What is Fictitious force: Definition and 22 Discussions

A fictitious force (also called a pseudo force, d'Alembert force, or inertial force) is a force that appears to act on a mass whose motion is described using a non-inertial frame of reference, such as an accelerating or rotating reference frame. An example is seen in a passenger vehicle that is accelerating in the forward direction – passengers perceive that they are acted upon by a force in the rearward direction pushing them back into their seats. An example in a rotating reference frame is the force that appears to push objects outwards towards the rim of a centrifuge. These apparent forces are examples of fictitious forces.
The fictitious force F is due to an object's inertia when the reference frame does not move inertially, and thus begins to accelerate relative to the free object. The fictitious force thus does not arise from any physical interaction between two objects, such as electromagnetism or contact forces, but rather from the acceleration a of the non-inertial reference frame itself, which from the viewpoint of the frame now appears to be an acceleration of the object instead, requiring a "force" to make this happen. As stated by Iro:
Such an additional force due to nonuniform relative motion of two reference frames is called a pseudo-force.
Assuming Newton's second law in the form F = ma, fictitious forces are always proportional to the mass m.
The fictitious force on an object arises as an imaginary influence, when the frame of reference used to describe the object's motion is accelerating compared to a non-accelerating frame. The fictitious force "explains," using Newton's mechanics, why an object does not follow Newton's laws and "floats freely" as if weightless. As a frame can accelerate in any arbitrary way, so can fictitious forces be as arbitrary (but only in direct response to the acceleration of the frame). However, four fictitious forces are defined for frames accelerated in commonly occurring ways: one caused by any relative acceleration of the origin in a straight line (rectilinear acceleration); two involving rotation: centrifugal force and Coriolis force; and a fourth, called the Euler force, caused by a variable rate of rotation, should that occur.
Gravitational force would also be a fictitious force based upon a field model in which particles distort spacetime due to their mass, such as general relativity.

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  1. Rikudo

    Fictitious force in a binary stars

    I have a difficulty in understanding the question. Fictitious force is a force whose motion is described using a non-inertial frame of reference. Which frame is the question referring to?
  2. D

    B Why Does a Body Experience Fictitious Force on Accelerating Objects?

    Why does a body experience a fictitious force when placed over an object which is accelerating ? I mean why it doesn't just accelerate with an object... What's actually happening?
  3. Livio Arshavin Leiva

    Rectilinear movement seen from a rotating reference frame

    Let's suppose there's some platform that is rotating with angular speed omega and has a radius R. At t=0 we release some object from the border, which has an initial speed perpendicular to the radius direction with magnitude \omega R and we want to know its position at t=T with respect to the...
  4. S

    Classical Book about center of mass frame of reference and fictitious force

    Hello I have learned about conservation of momentum, Newton's law (1st, 2nd, 3rd law + free body diagram), conservation of energy and finding center of mass of several 2 D and 3 D shapes (non - calculus method). I watched youtube video about two objects connected by horizontal spring and in...
  5. L

    Effective acceleration due to gravity in non-inertial frame

    Take some sort of system accelerating with respect to an inertial reference frame: let's take a spherical mass on the end of a string forming a simple pendulum with the ceiling of a car, and allow that car to accelerate uniformly. Could someone share with me how they interpret the concept of a...
  6. Soffie

    The period of oscillation of a bob in an accelerating frame

    If a suspended pendulum bob is accelerated (in a car, for example), if you're in the accelerating frame of reference, you will observe the fictitious force which appears to act on the bob (as you're in the accelerating frame, the bob is not 'moving' so to speak, so to establish equilibrium you...
  7. Clara Chung

    Linear fictitious force problem

    Homework Statement Homework EquationsThe Attempt at a Solution I understand the solution of the problem, but I want to know why don't my approach work. I didn't change the frame of reference. I use the regular method of solving a torque problem. (mgsinθ - mAcosθ)(L/2) = mL2/3 θ'' which is...
  8. F

    Coriolis effect example: ball tossing on rotating carousel

    Hi all, I was reviewing the Coriolis effect and I came across the attached explanatory image (from the Italian version of a book on physics by Cutnell, Johnson, Young and Stadler). The idea is the following. two guys are facing each other on a rotating carousel; one of the guys on the throws...
  9. J

    What causes the bending of this rod?

    In this video, a man applies an angular acceleration to the base of a rod. While the rod rotates, it bends. Why? What force is there that causes the bending, aside from rod's own weight? It seems to me to be the work of a fictitious inertial force. I was always taught that those forces don't...
  10. F

    Acceleration due to fictitious force independent of mass?

    I have been asked by someone if it is true that in general, for a constantly accelerating reference frame, i.e. a non-inertial reference frame, the acceleration of a particle (as observed in this frame) due to the corresponding fictitious force is independent of its mass. My response was yes...
  11. I

    I Unifying Gravity: The Quest to Understand a Fictitious Force

    If gravity is a fictitious force, why some scientists try to unify it with other real forces of nature?
  12. M

    Can all fundamental forces be fictitious force ?

    After reading many questions, , I wonder: is it possible to consider also the other fundamental forces, the electroweak interaction and the strong interaction or ultimately the unification of these, to be fictitious forces like gravity in the framework of general relativity? If we want a final...
  13. stripes

    What Forces Act on a Train Moving South in Edmonton?

    Homework Statement Depending on the college or university, this may be a 2nd or 3rd year question. For me, it is a junior-level course. A train is heading due south through Edmonton at a speed of 300 m/s relative to the surface. Edmonton has a latitude of 53.5 degrees; the Earth has a radius...
  14. N

    Interpretation of the fictitious force

    Hello. Before I ask a question I want you to remind that it is my first time to use this page. And I am not even good at speaking english. My question is about the fictitious forces. I have made a long proof for the formula of the force in the non-inertial reference frame with the second law of...
  15. TrickyDicky

    Does gravity as a fictitious force do work? (GR's free-falling frame POV)?

    This discussion started as a side clarification of something in this thread https://www.physicsforums.com/showthread.php?p=3971013#post3971013 and although tangentially related it probably deserves a thread of its own so anyone can participate without reservations. Please keep in mind I am not...
  16. R

    Is Gravity a Fictitious Force Only Valid in Quantum Physics?

    I'm really confused on this concept. Why is gravity considered a fictitious force and is it true that this concept is only valid in quantum physics? Thanks.
  17. e2m2a

    Is Centrifugal Force Real or Fictitious?

    It is standard pedagogy in our educational system to teach centrifugal force is a fictitious force, a force that arises within a non-inertial, rotating reference frame. High school students, for example, are brainwashed in believing this. Brainwashed because it perpetuates a false dogma about...
  18. putongren

    Understanding Fictitious Forces: A Mathematical Derivation

    I'm having trouble understanding fictitious forces, so I looked up the wiki for it http://en.wikipedia.org/wiki/Fictitious_force" . In the wiki entry, I have trouble understanding the mathematical derivation for fictitious forces in the early part of the article (along the mathematical...
  19. C

    Distinguish Fictitious Force: Real Vs. Acceleration

    can someone tell me how to distinguish fictitious and real force, together with the correlation of fictitious acceleartion and real acceleration, my research seems to fail on this subject
  20. B

    Fictitious Force: What Makes It Fictitious?

    [SOLVED] What is fictitious force? Hi. I was wondering if someone would be able to explain to me what is meant by fictitious force? I know that it is a force that acts on masses in a non-inertial frame of reference. That is to say, the motion of the car from the view of the driver, for...
  21. H

    Fictitious force and accelerating airplane

    [SOLVED] Fictitious force and accelerating airplane Homework Statement The question asks me to draw a free body diagram for a person standing in an accelerating airplane, and to indicate the fictitious force and any real forces acting on them. The airplane accelerates at 2.22 m/s^2...
  22. Antonio Lao

    Can Fictitious Force Become Real ?

    Can Fictitious Force Become Real ? Centrifugal force is considered as a fictitious force. For an object of m mass, it is given by F_{centrifugal} = - m \vec{a}_{centripetal} = \frac{mv^2}{r} \hat{r} The fictitiousness comes from the use of a noninertial rotating coordinate system for...