Questions tagged [relative-motion]

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3answers
33 views

Why is carrying a heavy object more taxing on the body than pushing the same object on wheels?

Where is the "extra help" coming from when rolling the object on wheels?
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1answer
117 views

Relative velocities problem ; how to draw useful diagrams if more than 2 things are changing?

Two students are canoeing on a river. While heading upstream, they accidentally drop an empty bottle overboard. They then continue paddling for 1.9 h , reaching a point 1.2 km farther upstream. At ...
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1answer
80 views

Is there anything in physics that is absolute rather than relative? [on hold]

Are there physical quantities that are absolute rather than relative? Things that do not depend on the reference frame? Perhaps I just haven’t learned about them yet. Original (before edit by @G....
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3answers
122 views

Relative velocity equation [on hold]

In rectilinear motion, to find the relative velocity of a car with respect to a train, we subtract velocity of the train from that of the car. We use this method when the car is moving on the road. ...
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2answers
103 views

Relativity and electromagnetic field

I have a question regarding Misner, Charles W.; Thorne, Kip S.; Wheeler, John Archibald (1973), Gravitation ISBN 978-0-7167-0344-0. It is a book about Einstein's theory of gravitation. At the page 79,...
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11answers
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If absolute velocity does not exist, how can we say a rocket accelerates in empty space?

If a rocket in space fires its thrusters, it is propelled forwards as per the laws of motion. This can be measured by its position relative to other bodies in the universe. Hypothetically if there ...
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2answers
79 views

Why can't we take space as universal frame of reference?

Suppose we have a ball filled half with water in space with nothing else around (nothing else in the whole space except the ball) and suddenly it accelerates for time t. obviously, there would be ...
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2answers
43 views

How can we define event to be proper and improper when there is no absolute frame of reference [duplicate]

Suppose in an empty space two rocketships exists with person A and B of same age inside each. Let A move with velocity c/2 away from B and return. They'll find out that B grew older while A didn't ...
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1answer
51 views

Why ball fall at same location from where we throw it? [duplicate]

I have a silly question. As we all know earth is rotates at a speed of 460 m per sec. So if I throw a ball in the air for 10 sec than the ball must fall 4600 m away from me but these does not happen ...
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0answers
14 views

Relative angle and velocity binning around one particle

Let's suppose particle positions and velocities are represented as $P_i = [p_x \; p_y \; p_z]$ and $V_i = [v_x \; v_y \; v_z]$. While, x,y,z represents the 3 components of position and velocity vector ...
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1answer
161 views

How can we find velocity, acceleration etc, of a revolving particle with respect to an observer inside the circle(not at center)

A particle is revolving in horizontal a circle of radius $R$ with constant speed of $|\vec{v}|$ and constant angular velocity $\omega$. There is another observer standing inside the circle, at a ...
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2answers
50 views

What are the necessary conditions for relative angular velocity to be defined? [closed]

I have certain doubts related to the definition of relative angular velocity .My textbook defines it in the manner given below:- $$\omega_{AB}=\frac{v_{AB}}{r_{AB}}$$ $\omega_{AB}$ is the relative ...
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1answer
49 views

Can we move without moving? [duplicate]

So here is the question, If I jump and hover over the ground for sometime why don't we move away from the point I jumped from? Because earth is rotating so if I hover long enough we should move from ...
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2answers
56 views

Meaning of the term speed of light in context of an object of non-zero mass

We know from GR that an object of non-zero mass cannot propagate at light. I have a problem with the term speed of light. Does it mean the relative speed of that object with another object or frame of ...
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1answer
191 views

Classical Relativity: Clarification

I am working on a problem that states: "A swimmer capable of swimming at a speed $c$ in still water is swimming in a stream in which the current is $u$ (which we assume to be less than $c$). ...
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2answers
229 views

Directions of static & kinetic friction?

Static friction : Static friction opposes relative motion between two surfaces. The car is moving at some tangential velocity relative to the road. Thus, static friction should act in the opposite ...
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1answer
683 views

Angular momentum about a moving point

I was used to see the Angular Momentum Principle as: $\dot{\underline{H}_O} = \underline{M}_O^{ext}$ that is, the change in angular momentum equates the external torque w.r.t. a point $O$. Now, I'...
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2answers
75 views

Would close to light speed travel be possible if all atoms in the system were instantly given “forward motion”?

I have heard people say that based on our current understanding and ideas for possible/current technology no person would ever be able to even travel at a solid (70-80%) the speed of light because ...
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3answers
140 views

Why cannot we determine our own velocity?

I know it would violate the principle of relativity. But have there been serious experimental attempts to contradict that principle? If I am in a moving train without windows and totally sound proof,...
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1answer
36 views

Interpretation of directional depenedence in special relativity

I am reading AP French's book, Special Relativity, because I have always wanted to understand the subject, and I have just attempted to answer the following question (1-22) in the book: An electron ...
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0answers
28 views

Question about relative motion by Galilean Transformation?

You are piloting a small airplane in which you want to reach a destination that is 750 km due north of your starting location. Once you are airborne, you find that (due to strong but steady wind) to ...
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3answers
62 views

Kinetic energy of an object

We know that motion is relative. So let an object(o) be moving with a certain velocity with respect to an object (A).If another object (B) is moving with respect to (A) at a given moment and they ...
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2answers
65 views

Is the weight of a bicycle frame significant compared to the body weight?

Some of my colleagues had a discussion about the question if the weight of a bicycle frame is significant compared to the weight of the rider‘s body. One argues that the weight of the frame can simply ...
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3answers
586 views

Motion of one body with reference to another

I studied that Galileo was punished by the church for teaching that the sun is stationary and the earth moves around it. His opponents held the view that earth is stationary and sun moves around it. ...
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1answer
138 views

Galileo's law of odd numbers

The Galileo’s law of odd numbers states that the distances traveled are proportional to the squares of the elapsed times. In other words, in equal successive periods of time, the distances traveled by ...
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1answer
147 views

Is this Question correct? Newtonian Motion - Relative Motion of Rain

There is a question in a textbook which states: "A cyclist is riding north at 12km/h when it starts to rain. The rain appears to be falling towards her at an angle of 10 degrees relative to the ...
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3answers
63 views

Sign conventions for relative velocity problems

I am having trouble solving relative velocity problems because I can't seem to understand the sign that goes along with the velocity of different objects. $$ v_{ac} =v_{ab} + v_{bc}. $$ How do the ...
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4answers
68 views

What is the correct formula for relative velocity?

I have consulted byjus.com, HC Verma and Khan academy, all are saying different. byjus and HC Verma book is saying that formula for relative velocity is $V_a +V_b$ but in Khan academy they are telling ...
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2answers
78 views

Throw a ball AT a moving train, in what direction does it reflect?

You are standing at a platform, with a ball. a train approaches and u throw the ball at it in a straight line from a small distance. in what direction des the ball reflect off? heres what i think, ...
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2answers
11k views

How insects got hits on the wind shield of a car?

There are rare chances when any insects got hit the wind shield of a car while driving in highway but it makes to wonder that how is that happen ? Does insect suffered a greater change in momentum ...
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2answers
10k views

Relative angular velocity and acceleration

Background: (Irodov 1.55) Two bodies rotate around intersecting perpendicular axes with angular velocities $\hat\omega_1,\hat\omega_2$. Relative to one body, what is the angular-velocity and -...
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2answers
559 views

The Meaning of Newton's Second Law of Motion Being Invariant Under Certain Transformations

What do we mean when we say that Newton's Second Law of Motion is invariant under Galilean transformations? Does it mean that the value of a force measured in one reference frame is the same when ...
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5answers
13k views

Speed of a fly inside a car

A couple of weeks ago I was travelling in a car (120 km/h approximately) and I saw a fly flying in front of me (inside the car, near my nose, windows closed). I wonder how was that possible. Does it ...
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1answer
59 views

Speed of light as the maximum speed and movement course

Assuming we have 3 objects d,e,f moving on the same line while e is stationary, d is moving to the left at 'almost speed of light' and f is moving to the right at 'almost speed of light'. What is the ...
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2answers
125 views

Does a helicopter that simply hovers remain in the same spot on earth? [duplicate]

Ignoring statistical variation in wind, will a helicopter that only applies force perpendicular to a perfectly sphere earth remain in the exact same spot relative to the earth? I am arguing with ...
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0answers
14 views

Issue deriving observed period of a moving signal in different reference frames

Consider a receiver on Earth measuring radio waves from an incoming slow moving UFO. Here is my attempt to find the period of the signal as measured by the earth observer. T' is the period of the ...
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1answer
33 views

Velocity of approach which changes continuously [closed]

There are two particles A and B which are moving with constant speed $v$ and $u$ such that $v$ is always directed towards B. At $t = 0$, the separation between A and B is $l$ and $u$ is perpendicular ...
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1answer
56 views

Time in Lorentz transformations

I have a question about the meaning of time in Lorentz transformations. When we say that event A for S' occurs at t', I understand that this ct' is a distance, but I wonder exactly what does it ...
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3answers
749 views

Relative motion involving angle

Suppose I am going in a direction with a velocity $v_1$ and my friend is going in a direction which makes an angle of $A$ with my direction with a velocity of $v_2$. Then what will be my relative ...
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2answers
51 views

Throwing/Dropping an Object

When we throw or drop an object while moving, do we impart it our acceleration or velocity or both? Say i throw a ball at 5 m/s (relative to me) while at say, 30° to my direction of motion, then will ...
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1answer
66 views

Moving moon explanation

I saw the moon moving in a fast pace several times with the naked eye, even during day time when its cloudy. How is that possible? I asked my teacher about it and he said its just an illusion, but ...
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4answers
157 views

Question about spinning Earth

The earth spins on its axis at 1674 km/h from west to east. Would it not imply that an airplane flying eastbound at 500 km/h would cover a distance of 500 kilometres in an hour while another plane ...
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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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0answers
24 views

Vertically move in a helicopter to go somewhere on Earth [duplicate]

Is it possible to go from point A to point B (which are on same latitude) by hovering above A and wait till the earth rotates to point B below and then come down vertically? I believe there would be ...
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11answers
30k views

If all motion is relative, how does light have a finite speed?

I've often heard that Einstein shattered the notion of absolute motion (i.e. all things move relative to one another) and that he established the speed of light as being absolute. That sounds ...
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3answers
40 views

Defining what it means for a reference frame to move with a velocity $\mathbf{u}$ with respect to another

In describing a Galilean transformation, for example, one might say that if a reference frame $S'$ is moving at a velocity $\mathbf{u}$ with respect to $S$, then an object traveling at a velocity $\...
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2answers
57 views

Relativity: moving space shuttles [closed]

Two space shuttles $A$ and $B$ are moving in opposite directions. A person on Earth measures $v_A = 0,75 c$ and $v_B = -0,85 c$. What is the velocity of $B$ relative to $A$ (= $v_{BA}$)? So my first ...
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1answer
84 views

Time when two particles will meet [closed]

Particle P moves with constant speed of 13m/s always aiming at O . As P starts moving , O moves with constant velocity of 5m/s towards positive y-axis. Time taken by particle P to catch O will be? I ...
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0answers
24 views

Time interval to closest approach between two sattelites [closed]

Two artificial satellites are in circular earth orbits in the same plane. The orbit radius of one of the satellite is $r$ and that of the other is slightly greater than the other i.e $r + \Delta r$. ...
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1answer
123 views

Relative motion with two observers

For four particles A, B, C, D , the velocities of one with respect to other are given as $ V_{DC}$ (Velocity of D with respect to A) is 20 m per second towards north, $ V_{BC}$ is 20 m per second ...