# Questions tagged [relative-motion]

Use this tag for questions related to how objects move relative to other objects dependent on your frame of reference, and how this applies to special relativity.

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### Question regarding friction acting on a disk on a conveyor belt [closed]

I have the following problem on which i am working A horizontal conveyor belt is running at a constant speed of $v_b = 3.0\hspace{1mm}m/s$. A small disc enter the belt moving horizontally with a ...
1 vote
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### Confusion about sign conventions used in the Doppler formula

Wikipedia gives the Doppler formula as: $f = \left( \frac{c \pm v_r}{c \pm v_s} \right) f_0$ c is the propagation speed of waves in the medium. $v_r$ is the speed of the receiver relative to the ...
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1 vote
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### In an ideal situation, why should no friction exist when an object rolls? [duplicate]

As per my textbook, “a body like a ring or sphere rolling without slipping over a horizontal plane will suffer no friction in principle. At every instant, there is just one point of contact between ...
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### How to calculate the relative speed when three bodies are involved? [closed]

Two trains A and B start from a station and move in parallel tracks with velocities 40 kmph and 60 kmph respectively. A man sitting in train A. watches a lady who walks inside the train B at a speed ...
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### What effect would relativity have for an objective with absolutely no momentum? [closed]

I know as you near the speed of light time slows down and mass increases to near infinite. What I'm curious about is what would happen if an object lost all momentum. No movement at all not even the ...
1 vote
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### Straight wire in moving uniform magnetic field induced emf

My question is a follow-up to this one. The green dotted line is the arbitrary loop which is constructed in the calculation of emf in the wire of length L. x is a variable which can be changed to ...
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### Pseudo Orbital motion only due to Coriolis force

Planet, say of mass M and radius R is rotating with some angular velocity ω and a object of mass m (initially on the surface and rotating with the planet) was launched with velocity v vertically ...
1 vote
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### Does relative velocity apply before or after the impulse?

I'm solving the following question from Kleppner and Kolenkow: My solution differs from the textbook solution not only in the magnitudes in parts (a) and (b) but also the conclusion in part (c). ...
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### If an observer was trapped in a closed box with no way to interact with the external surroundings how will he know if he is moving or at rest [duplicate]

I am a high-school student. Recently we learned the concepts of relative motion and velocity. The idea that anything in motion can subsequently be at rest depending on the frame of reference ...
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### How Fast Must a Man Run to See Rain Falling horizontally?

The fact that tan 90° is undefined indicates a key issue in the problem. Does this mean it is impossible to observe rain falling at 90 degree? When rain is observed to be falling at 90° with the y-...
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### With what vel. would you have to launch an object vertically up from the earth's surface for it to land back again at it's initial launching point?

[Can skip reading this part] First of all, Newtonian gravity shall be considered whilst trying to solve this question. It's been on my mind for a long, long time and has been bothering me since. I ...
1 vote
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### The stupidest question ever on relative kinematics and angular velocity [duplicate]

I am scratching my head on a very basic formula whose meaning escapes my intuition. On basically all texts of mechanics the following result is derived: Suppose that a rigid body is moving with ...
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1 vote
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### Euler Rotation Equations and invariance of vectors in different reference frames

Consider two frames, one which is inertial and the other one rotating w.r.t. to the inertial frame. Say there is a rigid body having angular momentum which is same/invariant in both frames. How is it ...
1 vote
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### How does relative motion work for an extended object?

I have this conceptual doubt which might be flawed very badly but I don't understand this particular thing. For example, if one end of a stick is moving with velocity $v_1$ and the other with $v_2$, ...
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### Does relative motion allow for speeds $>c$?

If motion is relative, (so if X was stationary and Y was moving at v m/s, we could think of this as Y being stationary and X moving at -v m/s), could we not create a scenario in which a stationary ...
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### The locus of the velocity vectors of a boat navigating in the sea under the presence of a very strong wind?

I already asked a question very similar to this one here and I think the solution would not work when the boat navigates in the sea when a very strong wind blows. That is I am trying to find the ...
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### Photon shot in opposite direction of spaceship, what is its relative velocity? [duplicate]

Okay, lets say you have frame S which is a spaceship who is travelling with speed v = c/3 relative to S' which is some planet Y. In the spaceship two photons are shot in opposite direction, to the ...
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### Calculating relative velocity: What am I doing wrong? [closed]

There are two objects A and B. Points P1, P2, P3 are in the same line, and P2 is exactly at the middle of P1 and P3 Suppose B is moving at constant velocity along the line P1 to P3. Thus, time taken ...
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### Determining the time elapsed between two events in

I want to determine the time a photon needs in order to cover a distance, say $l_0$, where $l_0$ is the length of a spaceship (reference system S'). So, the photon is going from one end of the ...
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### The distance problem [closed]

Say a car has to move from Point A to Point B on the surface of the earth. The car starts from rest at Point A at time $t=0s$ reaches point B at time $t=10s$ with a constant velocity of $1000 m/s$. ...
1 vote
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### Coordinate transformation and absolute motion in general relativity

In special relativity, all motion is relative. But in the presence of black hole, all motion is with respect to black hole. The curvature of spacetime depends on how far we are away from the black ...
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### Special-Relativity and how things not accelerating appear to be the same in all frames of reference [duplicate]

As someone who knows very little special-relativity (and none of the math) I understood that if you take a car moving down the road (at constant velocity) and approaching an observer, there is no ...
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### Conceptual meaning of frame of reference for kinetic energy

what does the statement The speed, and thus the kinetic energy of a single object is frame-dependent (relative) even mean? does the impact of a collision of moving bodies and henceforth transfer of ...
1 vote
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### Attempting to solve the twin paradox without acceleration

My teacher told me that the key to solve the twin paradox is acceleration of the one that travel away. However, I feel a little bit uncertain that time change significantly by just a slightly nudge of ...
1 vote
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### Wording of Relative Velocity problems [closed]

I've been doing some relative velocity problems. The three main types I do are to do with cars, boats/rivers and planes/crosswind. I'm fine with cars as the wording is pretty straightforward - it is ...
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### To find the displacement of a rolling body

When calculating the displacement of a rolling body do we just calculate the displacement due to Vcom in a particular time t or additionally need to consider also the displacement that may be produced ...
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### Accelerating body in a non-inertial frame of reference

If a body is subjected to a force, can I find a non-inertial frame of reference in which the body is not accelerating?
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### How does one interpret the relative motion of an object in orbit as it compares to to the object it is orbiting?

How does one interpret the relative motion of an object in orbit as it compares to to the object it is orbiting? In flat spacetime, it's pretty easy to determine relative motion. If Alice sees Bob as ...
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### Time Dilation and Spinning Reference Frames

If a spaceship approaches a rapidly spinning planet, would the planet's inhabitants , the inhabitants of the planet where the spaceship came from , and the spaceship's occupants observe time dilation ...
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### Is it possible to detect your speed relative to light? [duplicate]

Let’s take two cases: (1) your velocity is constant and (2) you are accelerating. (1) isn’t the answer no, like that’s a core idea of Einstein’s relativity stuff? (2) I don’t know.
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### Rotating Reference Frames And Their Phenomenon

In a rotating reference frame, while observing the proper motion of stars due to your spin, would you perceive time dilation when closely observing those stars?
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### Why is throwing a bullet by hands not effective as using a gun? [duplicate]

The bullet when fired applies equal and opposite force to the Gun, (Newton's 3rd law) Thus to keep the gun stable we apply some force which should be equal to the force applied by the bullet. If we ...
1 vote
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### Is all change movement? [closed]

Is there a change in the universe that cannot be reduced to movement? One counter-example should be enough. :) Heat is a type of change that was once thought to be qualitative, but is now realized to ...
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### Velocity of Separation and Relative Velocity

I have some problems in understanding a concept, which has been used in the problem in the picture: I don't understand what are we actually using to solve this question. Are we using relative ...
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### Trajectory of light send from a moving box [closed]

In a closed box in inertial motion a ball bounces up and down vertically. Apart from this movement, the ball is motionless relative to the box. The trajectory of the ball seen by a stationary observer ...
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### Is there a Doppler effect measured on the sunlight depending of the seasonal position of the Earth regarding the motion of the Sun through space?

The whole question is mentioned in the title but here I would add the conjecture that I am affraid that the answer(s) should be similar to a possible question about Michelson and Morley experiment...
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### In galilean relativity, is an observer assumed to be at rest only to simplify calculations, or is there a physical reason for this assumption?

I am a beginner in Physics and my teacher taught us "Relative Motion" yesterday. He said that the "Observer is assumed at rest." Is the observer assumed to be at rest only to ...
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### Does kinetic energy rely on the observer mass too since velocity is relative?

There is no 'correct' inertial reference frame according to relativity. Objects are only 'in motion' relative to an arbitrary inertial reference frame. So let us take the following example. A person ...
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### Do released objects take the direction and speed of their parent frame's velocity, or just the parent frame's speed component?

Context: I'm working on a space game. I noticed that an unpowered object fired from a strafing spaceship appeared, as the released object moved, to curve in the direction the ship was strafing. This ...
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### Location of an object in empty space [closed]

Is it correct to assume that if there is only one object in the void (really empty void), then its location (the answer to the question “where” this object is) cannot be established? You need at least ...
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### Simple classical mechanics problem to compute minimum distance attained between two ships moving with constant velocity

I have been reading the book "A Course in Classical Physics 1 - Mechanics" by Alessandro Bettini. I have reached a problem in the first chapter that I am having trouble with. The problem ...
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