# 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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### Using time-dilation to our advantage?

Assume we have a super-computer working on an important problem, and we estimate it will take about $200$ years to solve. But, we need the answer in $20$ years. Could we ship the super-computer into ...
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### Understanding Mach Principle

I cannot get the essence of Mach's Principle. In my undestanding, it states that the cause of the so-called "fictitious forces" which arise in non-uniform motion has to be found in the relative ...
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### Does a magnet moving in a uniform electric field experience torque?

Assume a uniform electric field of $E_y$ along $y$ in the lab frame of reference $(x,y,z,t)$. A simple magnet bar is set in motion at $v$ along $x$ in this electric field so that the alignment of the ...
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### Inverted Pendulum on a Cart Problem and Moment of Inertia

In the classic inverted pendulum on a cart problem there is a pendulum represented with a point mass at a fixed distance from a horizontally free cart. A slight modification is to use a rod instead ...
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### Designating a coordinate system with multiple objects

So I am slightly new to physics, but am thoroughly enjoying the contextual thinking changes that physics brings about. My question is regarding coordinate system designation, on a group of individual ...
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### Pseudo force for the box on wedge

Can anyone please tell as im confused like why pseudo force acts on a block when we accelerate the wedge towards opposite direction, in my knowledge its coz of fram , which is wedge itself , but what ...
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### Weight in an elevator accelerating downwards with $2g$

I am aware of the classical apparent weight physics but I am confused about what happens when elevator falls with greater acceleration than g say two g or something.if I calculate the normal force it ...
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### Artificial Gravity - Practical Experiments [on hold]

I'm not a scientist but I am curious as to actual artificial gravity experiments conducted in a zero-gravity environment. I can't seem to find any but I've just read through some well thought out ...
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### Friction as a cause of motion

Can anyone help me to understand why friction force is not opposing the resultant centripetal force acting on the box and instead being the cause of its existence?
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### Reference frames symmetry in Special Relativity

I have a couple of questions related to reference frames in STR. Let's consider a rocket that is inertially moving towards a star with a relative velocity 0.9c. I'd like to look at this example ...
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### Blinking flashlight infalling into the black hole, as frequency → ∞

This is my third question from a series were I progressively refine my thought experiment. The others are: Can something (again) ever fall through the event horizon? Time of flashlight crossing the ...
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### What justifies the use of centre of mass?

Centre of mass gives the location where the 'weighted average' of all the elemental mass of a body acts. Considering that weighted average is one of the many statistical tools used to find the spread ...
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### Should all objects have equal acceleration to be considered a system?

Should all objects have equal acceleration to be considered a system?
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### Spacetime dilation Moon vs Earth [closed]

As I understand it, time will pass slightly faster on the surface of the moon compared to the earth This is due to the difference in velocity and gravitational fields of the two planets. How could I ...
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### Dependence of Compton effect on frame of reference

I want to know whether Compton effect depends on the frame of reference or not. The wavelength change is a thing, but does not depend on frame of reference since it depends only on $\theta$. But if I ...
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### Relationship between torque and force [duplicate]

While studying Newtonian mechanics, we are concerned with only three laws of motion that describes force and it's relations. But when we switch to rotational dynamics, we are presented with torque and ...
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### Equivalent fictitious forces on rigid body

I know that when I study the motion of a rigid body from a non-inertial frame, I have to take into account the fictitious forces. However, it is not straightforward to find the resultant force (and ...
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### How can this hinge point be at rest? [closed]

The given situation is shown in figure, my doubt is that point O must be accelerating but it is not possible. Where am I going wrong in my method? Please help
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### Transforming a tensor from Crystal to Laboratory frame of Reference

I want to transform the stiffness tensor of a rhombohedral crystal from crystallographic frame of reference to laboratory fame of reference, how to do it ? For crystal structures having orthogonal ...
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### Finding Direction of Angular Velocity

Suppose I have a 3D rigid object on which some external forces act at various points located on it. The resulting motion would, in general, be the translation of center of mass plus rotation about the ...
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### Acceleration in general relativity

Let's say that, from my point of view, another observer is accelerating. Now, from his point of view, he is standing still: all he feels is an overall fictitious force of gravity, which is just a ...
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### Why is force invariant under a Galilean transformation? [duplicate]

I've had a look around online, but I haven't been able to find something which answers this in a way I understand. Essentially, I'm trying to figure out why force is invariant under a Galilean ...
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### Reference frames versus coordinate systems

I have the following distinction clear in my mind: Reference frame → state of motion of the observer Coordinate system → set of numbers used to map the space points within a reference frame So for ...
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### Navier Stokes equations for rotating falling object

I am considering the problem of a rigid body moving in a fluid, free to translate and rotate (say, for example, a falling body in a fluid). Some of the approaches I found in some articles involve a ...
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### Can Newton's laws be reformulated with reference to “relative” frames

I was reading: https://arxiv.org/abs/1205.2326 page 2 which gives thorough discussion of the three laws. In particular there is a refutation of the (paraphrased) 2nd law implies the first because ...
If a block $m$ is placed on another block $M$ and a force $F$ is applied on bolck $M$. Then how many forces are acting on block $m$.(Friction is non zero) The image is taken from this site. Is ...