What is Reaction force: Definition and 111 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. J

    What is the magnitude of the Reaction Force?

    Homework Statement In my homework we are asked to find the magnitude of the reaction force at the pivot at a instant and earlier in the problem we found the magnitude of the angular speed at one instant, the magnitude of the angular acceleration at the same instant, and the magnitude of the...
  2. P

    Does the force of gravity ever have a reaction force?

    for example, a book is at rest on a table. One might say that the normal force is the reaction force. BUt reaction forces always have to be equal in magnitude, and you put an object on the book, then the normal force would increase to keep the book at rest, therefore the normal force is...
  3. T

    Equilibrium normal reaction force problem

    Homework Statement http://tunerspec.ca/school/question3.gif The Attempt at a Solution This should be easy, but I'm tired and just can't do it. If anyone can point me in the right direction that'd be great. I tried making a FBD, and had the equations: Tsin30^{\circ} - 752N = 0 344N -...
  4. U

    Unsolved Mystery: Accelerating Charges & Radiation Reaction Force

    It is often stated that ANY accelerating charge radiates, so this includes uniformly accelerating charges. But the radiation reaction force is proportional to the THIRD derivative of x, so it vanishes when acceleration is constant. What's the deal here? Here's a graph which supposedly shows...
  5. B

    Solve Homework: Find Acceleration & Reaction Force of Wedge

    Homework Statement A wedge of mass 4kg and angle 30 degrees is at rest on a smooth horizontal table. a mass of 1kg is placed on the smooth inclined face of the wedge and a horizontal force of 10N is applied to towards the vertical face of the wedge. Show that the acceleration of the wedge is...
  6. B

    Toy Airplane Flying: Lift Force vs. Reaction Force

    Hi I've got a question concerning a previous question I've done. A person is holding a toy airplane which flys in the air with a constant radius. is the lift force the same as reaction force? is it equal to the vertical component of the centripetal force and weight force of the airplane?
  7. F

    What Are the Reaction Forces When a Book is Pulled Upward by a String?

    The problem involves drawing a free-body diagram: A book lies on a flat table. It is given that the weight of the book is 20N. I assume that since the book is not moving, the Fn (normal force) should also be 20N. The next part of the problem states that a string tied to the middle of the book...
  8. Y

    Reaction force on a book resting on top of a table.

    Question: A book is resting on top of a table. 1. Do the downward force of gravity and the upward force of normal force constitute a 3rd law pair? (Yes/No) 2. The reaction to the force of gravity is exerted on the (earth/table/book) by the (earth/table/book). Its direction is...
  9. M

    Radiation Reaction Force (or Self Force of charge particle)

    Is it true that there are cases in which the radiation reaction force on an electron is nonzero even if its acceleration is constant? I am confused because the radiation reaction force is proportional to the time derivative of the acceleration. Also when considering the radiation reaction...
  10. B

    Looking at reaction force on a molecular level?

    Can anyone explain how a reaction force (for example the electrostatc force of the Earth on the stone, and the force of the stone on the earth) works on a molecular level? what is actually happening to *repel (if it does indeed repel??) the object
  11. F

    Is Earth's gravitational pull equal to an object's falling force?

    if an object is falling to earth, is the equal and opposite force to gravity (Newtons 3rd law) the pull of the Earth towards the object?
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