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Pseudo Force - Definition, Explanation, FAQs

Pseudo Force - Definition, Explanation, FAQs

Vishal kumarUpdated on 02 Jul 2025, 05:00 PM IST

The pseudo force, otherwise known as fictitious force, signifies an imaginary force coming into being when relating to non-inertial reference frames such as accelerating or rotating systems. The acceleration of the observer causes such pseudo forces and not any real interaction; appears to act opposite to the motion of the reference frame. It is well experienced when pushed back by a speeding car or thrown outward by a spinning merry-go-round.

Pseudo Force - Definition, Explanation, FAQs
Pseudo Force

What is Pseudo Force?

An apparent force or pseudo force generally works on all masses whose motion can be described by using a rotating reference frame or some other noninertial frame of reference. Thus, pseudo force defined as a frame of reference should simply accelerate relative to some non-accelerating frame. Rather than any kind of physical interaction between two objects, the force F is generated due to the acceleration 'a' of the non-inertial reference frame. As frames, pseudo forces can accelerate in any direction.

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Pseudo Force Formula

The mass and acceleration of an object determine the net force acting on it. In a similar vein, the pseudo-force formula is as follows:

$$
F_p=-m a
$$
Where,
$F_p=$ Pseudo force acting on an item.
$\mathrm{m}=$ mass of an object.
$a=$ acceleration of the frame of reference of an item.
A negative sign suggests that a pseudo force is acting in opposition to the frame of reference acceleration of an item.

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Examples

A straight line of Speed

Every time a car accelerates quickly, it is natural to feel "pushed back into the seat." In an inertial frame of reference with respect to the road, there is no pull on the driver in the backward direction. The acceleration of the car creates a frictional force pushing the backwards in the non-inertial reference frame of the driver.

Elevator Scenario

Let us consider a scenario where a person having mass m is standing on a weighing machine that is placed in a stationary elevator. The actual weight of a person is mg. The weighing machine offers a normal reaction N, the weight ' mg ' is a reading of this machine. The motion of the elevator decides the weight of the man.

Difference Between Pseudo Force and Real Force

Pseudo ForceReal Force
A pseudo force is one that develops as a result of the observer's frame of reference speeding up.

Real force is defined as a force that is created as a result of an interaction between objects.

Newton's law of motion is not followed by pseudo force.

Newton's law of motion is observed by real force.

Force felt when a car suddenly accelerates (backward push), centrifugal force in a rotating frame

Gravitational force, tension in a rope, friction, normal force.

Frequently Asked Questions (FAQs)

Q: What is the pseudo force experienced by a person in an elevator that suddenly stops?
A:
When an elevator suddenly stops, a person inside experiences an upward pseudo force. This force is equal to the person's mass multiplied by the elevator's deceleration. It creates a momentary sensation of being pushed upward or feeling lighter, which is opposite to the feeling when the elevator starts moving upward.
Q: How do pseudo forces affect the shape of water's surface in a rotating container?
A:
In a rotating container, pseudo forces (mainly the centrifugal force) cause the surface of water to form a parabolic shape. The water climbs up the sides of the container, with the surface curving upward from the center. This shape results from the balance between the outward centrifugal force and the downward gravitational force.
Q: Can pseudo forces ever cancel each other out?
A:
Yes, pseudo forces can cancel each other out in certain situations. For example, in a rotating frame that's also accelerating linearly, the centrifugal force and the pseudo force due to linear acceleration could potentially cancel each other at certain points. However, this cancellation would generally only occur at specific locations or instants.
Q: How do pseudo forces affect the motion of objects dropped in a rotating frame?
A:
Objects dropped in a rotating frame experience pseudo forces that alter their apparent path. The Coriolis force causes the object to deflect sideways as it falls, while the centrifugal force causes it to fall "outward" relative to the rotation axis. The resulting path, as seen in the rotating frame, is a curve rather than a straight line.
Q: What is the pseudo force experienced by a person in a rotating space habitat?
A:
In a rotating space habitat, a person experiences a centrifugal pseudo force that mimics gravity. This force acts radially outward from the axis of rotation and its magnitude increases with distance from the axis. The rotation rate and radius are typically designed to produce a force equivalent to Earth's gravity on the habitat's outer rim.
Q: How do pseudo forces affect the apparent gravity on different parts of Earth?
A:
Pseudo forces, mainly the centrifugal force due to Earth's rotation, affect the apparent gravity at different locations on Earth. This force is strongest at the equator and zero at the poles, causing a slight reduction in apparent gravity at the equator. This effect, combined with Earth's equatorial bulge, results in about a 0.3% difference in surface gravity between the equator and poles.
Q: Can pseudo forces ever vary with position in a reference frame?
A:
Yes, pseudo forces can vary with position in a non-inertial reference frame. For example, in a rotating frame, the magnitude of the centrifugal force increases with distance from the axis of rotation. Similarly, the Coriolis force depends on the velocity of an object relative to the rotating frame, which can vary with position.
Q: How do pseudo forces affect the formation of planetary rings?
A:
Pseudo forces, particularly the centrifugal force, play a crucial role in the formation and maintenance of planetary rings. In the rotating frame of the planet, the outward centrifugal force balances the inward gravitational force, allowing ring particles to maintain stable orbits. This balance determines the structure and dynamics of the ring system.
Q: What is the pseudo force experienced in a car going around a banked curve?
A:
In a car going around a banked curve, passengers experience a combination of pseudo forces. The main one is the centrifugal force pushing outward from the center of the curve. There's also a component of the centrifugal force pushing down the bank due to the inclination. These forces combine with gravity to determine the apparent forces on the passengers.
Q: Can pseudo forces ever act perpendicular to the direction of acceleration?
A:
Yes, the Coriolis force, a type of pseudo force, acts perpendicular to both the velocity of an object and the axis of rotation of the reference frame. This perpendicular action is what causes the deflection of moving objects in rotating frames, such as the apparent deflection of winds and ocean currents on the rotating Earth.
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