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# 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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### Why is it impossible to determine a real inertial frame?

Why is it impossible to determine a real inertial frame? We can determine the applied torque on a gyroscope by observing its precession. And thus we can evaluate the acceleration of our non-inertial ...
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### Movement of the Foucault pendulum

If my understanding of the Foucault pendulum is correct, then if I am in the northern hemisphere and if I let the pendulum oscillate in the north-south direction, then as the bob moves towards the ...
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### Query regarding parallel axis theorem

Suppose there are two points at (4,0) and (-4,0) each of mass 1 kg and the origin is (0,0). The rotational inertia of the combined system is 32kg.m^2. But if we shift the axis of rotation to left by 2 ...
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### What will happen to speed of my sound if I'am moving while producing sound? (animation included)

(The question is very ambiguous, here is the actual scenario I am talking about. I will rename the question, if its required in future.) If I am standing still and I produce a sound pulse in direction ...
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### What happens when you try to rotate a system around not it's center of mass?

What happens when you try to rotate a system around not it's center of mass?
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### Misunderstanding properties of principal axes for moment of inertia

My lecturer has stated that the principal axes of the moment of inertia (hereafter MOI) are a set of axes such that the off-diagonal deviation terms of the MOI tensor disappear. He then said that in ...
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### Rotate an object about the time axis

Is there a notion of rotating an object about its time axis? I'm not sure if this question totally makes sense, but it seems intuitive to me that an object with dimensions in the three spatial ...
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### How would centripetal and centrifugal forces vary in a rotating rod?

Suppose a horizontal rod (ignore gravity) of mass $m$ and length $L$ is rotating about one of its ends with constant angular velocity $ω$. Then, the tension must decrease as we move away from the axis....
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### Question about Euler's equation for rigid bodies

I wished to understand a particular case of Euler's equation applied in the following cylindrical body: where $I_{1,2,3}$ are the moments of inertia. By symmetry, $I_1=I_2=I_T$. Here I consider that ...
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### Time period of a simple pendulum confusion

While calculating the time period of a simple pendulum, i.e $$T=2\pi\sqrt{\frac{L}{g}}$$ Why do we consider the effective length, $L$? It is the distance from the point of suspension to the centre of ...