# Free-falling vs Fermi-Walker

• emma83
In summary, free-falling refers to the state of an object under the sole influence of gravity, while Fermi-Walker describes the motion of an object in a curved space-time. The main difference is that Fermi-Walker takes into account the effects of both gravity and space-time curvature, while free-falling only considers gravity. Examples of free-falling include dropping a ball, while examples of Fermi-Walker include the motion of a satellite in orbit. Understanding these concepts is important for understanding the behavior of objects in the universe and developing theories of relativity.

#### emma83

What is the difference between a free-falling frame and a Fermi-Walker frame ?

Fermi-Walker is free-falling if the path is free-falling. But Fermi-Walker can also be constructed for an time-like worldline.

A free-falling frame and a Fermi-Walker frame are two different reference frames used in the study of general relativity. The main difference between the two is that a free-falling frame is an inertial frame, while a Fermi-Walker frame is a non-inertial frame.

In a free-falling frame, an object is in a state of free-fall due to the influence of gravity. This means that the object is not experiencing any external forces and is following a geodesic, or the shortest path in curved spacetime. In this frame, the laws of physics hold true and no additional forces are needed to explain the motion of objects.

On the other hand, a Fermi-Walker frame is a non-inertial frame that takes into account the effects of gravity and rotation. In this frame, objects do experience external forces due to the curvature of spacetime caused by the presence of massive objects. These forces are known as fictitious forces and are needed to accurately describe the motion of objects in a non-inertial frame.

In summary, the main difference between a free-falling frame and a Fermi-Walker frame is the presence of external forces. In a free-falling frame, no external forces are present, while in a Fermi-Walker frame, fictitious forces are needed to account for the effects of gravity and rotation. Both frames have their own uses in the study of general relativity and can provide valuable insights into the behavior of objects in curved spacetime.

## What is free-falling?

Free-falling refers to the state of an object when it is only under the influence of gravity. This means that there are no other external forces acting on the object, causing it to accelerate at a constant rate towards the ground.

## What is Fermi-Walker?

Fermi-Walker is a concept in general relativity that describes the motion of a free-falling object in a curved space-time. It takes into account the effects of both gravity and the curvature of space-time on the object's motion.

## What is the difference between free-falling and Fermi-Walker?

The main difference between free-falling and Fermi-Walker is that in free-falling, the object is only under the influence of gravity, while in Fermi-Walker, the object is affected by both gravity and the curvature of space-time. This means that a free-falling object will follow a straight path towards the ground, whereas a Fermi-Walker object will follow a curved path due to the effects of space-time curvature.

## What are some real-life examples of free-falling and Fermi-Walker?

An example of free-falling is dropping a ball from a height, where the only force acting on the ball is gravity. An example of Fermi-Walker is the motion of a satellite in orbit around a planet, where the satellite is affected by both gravity and the curvature of space-time caused by the planet's mass.

## How does understanding free-falling and Fermi-Walker contribute to our understanding of the universe?

Understanding free-falling and Fermi-Walker helps us to better understand the effects of gravity and space-time curvature on the motion of objects in the universe. It also plays a crucial role in developing theories of relativity and understanding the behavior of celestial bodies, such as planets and stars, in space.