Questions tagged [relative-motion]

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How does time dilation work with relativity

It has been started quite often that you can only determine if an object is moving relative to a point you select, and that space itself can not yield any such reference frame. Couldn't you, however, ...
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Is there some kind of aether for rotations only?

Currently I'm reading "A briefer history of time". I understand how the Michelson–Morley experiment refutes the theory of an aether (like in "absolute frame of reference") for translation in space and ...
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1answer
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solving a two body problem using relative motion and reduced mass

I'm having a hard time trying to understand fully this topic and how reduced mass and relative velocity should be used. Let's say we have some sort of mechanical problem regarding the interaction (or ...
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2answers
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Relative velocity in two dimensional motion [closed]

I came across the following problem in my textbook: "Two particles A and B are projected in air. A is thrown with a speed of 30m/s and B with a speed of 40m/s as shown in the figure. What is the ...
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2answers
184 views

2 dimensional relative motion

I came across the following question: Airplanes A and B are flying with constant velocity in the same vertical plane at angles $30°$ and $60°$ as shown in the following figure. The speed of A is $...
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1answer
466 views

Is it necessary that the path of an object in uniform motion is a straight path? [closed]

What does the path of an object look like when it is in uniform motion?
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2answers
470 views

Motion of uniform accelerating rocket in special relativity

I have been trying to learn more about acceleration in special relativity. For the purpose I consulted the great Lev Landau. He has an example about this in his book but one of his equations puzzles ...
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1answer
482 views

Angle made by bullet in a different frame of reference

I did solve this question, though I did not understand it completely due to the flow of the same type of questions, its language, and one other thing bugged me which I will be stating after the ...
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1answer
1k views

Falling hailstones on windscreen

Two motor cars have their wind screens at $\theta_1=15^{\circ}$ and $\theta_2=30^{\circ}$ respectively. While moving in a hailstorm the drivers see the hailstones bounced by the wind screen of their ...
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1answer
185 views

How does relative velocity change when there is a translation of axes?

I was going through a textbook (Hibbeler, Engineering Mechanics: Dynamics 14th ed.) and the following passage stumped me. The chapter was on the relative motion of two particles using a translation of ...
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1answer
53 views

Retrograde Watches [closed]

I am not a physicist and not familiar with physics that much.I have a watch which has Retrograde motion. I have read about what is ...
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2answers
176 views

Induced motional EMF where the wire is stationary and the field source is moving?

If a wire is moving in a magnetic field $B$, there is a Lorentz force acting on both the postive and negative charges, separating them to create an electric field, which is a great explanation to aid ...
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3answers
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How high do you need to be so as to not rotate along with Earth?

So, I saw this meme about some minister commenting that the Earth doesn't rotate, for if it did then planes only need to be in the air and the destination city would come to it. I know this is absurd ...
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1answer
83 views

Can an object take off from A, do not move (in the air) but land at a different place? [closed]

Can an object take off at a point A on the surface of the Earth and then land after some time only to land at a different place where it initially took off (because in the mean time the Earth has ...
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3answers
263 views

Momentum and relative motion

To calculate momentum, $p=mv$, you must know the value of $v$. However, since all motion is relative, there is no abslute value for $v$. So, what is it you are actually calculating? It seems like the ...
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1answer
291 views

How to estimate the relative motion using kinematic equations?

Background I am reading the following thesis: Todosiev, E.P., 1963. The action point model of the driver-vehicle system. On page 9 it describes the relative motion between 2 cars as follows: $...
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1answer
501 views

In Einstein's “relativity of simultaneity” thought experiment, would not the passenger on the train see a dimmer signal? [closed]

This is the updated, more precise question--is this a paradox?: Suppose a rocket traveling close to the velocity of light which emits a single photon from its midpoint at point A, illustrated ...
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2answers
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How can you accelerate without moving?

I know this question has been asked in other forms, generally regarding the balance of forces. This time I want to focus on motion. I've got a laser accelerometer on my desk. It tells me that I'm ...
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3answers
345 views

What would happen if a ball flew through the open window of a car?

I asked a science teacher this question a while ago but I did not receive a clear answer. Now, I was hoping someone on this Physics site could shed some light on my conundrum, I've been wondering for ...
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1answer
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What happens if you fly a drone inside moving passenger airplane? [duplicate]

I have a little question. If I mark an X in the center of a passenger airplane, and try to fly a drone from the X mark in the moving passenger airplane (800-900 km/h), what will happen to the drone? ...
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1answer
792 views

What is my acceleration in my own frame?

This is , I suppose not a good question , but I think I am missing something which confuses me in this question. So my question is - Velocity is relative. So suppose a car is moving at a speed 200 ...
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5answers
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Air flight and Earth's rotation

I read a response asking why flights of equal distance east and west take roughly the same time (disregarding wind actions). I have trouble visualizing part of the answer; "the speed of the rotation ...
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5answers
3k views

Is it possible to stay up while riding a bike on a moving sidewalk without actually moving?

If I ride a bicycle on a moving sidewalk so that I am not in effect moving at all relative to the ground, will I fall over?
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1answer
656 views

Calculating relative velocity in three dimensional space

Given two points $\mathcal{A}$ and $\mathcal{B}$ in $\mathbb{R^3}$ whose position and velocity vectors are, respectively: $$\mathbf{r_A}=\begin{pmatrix}r_{A_{x}}\\r_{A_{y}}\\r_{A_{z}}\end{pmatrix}$$ $$...
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1answer
124 views

Why does the classical Doppler formula make a distinction between movement of the source and movement of the receiver?

I've tried rewriting the Doppler formula to include only the relative velocity between the source and the receiver of sound waves. However, when I compare the results with the results of the formula ...
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1answer
130 views

Why doesn't the changing field of a moving charge create EM waves? [duplicate]

EM wave phenomenon is usually described as "changing electric field creates changing magnetic field which creates a changing electric field etc." But fields of a uniformly moving (not accelerating) ...
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3answers
7k views

How can planes land on a rotating Earth?

If the earth is rotating (e.g. at 1000km per hour, at the equator), how can planes safely land on a moving runway?
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2answers
102 views

energy of the system increasing after acceleration (one reference frame)

The system consists of small mass $m$, large mass $M$, and chemical potential energy $E_{chem}$, as shown in below image, the reference frame is following the small mass throughout. The total energy ...
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5answers
343 views

Airplane on a treadmill - Variant Thought Experiment

This thought experiment is in a way related to the (in)famous airplane on a treadmill problem. If you take a ball and place it on a treadmill, will the ball: Move backwards relative to the ground at ...
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4answers
1k views

What do observers in relative motion agree on?

What are the measurements on which two observer in relative motion will agree? Other than the speed of light.
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2answers
662 views

How can I find the maximum height if I have changing acceleration?

I'd like to find the maximum height that a projectile reaches in motion if I have a non-constant acceleration. How would I do this? What variables do I need to know in order to calculate this? ...
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2answers
499 views

Is polar coordinates frame non-inertial?

Consider the acceleration expressed in polar coordinates. $ \left( \ddot r - r\dot\varphi^2 \right) \hat{\mathbf r} + \left( r\ddot\varphi + 2\dot r \dot\varphi \right) \hat{\boldsymbol{\varphi}} \...
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1answer
246 views

Special Relativity and Composition Law for Velocities with respect to an observer watching two objects moving away from a central point

So I understand that special relativity is all about the frame of reference and there is a lot to do with time dilation and how space-time is warped at velocities near $c$. So my question is what ...
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4answers
774 views

Ball dropped from train [closed]

A ball is dropped of a train traveling with high velocity, to a man standing near the track, the bank A) falls down vertically B) moves horizontally C) follows an elliptical path D) parabolic ...
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2answers
432 views

Find the relation between length of pulley and strings [closed]

A pulley is pulled with external force $F$. $x$ and $y$ denote the displacement of two ends of strings of the pulley and $z$ is the displacement of the pulley. Prove That $$z = \dfrac{x+y}{2}$$...
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5answers
700 views

Why was it difficult to walk in the same direction the train's acceleration, and easier the other way around?

The other day while I was walking in the same direction that the train was accelerating. Then I came across this question. Please if would answer it, I am very curious to know. But when I walked the ...
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1answer
348 views

Objects travelling relatively to each other faster than light?

When we say that something is travelling a certain speed, it's really travelling that speed relative to the Earth. When saying the speed of anything, it is, for the most part, relative to something ...
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1answer
122 views

Kinetic Energy: Difference in energy for observers [duplicate]

Consider a stationary 10kg bike; if I apply a force of 10J then $KE=\frac{1}{2}mv^2$ so $v=\sqrt\frac{2KE}{m}=1m/s$. If we consider the same example again, but from the point of view of a stationary ...
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1answer
3k views

Doppler: how to derive formule “source moving” from formule “observer moving”

A question like this has already been asked, with a satisfying explication (the relative motion of the source and the observer with respect to the medium (air) is different), but without a derivation ...
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0answers
40 views

Disappearing galaxies [duplicate]

According to the cosmological model of the expanding universe, the distant (diametrally opposite) galaxies have bigger and bigger relative comoving speed, and this speed (which is not a relative speed ...
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3answers
334 views

Is General Relativity compatible with relative speeds bigger than $c$ between two inertial frames?

My question is motivated by a remark done by Tegmark in his book "Our Mathematical Universe". He says that GRT does not prove that relative speeds between material points are always smaller than c. It ...
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1answer
149 views

Could a gyroscope demonstrate absolute motion?

If a spaceship were moving very fast, and a rocket motor mounted perpendicular to the direction of motion/"main thruster" were turned on, the change in direction to an observer would be proportional ...
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1answer
63 views

question from the idea of relative acceleration [closed]

the accelerations of a particle as seen from two frames $S_1$ and $S_2$ have equal magnitude $4 m/s^2$ so my teacher said that the acceleration of $S_2$ with respect to $S_1$ may be anything between ...
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0answers
46 views

Direction of motion 1 [closed]

A man on a bike travelling east on straight road at 8km/h sees a car driving north at 60km/h. What is the apparent speed and diretion of motion of car to the cyclist?
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567 views

One dimensional motion - Why does a ball fall back in my hands when I throw it up in a moving bus? [duplicate]

Suppose you are moving in a bus and you throw a ball upwards. Why does it always land in your hand and does not fall behind you? The bus is moving with a uniform velocity in a straight direction. Now ...
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1answer
193 views

While jumping in a high speed train why we fall on same place? [duplicate]

while we jump inside a high speed train why do we fall on the exact place? as train is in high speed and we are jumping so we should fall backside. but this doesn't happen why?
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1answer
90 views

An ambiguous question on 2 balls [closed]

Two balls A & B are at rest at the bottom of a hill.Sometime after ball A is given a kick up the hill, ball B is also given a kick up the hill. When ball B is going up the hill, ball A is already ...
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1answer
212 views

Can absolute speed be determined by an object's mass?

It's been said that nobody can actually know how fast the Earth is moving through space, because a reference point is needed to determine absolute velocity. But if mass increases as speed increases, ...
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1answer
168 views

Is light relative? [duplicate]

I was wondering, if two cars (A and B) are going at different velocities let's say A=90km/h, B=80km/h then if we add the two speeds we get 170km/h meaning they are relative to each other. But if one ...