# Questions tagged [reference-frames]

A reference frame is a particular coordinate system chosen to represent physical entities. The notion is most often used in special and general relativity to denote particular coordinates chosen on the spacetime manifold.

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### How does special relativity explain the exchange of things between two observers? [closed]

Consider two observers, O1 and O2, each in their own inertial reference frames, with their frames passing by each other. Each observer has an orange tree, and they exchange oranges as their frames ...
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### Does gravitational acceleration vary when changing Galilean reference frames in special/general relativity?

The Lorentz transformations allow us to deduce how the acceleration of a material body changes when we move from one Galilean reference frame to another. But what if we consider not the acceleration ...
1 vote
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### What is the physical meaning of Riemann normal Coordinates?

It's a beginner's question and hopefully not to trivial for this forum: The frame of Riemann normal coordinates (RNC) with regard to a point $P$ in a given metric $g$ is often said to be the reference ...
350 views

### Active and passive transformation

Some active transformations on the system can be seen also as passive transformations for example the rotation of the system can be seen as the rotation of the observer in the opposite direction. ...
1 vote
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### Wave hits beach-example: Does sweeping crest constitute a Frame of Reference?

A long wave rolls in at 1 m/s and hits an almost parallel beach. It's 900k km long, and hits the beach at .1 micro degrees. Basic math tells us the crest of the wave rides down the beach at a speed of ...
442 views

### Newton's first law and Inertial systems

Newton's first law is part definition and part experimental. Isolated bodies move uniformly in inertial systems by virtue of the definition of an inertial system. In contrast, the assertion that ...
1k views

### Coordinate transformations in general relativity

Let's assume a non-rotating point mass with mass $M$. A non-massive object travels with constant velocity $\mathbf{v}_t$, with respect to the point mass, in the vicinity of the point mass. A non-...
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### Using Newton's Second Law of Rotation [closed]

According to Newton's Second Law of Rotation $$\tau_O=I_O\alpha$$ for the torque $\tau_O$ about $O$, the rotational inertia $I_O$ about $O$, and the angular acceleration $\alpha$. I'm getting confused ...
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### Effect of a spring’s mass on acceleration in a mass-spring system

Suppose a mass $M$ is connected to a spring with a spring constant $k$ and mass $m$. Now, assume the system is subjected to a constant acceleration $a$, causing the spring to stretch by a constant ...
1 vote
560 views

### Why do internal torques cancel?

I don't understand why torques produced by internal forces cancel in the sum $\sum \tau$. My textbook gives the following explanation: due to N3L, if a particle exerts a force on another particle of ...
247 views

### Meaning of point of application

Work is done when an applied force displaces the point of application in the same direction as the force. I don't understand this definition. The point of application is defined as the point at which ...
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### Angular Acceleration of a rigid body about different axes

Angular acceleration of a rigid body about any axis is the same. Is this statement true? If yes, then why? If not, then what's the mistake in this? PS:I know there are similar questions already asked ...
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### Do hurricanes spin?

It is often said that the spin of a hurricane forms as a result of being in a rotating reference frame with the spin caused by the coriolis force. For example, if you’re on a merry-go-round and you ...
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### How the represetation of the motion of a projectile depends on the reference system? [closed]

The question is about the motion (no air drag) of a projectile
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### How the represetation of the motion of a projectile depends on the reference system? [closed]

The question is about the motion (no air drag) of a projectile
1 vote
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### Kinematics in moving reference frames

Assume we have an object moving along a path $p_W(t)$ that is described in some fixed reference frame $W$. If we now have a second reference frame $B$ which differs from $W$ by some time varying ...
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### Simulate the dynamics of a 3D discrete rigid body from "first principles"

The question stems from wanting to implement a rigid body dynamics simulation without resorting to any of the well-known concepts that are commonly used, such as moment of inertia, torque, and angular ...
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### What is wrong with my relativistic explanation of the bucket argument by Newton? [closed]

Newton's bucket argument in my view: Time dilation is greater at the outer edge of the rotating bucket according to special relativity. This is analogous to gravity in the classical limit. As a result,...