Questions tagged [distance]

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Is this $x$-$t$ graph possible? Is the distance decreasing over time in this graph?

I have read in a Book: But I think it is possible as a Negative Velocity and Positive Acceleration: Reference: SL Arora Physics Class 11, Pg No. 152.
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1 answer
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How to find distance between colliding objects?

Consider an object A with mass m with velocity v collides with another resting object B with mass M. After colliding we know that after some time both the objects will gain same velocity. But a ...
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1 vote
1 answer
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Is it possible to determine the distance between the earth and a star by only studying the light emitted from this star?

I was reading about the Doppler shift and how we can measure how fast something is moving through its Doppler shift. This got me thinking is their a way/formula to measure the distance between us and ...
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-1 votes
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Calculate Speed From An Accelerometer to get meters per second

We are trying to calculate speed in meters per second from an LIS2DH accelerometer. We get ax,ay,az at regular intervals. I have read many posts about calculating the data, and taking an average over ...
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2 votes
3 answers
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Free Fall and constant acceleration

Although the acceleration of free fall is constant, why don't the distance go like $y = 9.8+4.9= 14.7m$ after 2 seconds, $y= 19.6+14.7 = 34.3m$ after 3 seconds? I think Constant acceleration work like ...
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6 votes
4 answers
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Finite distance, Infinite time?

Let's say that a ball dropped from $1 \ \text{m}$, covers $\frac{1}{n^2} \ \text{m}$ for every $n$ bounce, i.e $\sum_{n = 1}^{\infty} \frac {1}{n^2}$ so the total distance will be $\frac{π^2}{6}$, ...
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How to find velocity as a function of distance/time when force is given as a function of distance?

Let's say force between two particles is given as F=k/r² where 'r' is distance between two particles and k is a constant. I am having trouble in finding velocity as a function of distance between ...
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3 votes
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What is the matter/energy flux on the cosmological horizons?

Consider the usual standard FLRW cosmology. Depending on the model, there may be two distinct horizons around any local comoving observer: the particles (or causality) horizon and the event horizon. ...
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How to calculate Proper Distance as an arc length in Schwarzschild metric?

I am trying to determine the method to calculate proper distance with constant time and radius in Schwarzschild Geometry. With only $\theta$ and $\phi$ being variable. I think it involves integrating ...
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2 answers
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How to find time taken for a faster object to cross a slower object of same length, both moving parallel to each other in the same direction? [closed]

Can you explain me how to determine the time taken for a faster object to cross a slower object when they're both of same length and are moving parallel to each other in the same direction?
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2 votes
1 answer
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Is redshift an accurate method for measuring distances of distant galaxies and quasars?

I'm currently in 11th grade working on a science project about measuring distances using redshifts. I understand how the wavelength of a light wave increases when an object moves away from the point ...
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1 answer
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Comoving distance in $\Lambda$CDM - Understanding an approximation

I am trying to find the comoving distance, $$\chi = c\int_0^z \frac{dz}{H(z)}$$ for the $\Lambda$CDM model (spatially flat universe, containing only matter and $\Lambda$). $$H^2 = H_0^2[\Omega_{m,0}(1+...
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Distance to source of GW 150914

Looking at the original paper on this gravitational wave, PRL 116, 06112 (2016), it is difficult to determine how they estimated the distance to the source. Can anyone provide some explanation? They ...
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1 answer
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Formula for work done for both conservative and non-conservative force are different?

We know that the formula for Work Done by an constant force is W.D = Force x displacement x (cosine of angle between force and displacement). Situation: A mass m travels 10 meters towards  +ve axis ...
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1 answer
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Can anyone guide me on torque equation to rotate a part?

hope you all are doing good. I am a bit confused on which equation to use to calculate the torque required to rotate a part. I want to use a hydraulic motor at the 6th axis (end of robot arm) of ...
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1 answer
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Why are people using 'lightyear' as a measurement of time? [closed]

I came across 2 people in an open forum, who are college students, who that agree using the term 'lightyear' as a measurement of time is correct. Their context was "This country's technology is ...
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1 answer
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Thought experiment with the speed of light

Every time we look at a star we are looking to the past. That's because the light of that star needed to travel long distances at the speed of light. When the light reaches our sight maybe the star no ...
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An easier way for me to calculate the distance , But does it always stand true? [closed]

When can I say that the distance is equal to $d=\int^{t_2}_{t_1}|V|dt$ , Where V is the velocity and it's given in terms of time and $t$ is the time , You might wonder why I'd need this ; it's ...
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1 vote
2 answers
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If a star passes near another star will that star feel gravitational influence immediately or with a delay? [duplicate]

If a star passes near another star will that star feel gravitational influence immediately or with a delay? Assuming that the distance is a large number and the stars are very massive?
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Would a supernova 1A appear to last longer if it were more distant and does it depend linearly on measured cosmological redshift?

Would a supernova 1A appear to last longer if seen more distant and does this depend linearly on measured cosmological redshift? I asked a question on a very popular radio station where they talked ...
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1 vote
1 answer
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Confusion with light year distance and space events

I had read that the Betelguese star may be going supernova in may of 2022. Now it is about 500 Light years away, so if we see a supernova explosion in may, then does that mean it occurred about 500 ...
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22 votes
5 answers
2k views

When we say 'Andromeda galaxy is 2 500 000 light years away from us' do we mean 'now' or in a far past?

When we say 'Andromeda galaxy is 2 500 000 light years away from us do we mean 'now' or in a far past and can this past be calculated easily?
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1 vote
1 answer
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Why the parsec (pc) is still a good cosmological definition in the curved spacetime in a large scale of universe?

The parsec (pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years or 206,000 astronomical units (au), i....
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5 votes
3 answers
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What is the "true" distance an object travels based on relative speeds?

There are two objects (x and y) with x travelling at 10km/h and y travelling at 11km/h, both with respect to the earth. After 1h, from the perspective of the earth, y travels 11km, but from the ...
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1 vote
1 answer
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Distance given two velocities

I have a home trainer that is connected to an application that I am writing which needs to calculate a distance traveled given the speeds that the trainer is sending. As such, every second, the ...
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0 answers
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Relation between proper distance and comoving distance

I have a doubt regarding the comoving distance and the proper distance. be $t_e$ the time of emission of a photon at comoving coordinates (0,0,0) and $t_0$ the time the photon is received at ...
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Ryden Eqn 5.49, Proper distance with changing scale factor

In Chapter 5 on Barbara Ryden Intro to a Cosmology 2nd ed, she presents this equation for calculating the proper distance at current time ($t_0$) to a distant galaxy whose light emitted at time $t_e$ ...
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On the decibels of a Heartbeat

I am trying to gauge the strength of the super-senses of a character from a novel, and I am seeing exactly the decibel range he can hear. The situation is being able to hear heartbeats, but I am ...
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1 answer
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Why does the estimation of the distance of supernovae depends on the cosmological model?

I was reading a paper from arxiv (https://arxiv.org/abs/1312.5798) when I stumbled upon this passage at pag 4 "However, even at low redshifts, there are limitations to how well the Type Ia ...
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1 answer
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Light cone shape

Looking at figures such as on the following page: Is the cosmic horizon related to the Big Bang event? I am a bit confused about the shape of the light cone. In the top diagram (proper distance) it ...
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1 vote
2 answers
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How to distinct between far loud voice and near soft voice?

How to distinct between far loud voice and near soft voice? Imagine a voice assistant robot trying to know if a person is commanding with her louder voice from a long distance or with her softer voice ...
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Breaking distance including downforce, air etc

I would like to calculate breaking distance for car from 200km/h to $100$ km/h with acceleration $-44$ m/s. I found this: $$ V_{\rm init} = 200~{\rm km/h} = 55~{\rm m/s}~,\\ V_{\rm final} = 100~{\rm ...
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1 vote
2 answers
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Why is position proportional to time squared?

Now I know some of the obvious answers to this, such as if you integrate the acceleration twice, you’ll get time squared, but what I’m really looking for is more of an intuitive answer. One of the ...
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2 answers
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Myopia far point virtual image

My textbook says that a diverging lens works by rendering the object a virtual image at the myopic eye’s far point. However, wouldn’t the eye then perceive an object farther than its far point at the ...
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1 vote
3 answers
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How does the universe preserve distance? [duplicate]

Assume I have some physical system, no matter of it's nature. Suppose also that this system can be descripted as some scalar field. So my physical object is just a function q = f(x, y, z). Imagine ...
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3 votes
1 answer
238 views

Is the size of far away galaxies smaller or larger than expected?

When items are further away, they look smaller. If we know the size of something nearby, then we can calculate the size of something a known distance far away. So if there is a galaxy whose size (...
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1 answer
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How do we measure the size (not mass but dimensions) of far away galaxies?

I understand how distances to galaxies are measured. I think I even understand how their mass might be measured (by their orbital trajectories?). But how can we know How big far away stars are? Like ...
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4 votes
2 answers
351 views

Difference between distance and norm

In special relativity, different observers measure lengths of objects differently, depending on their respective velocities. However, all observers agree on the invariant inner product of two vectors (...
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0 votes
1 answer
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Forces distance dependent find derivatives of position time dependent

Suppose we have a force which is dependent on distance from some point. It is easy to find the acceleration based on the distance from that point, but in a previous question, I asked they told me that ...
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2 votes
1 answer
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Distance of the Moon Cycles

Recently, I started to search more about the orbit of the moon, and noticed there are certain periodic patterns or cycles for which I did not find any satisfactory explanation. The first cycle can be ...
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Suppose you are told that the linear size of everything in the universe has been doubled overnight. Can you test this statement? [duplicate]

Suppose you are told that the linear size of everything in the universe has been doubled overnight. Can you test this statement by measuring sizes with a meter stick? Can you test it by the fact that ...
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1 vote
1 answer
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Distances in General Relativity, near massive bodies

I've been studying the basics of General Relativity, and my question is: does it make sense to say that near a black hole (or any massive body), distances increase, the way on a topographical map the ...
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3 answers
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How is position calculated when the acceleration is not constant?

To get the position of an object we can use the equation: $$x=x_0+v_0t+\frac{1}{2}at^2$$ But now I don't have a constant acceleration, both $x_0$ and $v_0$ start at $0$ and $v$ ends at $16 \text{ m/s}$...
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1 answer
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How to calculate the speeds two objects need to move at in order to reach different destinations at the same time [closed]

For example: On a graph there are two points. Each point has a different destination. The distance between Point A and its destination is 50, and the distance between Point B is 100. The points will ...
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4 votes
2 answers
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How do I determine the exact distance from Jupiter to the Sun on a specific date?

I've recently needed to determine exactly how far Jupiter was from the Sun on April 25th 2018, when a Hubble image of Jupiter was taken. I'm a beginner in physics and Google searches lead me nowhere. ...
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2 answers
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Variables in rectilinear motion

I wrote a post few days earlier on circular motion but it seems i still haven't got the hang of it yet. When is this equation actually true? $s=ut+\frac{1}{2}at^2$ Suppose velocity is given by $v=t-2$ ...
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0 votes
1 answer
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Work in different forces over the same distance [closed]

If two forces are different (Force A < Force B) but the distance over which the forces are applied is the same, then by the work formula, the object that is pushed with force B should have more ...
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2 votes
1 answer
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Can we observe an event that occurs more than 13.7 billion light years away? [duplicate]

In Kurzgesagt's latest video about the largest black holes, the narrator says that two black holes have been observed orbiting each other at a distance of 17 billion light years from Earth. So light ...
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1 answer
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How can the strong force, which is conservative, not follow the inverse square law?

In terms, which someone with a background in chemical physics & quantum chemistry might understand, what is the evidence that the strong force, across whatever its range is, follows something ...
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8 votes
3 answers
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Regarding distance laws of gravity from “A Brief History of Time” and why the Earth doesn't fall into the Sun

In “A Brief History of Time”, Hawking explains Newtonian gravity in Chapter 2, Space and Time. The further apart the bodies are, the smaller the force. The gravitational attraction of a star is ...
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