#### • Class 11 Physics Demo

Explore Related Concepts

#### • examples balanced unbalanced forces

From Wikipedia

Fictitious force

A fictitious force, also called a pseudo force, d'Alembert force or inertial force, is an apparent force that acts on all masses in a non-inertial frame of reference, such as a rotating reference frame.

The force F does not arise from any physical interaction but rather from the acceleration a of the non-inertial reference frame itself. As stated by Iro:

According to Newton's second law in the form F = ma, fictitious forces always are proportional to the mass m acted upon.

Four fictitious forces are defined in accelerated frames: one caused by any relative acceleration of the origin in a straight line (rectilinear acceleration), two caused by any rotation (centrifugal force and Coriolis force) and a fourth, called the Euler force, caused by a variable rate of rotation, should that occur.

## Background

The role of fictitious forces in Newtonian mechanics is described by Tonnelat:

## Fictitious forces on Earth

The surface of the Earth is a rotating reference frame. To solve classical mechanics problems exactly in an Earth-bound reference frame, three fictitious forces must be introduced, the Coriolis force, the centrifugal force (described below) and the Euler force. The Euler force is typically ignored because its magnitude is very small. Both of the other fictitious forces are weak compared to most typical forces in everyday life, but they can be detected under careful conditions. For example, LÃ©on Foucault was able to show the Coriolis force that results from the Earth's rotation using the Foucault pendulum. If the Earth were to rotate a thousand times faster (making each day only ~86 seconds long), people could easily get the impression that such fictitious forces are pulling on them, as on a spinning carousel.

## Detection of non-inertial reference frame

Observers inside a closed box that is moving with a constant velocity cannot detect their own motion; however, observers within an accelerating reference frame can detect that they are in a non-inertial reference frame from the fictitious forces that arise. For example, for straight-line acceleration:

Other accelerations also give rise to fictitious forces, as described mathematically below. The physical explanation of motions in an inertial frames is the simplest possible, requiring no fictitious forces: fictitious forces are zero, providing a means to distinguish inertial frames from others.

An example of the detection of a non-inertial, rotating reference frame is the precession of a Foucault pendulum. In the non-inertial frame of the Earth, the fictitious Coriolis force is necessary to explain observations. In an inertial frame outside the Earth, no such fictitious force is necessary.

## Examples of fictitious forces

### Acceleration in a straight line

Figure 1 (top) shows an accelerating car. When a car accelerates hard, the common human response is to feel "pushed back into the seat." In an inertial frame of reference attached to the road, there is no physical force moving the rider backward. However, in the rider's non-inertial reference frame attached to the accelerating car, there is a backward fictitious force. We mention two possible ways of analyzing the problem:

1. Figure 1, (center panel). From the viewpoint of an inertial reference frame with constant velocity matching the initial motion of the car, the car is accelerating. In order for the passenger to stay inside the car, a force must be exerted on the passenger. This force is exerted by the seat, which has started to move forward with the car and is compressed against the passenger until it transmits the full force to keep the passenger moving with the car. Thus, the passenger is accelerating in this frame due to the unbalanced force of the seat.
2. Figure 1, (bottom panel). From the point of view of the interior of the car, an accelerating reference frame, there is a fictitious force pushing the passenger backwards, with magnitude equal to the mass of the passenger times the acceleration of the car. This force pushes the passenger back into the seat, until the seat compresses and provides an equal and opposite force. Thereafter, the passenger is stationary in this frame, because the fictitious force and the (real) force of the seat are balanced.

How can the accelerating frame be discovered to be non-inertial? In the accelerating frame, everything appears to be subject to zero net force, and nothing moves. Nonetheless, compression of the seat is observed and is explained in the accelerating frame (and in an inertial frame) because the seat is subject to the force of acceleration from the car on one side, and the opposing force of reaction to acceleration by the passenger on the other. Identification of the accelerating frame as non-inertial cannot be based simply on the compression of the seat, which all observers can explain; rather it is based on the simplicity of the physical explanation for this compression.

The explanation of the seat compression in the accelerating frame requires not only the thrust from the axle of the car, but additional (fictitious) forces. In an inertial frame, only the thrust from the axle is necessary. Therefore, the inertial frame has a simpler physical explanation (not necessarily a simpler mathematical formulation, however), indicating the accelerating frame is a non-inertial frame of reference. In other words, in the inertial frame, fictitious forces are zero. See inertial frame for more detail.

This example illustrates how fictitious forces arise from switching from an inertial to a non-inertial reference frame. Calculations of physical quantities (compression of the seat, required force from the axle) made in any frame give the same ans

Lorentz force

In physics, the Lorentz force is theforce on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:

\mathbf{F} = q[\mathbf{E} + (\mathbf{v} \times \mathbf{B})],

where

F is the force (in newtons)
E is the electric field (in volts per metre)
B is the magnetic field (in teslas)
q is the electric charge of the particle (in coulombs)
v is the instantaneous velocity of the particle (in metres per second)
Ã— is the vector cross product

or equivalently the following equation in terms of the vector potential and scalar potential:

\mathbf{F} = q \left( - \nabla \phi - \frac { \partial \mathbf{A} } { \partial t } + \mathbf{v} \times (\nabla \times \mathbf{A})\right),

where:

A and Î¦ are the magnetic vector potential and electrostatic potential, respectively, which are related to E and B by
\mathbf{E} = - \nabla \phi - \frac { \partial \mathbf{A} } { \partial t }
\mathbf{B} = \nabla \times \mathbf{A}.

Note that these are vector equations: All the quantities written in boldface are vectors (in particular, F, E, v, B, A).

The Lorentz force law has a close relationship with Faraday's law of induction.

A positively charged particle will be accelerated in the same linear orientation as the E field, but will curve perpendicularly to both the instantaneous velocity vector v and the B field according to the right-hand rule (in detail, if the thumb of the right hand points along v and the index finger along B, then the middle finger points along F).

The term qE' is called the electric force, while the term qv' Ã—B is called the magnetic force. According to some definitions, the term "Lorentz force" refers specifically to the formula for the magnetic force:

\mathbf{F}_{mag} = q(\mathbf{v} \times \mathbf{B})

with the total electromagnetic force (including the electric force) given some other (nonstandard) name. This article will not follow this nomenclature: In what follows, the term "Lorentz force" will refer only to the expression for the total force.

The magnetic force component of the Lorentz force manifests itself as the force that acts on a current-carrying wire in a magnetic field. In that context, it is also called the Laplace force. The magnitude of this magnetic force is q v B sin Î¸ and direction is perpendicular to the plane formed by v and B. If the particle moves perpendicular to the field, the magnitude becomes q v B and the trajectory of the particle will be circular. Also the force is in the direction perpendicular to the velocity, so magnitude of velocity will not change, i.e. the motion will be uniform circular motion.

## History

Early attempts to quantitatively describe the electromagnetic force were made in the mid-18th century. It was proposed that the force on magnetic poles, by Johann Tobias Mayer and others in 1760, and electrically charged objects, by Henry Cavendish in 1762, obeyed an inverse-square law. However, in both cases the experimental proof was neither complete nor conclusive. It was not until 1784 when Charles-Augustin de Coulomb, using a torsion balance, was able to definitively show through experiment that this was true. Soon after the discovery in 1820 by H. C. Ã˜rsted that a magnetic needle is acted on by a voltaic current, AndrÃ©-Marie AmpÃ¨re that same year was able to devise through experimentation the formula for the angular dependence of the force between two current elements. In all these description, the force was always given in terms of the properties of the objects involved and the distances between them rather than in terms of electric and magnetic fields.

The modern concept of electric and magnetic fields first arose in the theories of Michael Faraday, particularly his idea of lines of force, later to be given full mathematical description by Lord Kelvin and James Clerk Maxwell. Interestingly Maxwell provided the equation for the Lorentz force in relation to electric cur

Question:On a science forces test, a question was 'if you hit a can of beans with a hammer, is it a balanced force or unbalanced force?' that was all the information they gave you. which one is it?

Answers:It is an unbalanced force...consider this definition of a balanced force... Two forces that are equal in size and opposite in direction. Balanced forces have a net force of zero. Two forces exert the same amount of force on an object, causing no change in motion. Two equal forces give off the same amount of force on an object. . When 2 objects are balanced there is no motion. So when you hit the can of beans with a hammer, there is nothing on the 'other side' of the can of beans to balance that force so it is considered an unbalanced force. I hope this helps.

Question:

Answers:Balanced swings left and balanced swings right

Question:uhh hey Goring..YOU ARE WRONG. my homework asks for examples which means i need to come up with some example for it. there are none that i can come up with and there are none in the book. so..keep the dumbness to yourself.

Answers:ummm... a balnaced force is something that is not moving maybe a textbook on a table. you can explain this because teh normal force of the table exerts on the books equals the force of gravity. an unbalanced force is something that is moving(not at constant speed) so maybe a rocket rising up into space. this can be explained because the force fo the upward thrust is larger than the force of the downward weight. i hope that i helped, if not write something back.

Question:Whats an example of a contact force, unbalanced force and a balanced force? 10 points go to the best answer.

Answers:Balanced: when you pick up a school book. The force of gravity downward on the book is equal to the force of your arm muscle pushing upward on the book. Unbalanced: when you skydive the force of gravity exceeds the force of friction from the air. Gravity force is greater which is why you fall toward the ground. Contact: simply the force when two objects are touching each exerting some form of force. Drawing a line is an example of contact force. The individual's pencil is in contact with the paper. The pencil is being pushed across the paper.