What is Pseudo force: Definition and 17 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.

View More On Wikipedia.org
  1. burian

    How to solve questions in pseudo force frames?

    $$ \frac{62 - .4mg + (.2) (m_{net} g)}{m} = a(t)$$ And, then I put ths into $$S=\frac{1}{2} at^2$$ But, my answer is not quite coming with what's in the options? So, my main confusions are, SHould the bottom most surface exert a force on the top most block, also where am I making mistakes...
  2. S

    Mechanics Question -- The direction of the pseudo force

    I'm often got confused about why the direction of pseudo force is taken opposite to the direction of motion of the body. As specific, I have this question. In this, I didn't understood about why the direction of pseudo force is taken in right, in the diagram of solution provided to this...
  3. Like Tony Stark

    Understanding Pseudo-Forces in Non-Inertial Frames

    I know that, if my ##X## axis is aligned with the arm, there is friction pointing to ##O## and the ##x## component of the weight. Then, on the ##Y## axis, there is the normal force and the ##y## component of the weight. Supposing that I am situated on the arm (non inertial frame), where is the...
  4. Prabs3257

    Laws of motion and a projectile thrown from an accelerating elevator car

    At the moment of throwing the ball the ball will have a vertical vel of 4 and horizontal of 3 wrt to elevator so as seen from inside the elevator the ball will behave like a projectile where g(eff) = 8 and with time period 1 sec hence range will be the displacement which should be 3 m but ans...
  5. Abhishek11235

    I Doubt in the Application of a Pseudo Force

    Here is the problem in Morin. In this problem he takes the person on carousel as origin. Accordingly,when he begins to apply Newton's Law of motion on himself,by the equation of pseudo force,since he is motionless in his own frame,his own acceleration is 0. Further in his own frame he has 0...
  6. C

    Body Force vs Inertial Force: What's the Difference?

    Hello everyone. This is my first time on the physics forum, but I think I'm going to be a regular here. I was reading a paper that outlined various ways to approach solving dynamic problems. The first approach outlined by the author is D'Alembert's principle of virtual work. In describing...
  7. T

    How to avoid the use of a pseudo force

    Homework Statement [/B] Homework Equations f = ma The Attempt at a Solution t1 tension in string connecting Mc t1 tension in string connecting Ma and Mb ## m_c:\\ m_c g - T_1 = m_c a_c\\ ## i considered pseudo for acting on masses b and a from a non inertial frame of reference hence in that...
  8. EastWindBreaks

    Normal force in a curvilnear motion

    Homework Statement The system shown is initially at rest when the bent bar starts to rotate about the vertical axis AB with constant angular acceleration a 0 = 3 rad/ s2 . The coefficient of static friction between the collar of mass m = 2 kg and the bent bar is f.Ls = 0.35, and the collar is...
  9. C

    Container of Liquid Accelerated Upward

    Homework Statement A block floats partially submerged in a container of liquid. When the entire container is accelerated upward, which of the following happens? Assume that both the liquid and the block are incompressible. A) The block descends down lower into the liquid. B) The block does...
  10. Titan97

    Newton's law problem on homogeneous flexible rope

    Homework Statement A homogeneous flexible rope rests on a wedge whose sides make angles α and β with horizontal. The centre of rope lies on C. With what acceleration should the wedge be moved for the rope to stay stationary with respect to wedge? (all surfaces are smooth). Homework Equations...
  11. AdityaDev

    Frame of reference and Pseudo forces

    If you have a car and a pendulum is hanged inside it, and if you watch from outside the car,and if the car has some acceleration, then you see the bob moving in opposite direction of motion of car. For a person standing outside, he knows that the car has some acceleration. What causes the bob...
  12. binbagsss

    Pseudo Force Direction Confusion.

    Q1) What angular velocity would be required for your effective weight at the equator to be third of that the north pole? You may neglect all inertial forces except the centrifugal. I understnad the majority of my books solution which is that: At the equator, the centrifugal force is...
  13. A

    What Is the Minimum Acceleration for a Mass to Fall Freely on a Wedge?

    Homework Statement a block of mass m is resting on a wedge of angle θ as shown in fig. the wedge is given an accn. a towards left.what is the minimum value of a due to an external agent for which the mass will fall freely? Homework Equations N+m(asinθ) = 0.(N is the normal force)...
  14. K

    What Are the Best Books to Understand Pseudo Forces in Physics?

    Can anyone tell me books for reading about the pseudo force?
  15. U

    Difference between pseudo force and centrifugal force

    what is pseudo force and centrifugal force? can anyone differentiate between them? is one a special case of the other?
  16. A

    Tension in a string along with a Pseudo force

    Homework Statement A block of mass 50g is suspended from the ceiling of an elevator.Find the tension in the string if the elevator goes up with an acceleration of 1.2m/s^2 Homework Equations F_{net}=ma_{net} The Attempt at a Solution I have reached here:...but with this i don't get the...
  17. D

    Is Earth's Gravitational Pull Just a Pseudo Force?

    I was reading about the Principle Of Equivalence as proposed by Einstein which proved that Inertial Mass and Gravitational Mass is one and the same thing. Further it proved that if we are in a spaceship and flying in space with acceleration 'g' upwards, the person is bound to the surface of the...