# Frame of reference and Pseudo forces

In summary, a frame of reference is a system used to describe the position and motion of objects, while an inertial frame of reference is one in which Newton's first law holds true. Pseudo forces, also known as fictitious forces, only appear in non-inertial frames and are used to explain the motion of objects in these frames. Some examples of pseudo forces include the centrifugal force, Coriolis force, and fictitious gravitational force.
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 to move backwards from his point of view?
its not pseudo force because the frame of reference is inertial.
the car accelerates and so does tge bob. But why in opposite direction?

Also if you have a person inside the car, since bob is at rest, he introducea the concept of psuedo force to balance tension and weight. Am I right?
How do you explain first case?

What causes the bob to move backwards from his point of view?
From the inertial observer's viewpoint, the bob is not moving backwards but is being dragged forwards by the tension of the bob. Since it is accelerating, you can deduce the angle that the pendulum makes.

You're wrong. For someone outside the car(who knows the car is accelerated), the bob is just trying to stay at rest, but the string pulls it along with the car. So to avoid the complication caused by the string, let's just say there is a big glass container that can move with non-zero acceleration. We also assume that there is mass inside this container that has no friction with the ground. Then if the container accelerates, the mass just remains at rest and people outside the container, just say container is accelerated and the mass is at rest. But people inside the container(who don't know the container is moving) see that the mass is moving with some acceleration. So they say there is a force acting on it.

The bob does not move backwards from the outside point of view. The car moves forward.
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 to move backwards from his point of view?
its not pseudo force because the frame of reference is inertial.
the car accelerates and so does tge bob. But why in opposite direction?
The car accelerates. The bob does not accelerate. At least not until the pendulum's angle has changed and tension increased, causing it to do so.

Also if you have a person inside the car, since bob is at rest, he introducea the concept of psuedo force to balance tension and weight.
For the person inside the car, tension and "weight" are not balanced. The weight includes a pseudo-force component that causes a net motion. The concept of the pseudo force is introduced so that Newton's second law is consistent with the observed motion.

Also if you have a person inside the car, since bob is at rest, he introducea the concept of psuedo force to balance tension and weight. Am I right?
Yes. From the non-inertial frame of the car, a pseudo force is introduced so that Newton's 2nd law can be used. Since the acceleration is zero (assuming it is in its final position, at an angle with the vertical), the net force, including the pseudo force, will be zero.

## 1. What is a frame of reference?

A frame of reference is a system of coordinates used to describe the position and motion of objects in space. It is an important concept in physics because it allows us to measure and understand the movement of objects relative to a specific point or observer.

## 2. What is an inertial frame of reference?

An inertial frame of reference is a frame of reference in which Newton's first law of motion, also known as the law of inertia, holds true. This means that an object at rest will remain at rest and an object in motion will continue to move at a constant velocity unless acted upon by an external force.

## 3. What is a pseudo force?

A pseudo force, also known as a fictitious force, is a perceived force that appears to act on an object in a non-inertial frame of reference. It is not a real force, but rather a mathematical construct used to explain the motion of objects in non-inertial frames, such as accelerating or rotating frames.

## 4. How are pseudo forces related to frame of reference?

Pseudo forces are directly related to frame of reference because they only appear in non-inertial frames. In an inertial frame, objects will follow the laws of motion without the need for additional forces. However, in a non-inertial frame, pseudo forces must be introduced to account for the apparent acceleration or rotation of objects.

## 5. What are some examples of pseudo forces?

Some common examples of pseudo forces include the centrifugal force experienced by objects in a rotating frame, the Coriolis force experienced by objects moving in a rotating reference frame, and the fictitious gravitational force experienced by objects in an accelerating frame, such as an elevator moving up or down.

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