Questions tagged [distance]
The distance tag has no usage guidance.
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How exactly is conformal time, $\eta$, calculated?
As I understand it, Conformal Time is basically the comoving distance divided by the speed of light.
$$\eta=\int_0^t\frac {dt'}{a(t')}$$
I can make the connection between the scale factor and redshift:...
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1answer
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How large would the Moon have to be such that I could not see it in its entirety from earth? [on hold]
The [^circumference of the] moon can be seen in its entirety from Earth [^during a full moon] taking up a very small portion of the visible sky. The Moon is ~1/4 the diameter of the Earth. If for the ...
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2answers
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Paradox are all 4D distances zero?
The 4 dimension distance from the origin of a point is $\sqrt{x^2+y^2+z^2-t^2}$. Which means the 4 dimensional distance on the light-cone is zero.
Take a point A and a point B in the future at ...
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0answers
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Is it possible that D-T graph could be linear , but V-T graph will be log?
So , I have plotted the V-T & D-T plots for solar sail using the parameters (Using euler's method for solving the ODE based on Solar sail, estimate force & Here's my program :- https://github....
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2answers
62 views
Proper distance in cosmology
If considering two galaxies $\mathcal{A}$ and $\mathcal{B}$ being separated by $d$ ($d$ being the comoving distance) and light is emmited from $\mathcal{A}$ at time $t_1$ and that light is received to ...
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1answer
56 views
Distance Travelled by a Projectile [closed]
I was trying to find the distance travelled by a Projectile during its time of flight, $t=\dfrac{2u\sin \theta}{g}$. I used the Equation of the Path i.e. Trajectory and built up the Arc Length ...
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4answers
129 views
Understanding the difference between timelike and spacelike separations
From Woodhouse's General Relativity:
If $A$ is the origin and $B$ is a nearby event with coordinates $dt, dx, dy, dz$, then,
$$ds^2 = dt^2 - dx^2 - dy^2 - dz^2$$ is the same in all local inertial ...
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2answers
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Why work definition involves displacement?
$$W=\left\Vert\vec{F}\right\Vert \left\Vert\Delta\vec{r}\right\Vert \cos{\theta}$$ A greater magnitude force will have a greater influence than a smaller magnitude one when they have the same $\theta \...
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2answers
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Why isn't the GPS location calculated from the Schwarzschild metric?
The GPS uses the flat space light propagation formula to calculate the distance from the source (the satellite) to the receiver (observer on Earth):
$$ d=c \cdot \Delta t$$
where $c$ is the speed of ...
2
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3answers
69 views
Can length contraction help the moving observer reach a star system 'faster'? [duplicate]
Would an observer moving with close to the speed of light ($\sim 99\%$) towards a star system that's $20$ light years away perceive the distance as being less than $20$ light-years? If yes, how much ...
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1answer
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Calculating the distance between two masses with respect to gravitational force [duplicate]
Call them $m_1,m_2$. They are compressed to their center of masses, if you wish. If the initial distance at $t=0$ is $d$, is there a formula or an efficient way to calculate the distance between them ...
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4answers
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Are any of Euclid's 5 postulates false in Minkowski spacetime?
I often hear that Minkowski spacetime is non-euclidean. Euclidean geometry is characterized by Euclid's five postulates being true. Which of those postulates are untrue in Minkowski spacetime (if any),...
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4answers
101 views
Why is Work equal to Force * distance?
I totally get the mathematical part, but I cannot imagine how this works. I apply a force to a ball. Why does the distance over which it moves matter to me? Sure, if I calculate the kinetic Energy of ...
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1answer
68 views
Shortening of distances in Relativity Theory
I am studying relativity theory and I have understood why distances become shorter from the perspective of someone who is travelling close to the speed of light. However, later on I read that the ...
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1answer
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Compare 2d metric to metric on sphere-puzzling result
I calculated the infinitisimal distance squared $(\mathrm{d}s)^2$ in 3d polar coordinates and 3d cartesian coordinates in an example to show that they were identical.
I chose $P(r,\theta,\phi)$ as ...
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2answers
50 views
Are distance and displacement always frame independent?
I'm aware that distance and displacement, both are independent of reference frames, when the two frames are stationary wrt each other. Because the actual distance (or the shortest distance) between ...
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2answers
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'Ambiguity' of dual vectors $\{dx^i\}$ in cotangent space in general relativity
The metric tensor is defined as:
$$g = g_{ij}dx^i \otimes dx^j,$$
where I used the summation convention. We often omit the tensor product sign $\otimes$ and just write this as:
$$g = g_{ij}dx^idx^...
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3answers
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Why is the work done by a rocket engine greater at higher speeds? [duplicate]
From this comment by orlp:
If I strap a rocket booster to a rocket in space and fire it for one second, then the work provided is much higher when the rocket is flying fast compared to when the ...
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2answers
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Is the astronomical magnitude identical to the distance? [closed]
Why do astrophysicists use Magnitude rather than the actual distance to calculate intergalactic parameters? The magnitude is the relative brightness and has no units, the typical distance requires the ...
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9answers
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Why does work depend on distance?
So the formula for work is$$
\left[\text{work}\right] ~=~ \left[\text{force}\right] \, \times \, \left[\text{distance}\right]
\,.
$$
I'm trying to get an understanding of how this represents energy.
...
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0answers
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Why are all the other sub-displacements included into to the total displacement? [closed]
Problem:
During a jaunt on your sailboat, you sail $5\,\mathrm{km}$ east, then $5\,\mathrm{km}$ southeast, and then an additional distance in an unknown direction. Your final position is $20\,\...
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2answers
160 views
Given Max Speed, Max Acceleration and Jerk - How do I calculate time?
I'm developing some python code that controls an end effector moving in a two-dimensional plane (XY). It moves through a list of points sequentially and I'd like to estimate the time it will take as ...
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3answers
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Travelled displacement - how do we take care of the possibility that it might be negative?
so this is a very basic question but I can't really find a full answer.
So let's assume we have a point of mass $m$ travelling along the x-axis with a acceleration a. The travelled displacement is:
$...
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0answers
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Does the trace distance specify a unique state
In quantum information, we frequently use the trace distance (see definition) to look at how similar two states are.
If I had a known complete set of states $\{\rho_i\}$ and some unknown state $\...
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2answers
47 views
Can we determine the distance from a radio station (antenna) and a receiver using radio wave ?
say we have the a receiver and radio antenna can we calculate the distance between the receiver and the antenna by a receiver if we know the frequency ?
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1answer
53 views
How loud would a sound have to be for it to travel the distance of Pittsburgh, Pennsylvania to New York, NY? [closed]
I'm just wondering if it's possible, more than anything. But if it is, how many decibels would the sound have to be to travel that far of a distance?
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2answers
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How far can a shout travel?
I was wondering, if a person climbs a tower and shouts at the top of his lungs how much distance would the sound travel ? Would it reach someone 1km far? Assuming that there are no tall buildings in ...
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1answer
79 views
How much energy needed to cross the galaxy in time $t$?
Sorry if this is a dumb question.
A friend of mine just asserted that it's possible to get anywhere in the universe in less than 30 seconds of your time due to time dilation. I do imagine that'll ...
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0answers
69 views
How far are we from the “edge” of the universe? [duplicate]
According the the Big Bang theory, the universe started as a 0-dimensional point of infinite density. Shortly thereafter, it underwent inflation and grew to some measurable size, and continues growing ...
1
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1answer
50 views
How accurately can the distance of a star be measured?
With the launch of the GAIA mission some years ago, a new precedent was set in mankind's ability to map our universe. However, how accurate are the distances created by this? From ESA's website, I ...
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1answer
259 views
Calculate distance an accelerometer moved
I am reading accelerometer data and want to determine the distance that the accelerometer is moved. ( My question is similar to the one placed here, Calculate speed from accelerometer . I just feel as ...
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0answers
43 views
Is there a difference between horizon and comoving distances?
I wonder if there a difference between horizon and comoving distances in cosmology ?
I mean both correspond to a null geodesic $(ds^2=0)$ right ?
0
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1answer
77 views
The distance of an object undergoing constant acceleration
Is the distance an object moving increases with time if it is accelerated with a constant rate?
I mean, doesn't it depend on the direction the object is traveling? if I throw an object upward, ...
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1answer
40 views
Galactic Distances
I'm trying to show:
1 arcsec on the sky is approximately 5d parsecs at a galaxy, d parsecs away
Could someone show me a proof of this statement, because it is bamboozling me!
2
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1answer
821 views
The difference between comoving and proper distances in defining the observable universe
"The radius of the observable universe is estimated to be about 46.5 Gly."
If I understand correctly, it means the most distant object that we can see right now is 46.5 Gly away (at present), but it ...
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0answers
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Calculation of distance modulus in cosmology [duplicate]
I have read that absolute magnitude is a measure of the luminosity of an astronomical object. Is there any mathematical relation between luminosity (L)and absolute magnitude (M)? And how apparent ...
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8answers
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Does the mass of a bicycle directly affect stopping distance?
In this answer on the cycling SE, the claim is made that adding more mass to a bicycle increases the stopping distance. I was under the impression that mass should not affect the stopping distance so ...
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1answer
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Inverse square rule for strong forces
Most of the forces induced by a point particle follows the $1/r^2$ rule. Then why does the strong force not obey it?
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1answer
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Why are distances in cosmology larger with $\Lambda$?
I'm starting to study cosmology on these beautiful notes: http://www.damtp.cam.ac.uk/user/db275/Cosmology/Lectures.pdf .
At page 16, when talking about distances in cosmology, the author says that ...
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2answers
75 views
What is the simplest way to find the distance of stars?
Once, I was staring at the sky and wanted to know the distance to stars I could see. I searched the Internet but didn't find any easy to use tools. The distance to stars can be measured using ...
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1answer
47 views
How calculate maximum distance for an Infrared floodlight
I got an IR-light 850nm which should radiate about 180m wide, The beam angle is 10°. I measured the following values with a laser power meter.
...
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1answer
49 views
How can distance and temperature be commensurable?
I am sorry to intrude. The discipline I know something about is metaphysics rather than physics itself. And on Stack Exchange I spend my time on English Language and Usage.
I am struggling ...
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2answers
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Distance and Displacement from a velocity vs. time graph
My teacher is saying that the distance covered will be equal to the area of the trapezium in the graph, but the displacement will be equal to the area of the triangle (with purple hypotenuse). I ...
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1answer
31 views
Different time for same amount of kph/mph change at different speeds
First of all excuse me if my english isn't perfect, and if the question is hard to understand, even I am a little confused about what do I even want to ask.
So I bought a new wristwatch not too long ...
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3answers
487 views
Distance traveled equals area under velocity time graph [duplicate]
I know that for the particular case where the velocity of an object along a straight line is constant, the area beneath the velocity as a function of the time passed curve equals to the distance ...
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1answer
264 views
Parallax versus Redshift when measuring astronomical distances?
From my understanding, the most common method for calculating how far away stars and galaxies are relative to us is by accounting for their redshift. I feel that this method could be inaccurate, ...
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2answers
272 views
How far can I spray water in a straight line from a pump knowing the pressure and flow rate?
I want to build a water gun (think super soaker) powered by a water pump.
If I know the flow rate and pressure of a pump, can I calculate how far a jet of water will go in a straight line, assuming ...
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1answer
67 views
What is the relationship between heights and jet distance of water?
I'm doing an experiment on "Relationships between heights and jet distances of water". I used a bottle with a hole in it and change the height of the bottle as the column of water spout out of the ...
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0answers
155 views
Distance from the center of earth to Lagrange point L1 (Earth-Moon system)
I have derived an equation for the distance from the center of earth to the L1. I have then used python to solve this equation (approximately). I have obtained a value of 326045071m (326045km).
I ...
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5answers
363 views
Two cannons are fired from a boat, boat A is closer and boat B further. Which gets hit first?
A battleship (X) simultaneously fires two cannons towards two enemy ships. One close by (A) and one far away (B). The canon leave the battleship at different angles and travel along trajectories. ...
