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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Rutherford's scattering formula center of mass vs laboratory frame
I am trying my best to mathematically derive the transformation of Rutherford's scattering formula from center of mass coordinates
$$
\frac{\text{d}\sigma}{\text{d}\Omega}(\vartheta_{\text{c}}) = \...
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How the spins up and down change for an accelerated observer? [closed]
For a accelerated observer the transformations of $|0>$ and $|1>$ are as follow
$|0>=cos(r)|00>+sin(r)|11>$
$|1>=|10>$
the first spin of right hand is in the Rindler rigion I and ...
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Conservation of momentum and energy: what is considered to be the system?
In an inelastic collision where mechanical energy is not conserved, momentum is still conserved. Should the Earth or the ground be considered as part of the system in order to account for the ...
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Question on an Exercise from Meriam, customized questions [closed]
I'm struggling to solve this problem:
.
My teacher told me that we should use the theorem of the moment of inertia and the Center of Mass.
The given instruction are the following one:
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What axis of rotation should be used for rotational kinetic energy?
I know the kinetic energy of a rigid object is
\begin{align}\tag{$1$}
KE = \frac{1}{2}mv^{2} + \frac{1}{2}I\omega^{2}
\end{align}
where $v$ is the velocity of the center of mass of the object, $\...
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Rotation of the plane of oscillation of the Foucault pendulum
If the plane of oscillation of the Foucault pendulum rotates due to the Coriolis effect, shouldn't the rotation be counterclockwise in the Northern Hemisphere, similar to the rotation of tornadoes? Or ...
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The forces exerted by an electromagnetic field on a moving charge
Consider a charge $q$ moving in a uniform magnetic field $\vec{B}=B\hat{y}$. The initial velocity of the charge is $\vec {v_{0}}=v\hat{x}$ ($v$ is a constant). Due to the magnetic field, the charge ...
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Intuitive idea behind the torque about a point
The text defines the torque of a particle system as being connected with the axis of rotation. "Taken two particles of masses m connected to a thin rod of negligible mass etc", but later ...
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Which physics is true based on different reference frames? [duplicate]
There is one movement action based on two different reference frames.
I’m moving to a fixed wall with velocity $v$ if we take the ground as a reference frame, and I hit the wall and stopped.
The ...
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Optic Fiber Gyroscope Within Its Frame
I understand why the fiber optic gyroscope works as well the calculations for the time discrepancy between the beams travel time, but only as observed from out side the ring, "watching" it ...
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Relative velocity in the air frame or platform frame?
In "Introduction to Classical Mechanics: With Problems and Solutions" by David Morin he describes the following scenario:
Let $ v_s $ be the speed of sound in air. Imagine two people ...
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Spin Connection, Killing Equation and Spinors under Diffeomorphism
Under a diffeomorphism $dx'^{\mu}=\frac{\partial x'^{\mu}}{\partial x^{\nu}}dx^{\nu}$ we have that the components $A_{\mu}$ of every 1-form $A=A_{\mu}dx^{\mu}$ transform as: $A'_{\mu}=\frac{\partial x^...
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Does going in circles really fast desync your clock? [duplicate]
I'm thinking of 4 similar scenarios. In all scenarios, Alice and Bob are in open space, relatively close to each other (meters/kilometers apart), and using special spaceships with special thrusters ...
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Regarding the motion of center of mass [duplicate]
When writing the equations for center of mass we assume as it to be the point where all the forces act and write the corresponding kinematic equations, and in doing so we dont assume any distribution ...
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Correct Lagrangian for classical central force problem?
Wikipedia gives the following Lagrangian for central force problem:
$$\mathcal{L}=\frac12 m \dot{\mathbf{r}}^2-V(r)$$
where $m$ is the mass of a smaller body orbiting around a stationary larger body. ...
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Force not applied on center of mass
I have a question about rigid body motion when a force acts on off-center of mass.
I read the answer to the post force applied not on the center of mass but I'm still confused.
I understood that ...
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Lorentz boost in curved spacetime
In Minkowski space, Lorentz boost is provided by the vector field
$$b^{\mu} = a(x \partial_t - t \partial_x)$$
for some arbitrary constant $a$. The integral curves of this gives the trajectory of an ...
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The Frame of Reference of Light [duplicate]
According to my current understanding of special relativity, light would not 'see' the universe's time tick. In other words, the universe would remain a snapshot in time according to a photon from the ...
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Is there any physical difference between a receding body and a moving body? [duplicate]
Edited version.
A body $A$ is receding at acceleration $\vec {a}$ with respect to a point $P$ because of the expansion of the universe.
Another body $B$ is accelerating at the rate of $\vec{a}$ with ...
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Torque about an accelerating point
The total force acting on the pulley is zero so:
$$F = mg + T_1 + T_2 \tag{A1}$$
Analyzing the torque and angular acceleration about the actual axis of rotation, the axle
of the pulley, gives:
$$τ_{...
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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 ...
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Combined torque of torques at different points
Let's say we have a constant (homogene) magnetic field $\boldsymbol{B}$ and a rigid object. Now let's say there are magnetic dipoles $\boldsymbol{p_{m,1}}$, $\boldsymbol{p_{m,2}}$,... $\boldsymbol{p_{...
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Moment of inertia of solid cone [closed]
Can we compress a solid cone parallel to the axis of rotation, into a disk of same mass to find moment of inertia of solid cone (uniformly dense)?
What I think...
As we are compressing the cone ...
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Is the conservativity of a force frame independent? If so, how do you show it?
If a force $\vec{f}$ is conservative in a frame $S$, is it such in another, generic, frame of reference $S'$? How do you show this, and how are the potential energies in the two frames related?
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Is the elementary work of a force frame independent?
(This is a classical-mechanics question)
Sorry for the trivial question. A force $\vec{f}$ doesn't depend on the frame of reference; however, the work $W$ done by $\vec{f}$ is, in general, a quantity ...
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Does a charged particle moving in a static electric field experience an EM wave?
If a (varying) force was applied to a charged particle such that it moved towards the (point) source of a static electric field at constant velocity, would that particle in its reference frame ...
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Trying to confirm that the trace of the energy momentum tensor divided by the energy density is NOT invariant
I am analyzing this question in the FRW universe with a perfect fluid.
The trace of the energy momentum tensor $$T^{\mu \nu} g_{\mu \nu} = \rho - 3p $$ is of course an invariant quantity. It does, ...
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Angular momentum of $N$ particles
I am reading Goldstein's Classical Mechanics book; I have difficulty understanding these lines. Why do the last two terms vanish? I am reading this and thinking $r'$ is a null vector, but the second ...
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How to prove: Are perpendicular coordinates (wrt to relative velocity) unchanged (or only scaled) while deriving the Lorentz Transformations?
Thank you for helping with this question and I'm sorry if it's kind of stupid.
TLDR: In many textbooks and other derivations deriving the Lorentz Transformations, they omit coordinate axes orthogonal ...
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Cases where centrifugal and coriolis forces are applicable
I'd like to ask my query through 2 case examples:
Case 1) Suppose a person whirls a stone tied to a string in a horizontal circle around him such that he/she is always pointing and looking towards ...
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Couple force in a rotating steel ruler
I learnt that pure rotational force can be caused by only couple force , two forces acting in opposite direction which are equal in magnitude in 2 different points at a system.
But I am trying to ...
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Why is the torque of a rolling hexagon about axis equal to 0? [closed]
In the International Physics Olympiad problem 1998: rolling of a hexagonal prism:
it states that conservation of angular momentum is applicable since the total external torque is 0. How is this the ...
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Is work done relative according to the theory of special relativity?
I performed a thought experiment.
Consider a body $A$ and another body $B$.
Body $B$ is moving at velocity $v$ in direction $x$ with respect to $A$. This implies that body $A$ is moving at velocity $v$...
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Sabine Hossenfelder says time dilation is due to acceleration in the twin's paradox. Is this true?
Sabine Hossenfelder says time dilation is due to acceleration in the twin's paradox. Is this true?
At 12 minutes into this video https://www.youtube.com/watch?v=ZdrZf4lQTSg, Hossenfelder states, &...
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Is momentum conserved relative to all reference frames?
Assuming that there is an observer S in a train that is equipped with a cannon moving to the right relative to another observer S' in a train moving to the left relative to S, which is also equipped ...
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Motion of a bead along a frictionless rotating rod (constant angular velocity along one of it's ends, which is fixed [duplicate]
There's a horizontally placed rod, fixed on a vertical axis at one end, so it doesn't fall on the ground with acceleration $g$, and stays horizontal, there is a bead (mass $m$) near that end point ...
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Invariants from the covariant derivatives of a scalar field
I am reading Theoretical minimum: Special Relativity and Classical Field Theory where you construct a Lagrangian for the field by the argument that it would be invariant under the Lorentz ...
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The use of centrifugal force in highschool physics classes [closed]
I am a retired theoretical physicist in the Netherlands. I am currently trying to promote the exact sciences by helping highschool students with their mathematics, physics and chemistry studies.
I am ...
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If energy is relative, then how it can remain conserved?
If energy depends on frame of reference of observer, then how it can remain conserved?
Same question also for linear and angular momentum.
I think energy is conserved when seen from a specific frame ...
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What happens if you're on a spaceship accelerating close to the speed of light, but then stop accelerating?
So most people want to ask what happens if you go super-close to the speed of light and try to go a bit faster. I want to know what happens if you stop accelerating at close to $.99c$. Not decelerate, ...
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In what frame of reference are the Euler and Lagrange time derivatives taken in?
In what frame of reference are the Euler and Lagrange time derivatives taken in?
I am beginning to study fluid mechanics, and there is a conceptual problem that I just can't shake. If you have a field ...
